Active object

From Rosetta Code
Task
Active object
You are encouraged to solve this task according to the task description, using any language you may know.


In object-oriented programming an object is active when its state depends on clock. Usually an active object encapsulates a task that updates the object's state. To the outer world the object looks like a normal object with methods that can be called from outside. Implementation of such methods must have a certain synchronization mechanism with the encapsulated task in order to prevent object's state corruption.

A typical instance of an active object is an animation widget. The widget state changes with the time, while as an object it has all properties of a normal widget.

The task

Implement an active integrator object. The object has an input and output. The input can be set using the method Input. The input is a function of time. The output can be queried using the method Output. The object integrates its input over the time and the result becomes the object's output. So if the input is K(t) and the output is S, the object state S is changed to S + (K(t1) + K(t0)) * (t1 - t0) / 2, i.e. it integrates K using the trapeze method. Initially K is constant 0 and S is 0.

In order to test the object:

  1. set its input to sin (2π f t), where the frequency f=0.5Hz. The phase is irrelevant.
  2. wait 2s
  3. set the input to constant 0
  4. wait 0.5s

Verify that now the object's output is approximately 0 (the sine has the period of 2s). The accuracy of the result will depend on the OS scheduler time slicing and the accuracy of the clock.


Ada

with Ada.Calendar;                       use Ada.Calendar;
with Ada.Numerics;                       use Ada.Numerics;
with Ada.Numerics.Elementary_Functions;  use Ada.Numerics.Elementary_Functions;
with Ada.Text_IO;                        use Ada.Text_IO;
 
procedure Test_Integrator is
   type Func is access function (T : Time) return Float;

   function Zero (T : Time) return Float is
   begin
      return 0.0;
   end Zero;

   Epoch : constant Time := Clock;

   function Sine (T : Time) return Float is
   begin
      return Sin (Pi * Float (T - Epoch));
   end Sine;

   task type Integrator is
      entry Input  (Value : Func);
      entry Output (Value : out Float);
      entry Shut_Down;
   end Integrator;
 
   task body Integrator is
      K  : Func  := Zero'Access;
      S  : Float := 0.0;
      F0 : Float := 0.0;
      F1 : Float;
      T0 : Time  := Clock;
      T1 : Time;
   begin
      loop
         select
            accept Input (Value : Func) do
               K := Value;
            end Input;
         or accept Output (Value : out Float) do
               Value := S;
            end Output;
         or accept Shut_Down;
            exit;
         else
            T1 := Clock;
            F1 := K (T1);
            S  := S + 0.5 * (F1 + F0) * Float (T1 - T0);
            T0 := T1;
            F0 := F1;
         end select;
      end loop;
   end Integrator;
 
   I : Integrator;
   S : Float;
begin
   I.Input (Sine'Access);
   delay 2.0;
   I.Input (Zero'Access);
   delay 0.5;
   I.Output (S);
   Put_Line ("Integrated" & Float'Image (S) & "s");
   I.Shut_Down;
end Test_Integrator;

Sample output:

Integrated-5.34100E-05s

ATS

No memory management is needed. Everything is done in registers or on the stack, including the closure that is used to connect signal source and integrator.

The core code is templates for any floating point type, but, in the end, one must choose a type. Our choice is C float type.

(*------------------------------------------------------------------*)
(* I will not bother with threads. All we need is the ability to get
   the time from the operating system. This is available as
   clock(3). *)

#define ATS_PACKNAME "rosettacode.activeobject"
#define ATS_EXTERN_PREFIX "rosettacode_activeobject_"

#include "share/atspre_staload.hats"

(*------------------------------------------------------------------*)
(* Some math functionality, for all the standard floating point
   types. The ats2-xprelude package includes this, and more, but one
   may wish to avoid the dependency. And there is support for math
   functions in libats/libc, but not with typekinds. *)

%{^
#include <math.h>
// sinpi(3) would be better than sin(3), but I do not yet have
// sinpi(3).
#define rosettacode_activeobject_pi \
  3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706798214L
#define rosettacode_activeobject_sinpi_float(x) \
  (sinf (((atstype_float) rosettacode_activeobject_pi) * (x)))
#define rosettacode_activeobject_sinpi_double \
  (sin (((atstype_double) rosettacode_activeobject_pi) * (x)))
#define rosettacode_activeobject_sinpi_ldouble \
  (sinl (((atstype_ldouble) rosettacode_activeobject_pi) * (x)))
%}

extern fn sinpi_float : float -<> float = "mac#%"
extern fn sinpi_double : double -<> double = "mac#%"
extern fn sinpi_ldouble : ldouble -<> ldouble = "mac#%"
extern fn {tk : tkind} g0float_sinpi : g0float tk -<> g0float tk
implement g0float_sinpi<fltknd> x = sinpi_float x
implement g0float_sinpi<dblknd> x = sinpi_double x
implement g0float_sinpi<ldblknd> x = sinpi_ldouble x

overload sinpi with g0float_sinpi

(*------------------------------------------------------------------*)
(* Some clock(3) functionality for the three standard floating point
   types. *)

%{^
#include <time.h>

typedef clock_t rosettacode_activeobject_clock_t;

ATSinline() rosettacode_activeobject_clock_t
rosettacode_activeobject_clock () // C23 drops the need for "void".
{
  return clock ();
}

ATSinline() rosettacode_activeobject_clock_t
rosettacode_activeobject_clock_difference
          (rosettacode_activeobject_clock_t t,
           rosettacode_activeobject_clock_t t0)
{
  return (t - t0);
}

ATSinline() atstype_float
rosettacode_activeobject_clock_scaled2float
          (rosettacode_activeobject_clock_t t)
{
  return ((atstype_float) t) / CLOCKS_PER_SEC;
}

ATSinline() atstype_double
rosettacode_activeobject_clock_scaled2double
          (rosettacode_activeobject_clock_t t)
{
  return ((atstype_double) t) / CLOCKS_PER_SEC;
}

ATSinline() atstype_ldouble
rosettacode_activeobject_clock_scaled2ldouble
          (rosettacode_activeobject_clock_t t)
{
  return ((atstype_ldouble) t) / CLOCKS_PER_SEC;
}
%}

typedef clock_t = $extype"clock_t"
extern fn clock : () -<> clock_t = "mac#%"
extern fn clock_difference : (clock_t, clock_t) -<> clock_t = "mac#%"
extern fn clock_scaled2float : clock_t -<> float = "mac#%"
extern fn clock_scaled2double : clock_t -<> double = "mac#%"
extern fn clock_scaled2ldouble : clock_t -<> ldouble = "mac#%"

extern fn {tk : tkind} clock_scaled2g0float : clock_t -<> g0float tk

implement clock_scaled2g0float<fltknd> t = clock_scaled2float t
implement clock_scaled2g0float<dblknd> t = clock_scaled2double t
implement clock_scaled2g0float<ldblknd> t = clock_scaled2ldouble t

overload - with clock_difference
overload clock2f with clock_scaled2g0float

(*------------------------------------------------------------------*)

%{^
#if defined __GNUC__ && (defined __i386__ || defined __x86_64__)
// A small, machine-dependent pause, for improved performance of spin
// loops.
#define rosettacode_activeobject_pause() __builtin_ia32_pause ()
#else
// Failure to insert a small, machine-dependent pause may overwork
// your hardware, but the task can be done anyway.
#define rosettacode_activeobject_pause() do{}while(0)
#endif
%}

extern fn pause : () -<> void = "mac#%"

(*------------------------------------------------------------------*)

(* Types such as this can have their internals hidden, but here I will
   not bother with such details. *)
vtypedef sinusoidal_generator (tk : tkind) =
  @{
    phase   = g0float tk,
    afreq   = g0float tk,    (* angular frequency IN UNITS OF 2*pi. *)
    clock0  = clock_t,
    stopped = bool
  }

fn {tk : tkind}
sinusoidal_generator_Initize
          (gen   : &sinusoidal_generator tk?
                    >> sinusoidal_generator tk,
           phase : g0float tk,
           afreq : g0float tk) : void =
  gen := @{phase = phase,
           afreq = afreq,
           clock0 = clock (),
           stopped = true}

fn {tk : tkind}
sinusoidal_generator_Start
          (gen : &sinusoidal_generator tk) : void =
  gen.stopped := false

(* IMO changing the integrator's input is bad OO design: akin to
   unplugging one generator and plugging in another. What we REALLY
   want is to have the generator produce a different signal. So
   gen.Stop() will connect the output to a constant
   zero. (Alternatively, the channel between the signal source and the
   integrator could effect the shutoff.) *)
fn {tk : tkind}
sinusoidal_generator_Stop
          (gen : &sinusoidal_generator tk) : void =
  gen.stopped := true

fn {tk : tkind}
sinusoidal_generator_Sample
          (gen : !sinusoidal_generator tk) : g0float tk =
  let
    val @{phase = phase,
          afreq = afreq,
          clock0 = clock0,
          stopped = stopped} = gen
  in
    if stopped then
      g0i2f 0
    else
      let
        val t = (clock2f (clock () - clock0)) : g0float tk
      in
        sinpi ((afreq * t) + phase)
      end
  end

overload .Initize with sinusoidal_generator_Initize
overload .Start with sinusoidal_generator_Start
overload .Stop with sinusoidal_generator_Stop
overload .Sample with sinusoidal_generator_Sample

(*------------------------------------------------------------------*)

vtypedef inputter (tk : tkind, p : addr) =
  (* This is a closure type that can reside either in the heap or on
     the stack. *)
  @((() -<clo1> g0float tk) @ p | ptr p)

vtypedef active_integrator (tk : tkind, p : addr) =
  @{
    inputter    = inputter (tk, p),
    t_last      = clock_t,
    sample_last = g0float tk,
    integral    = g0float tk
  }
vtypedef active_integrator (tk : tkind) =
  [p : addr] active_integrator (tk, p)

fn {tk : tkind}
active_integrator_Input
          {p : addr}
          (igrator  : &active_integrator tk?
                        >> active_integrator (tk, p),
           inputter : inputter (tk, p)) : void =
  let
    val now = clock ()
  in
    igrator := @{inputter = inputter,
                 t_last = now,
                 sample_last = g0i2f 0,
                 integral = g0i2f 0}
  end

fn {tk : tkind}
active_integrator_Output
          {p : addr}
          (igrator : !active_integrator (tk, p)) : g0float tk =
  igrator.integral

fn {tk : tkind}
active_integrator_Integrate
          {p : addr}
          (igrator : &active_integrator (tk, p)) : void =
  let
    val @{inputter = @(pf | p),
          t_last = t_last,
          sample_last = sample_last,
          integral = integral} = igrator
    macdef inputter_closure = !p

    val t_now = clock ()
    val sample_now = inputter_closure ()

    val integral = integral + ((sample_last + sample_now)
                               * clock2f (t_last - t_now)
                               * g0f2f 0.5)
    val sample_last = sample_now
    val t_last = t_now

    val () = igrator := @{inputter = @(pf | p),
                          t_last = t_last,
                          sample_last = sample_last,
                          integral = integral}
  in
  end

overload .Input with active_integrator_Input
overload .Output with active_integrator_Output
overload .Integrate with active_integrator_Integrate

(*------------------------------------------------------------------*)

implement
main () =
  let
    (* We put on the stack all objects that are not in registers. Thus
       we avoid the need for malloc/free. *)

    vtypedef gen_vt = sinusoidal_generator float_kind
    vtypedef igrator_vt = active_integrator float_kind

    var gen : gen_vt
    var igrator : igrator_vt

    val phase = 0.0f
    and afreq = 1.0f            (* Frequency of 0.5 Hz. *)
    val () = gen.Initize (phase, afreq)
    val () = gen.Start ()

    (* Create a thunk on the stack. This thunk acts as a channel
       between the sinusoidal generator and the active integrator. We
       could probably work this step into the OO style of most of the
       code, but doing that is left as an exercise. The mechanics of
       creating a closure on the stack are already enough for a person
       to absorb. (Of course, rather than use a closure, we could have
       set up a type hierarchy. However, IMO a type hierarchy is
       needlessly clumsy. Joining the objects with a closure lets any
       thunk of the correct type serve as input.) *)
    val p_gen = addr@ gen
    var gen_clo_on_stack =
      lam@ () : float =<clo1>
        let
          (* A little unsafeness is needed here. AFAIK there is no way
             to SAFELY enclose the stack variable "gen" in the
             closure. A negative effect is that (at least without some
             elaborate scheme) it becomes POSSIBLE to use this
             closure, even after "gen" has been destroyed. But we will
             be careful not to do that. *)
          extern praxi p2view :
            {p : addr} ptr p -<prf>
              (gen_vt @ p, gen_vt @ p -<lin,prf> void)
          prval @(pf, fpf) = p2view p_gen
          macdef gen = !p_gen
          val sample = gen.Sample ()
          prval () = fpf pf
        in
          sample
        end
    val sinusoidal_inputter =
      @(view@ gen_clo_on_stack | addr@ gen_clo_on_stack)

    val () = igrator.Input (sinusoidal_inputter)

    fn {}
    integrate_for_seconds
              (igrator : &igrator_vt,
               seconds : float) : void =
      let
        val t0 = clock2f (clock ())
        fun
        loop (igrator : &igrator_vt) : void =
          if clock2f (clock ()) - t0 < seconds then
            begin
              igrator.Integrate ();
              pause ();
              loop igrator
            end
      in
        loop igrator
      end

    (* Start the sinusoid and then integrate for 2.0 seconds. *)
    val () = gen.Start ()
    val () = integrate_for_seconds (igrator, 2.0f)

    (* Stop the sinusoid and then integrate for 0.5 seconds. *)
    val () = gen.Stop ()
    val () = integrate_for_seconds (igrator, 0.5f)

    val () = println! ("integrator output = ", igrator.Output ());

    (* The following "prval" lines are necessary for type-safety, and
       produce no executable code. *)
    prval @{inputter = @(pf | _),
            t_last = _,
            sample_last = _,
            integral = _} = igrator
    prval () = view@ gen_clo_on_stack := pf
  in
    0
  end

(*------------------------------------------------------------------*)
Output:

One will get different results on different runs.

$ patscc -std=gnu2x -Ofast active_object_task.dats -lm && ./a.out
integrator output = -0.000002

BASIC

BBC BASIC

      INSTALL @lib$+"CLASSLIB"
      INSTALL @lib$+"TIMERLIB"
      INSTALL @lib$+"NOWAIT"
      
      REM Integrator class:
      DIM integ{f$, t#, v#, tid%, @init, @@exit, input, output, tick}
      PROC_class(integ{})
      
      REM Methods:
      DEF integ.@init integ.f$ = "0" : integ.tid% = FN_ontimer(10, PROC(integ.tick), 1) : ENDPROC
      DEF integ.@@exit PROC_killtimer(integ.tid%) : ENDPROC
      DEF integ.input (f$) integ.f$ = f$ : ENDPROC
      DEF integ.output = integ.v#
      DEF integ.tick integ.t# += 0.01 : integ.v# += EVAL(integ.f$) : ENDPROC
      
      REM Test:
      PROC_new(myinteg{}, integ{})
      PROC(myinteg.input) ("SIN(2*PI*0.5*myinteg.t#)")
      PROCwait(200)
      PROC(myinteg.input) ("0")
      PROCwait(50)
      PRINT "Final value = " FN(myinteg.output)
      PROC_discard(myinteg{})

Output:

Final value = -1.43349462E-6

C

Uses POSIX threads.

Library: pthread
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <math.h>
#include <sys/time.h>
#include <pthread.h>

/* no need to lock the object: at worst the readout would be 1 tick off,
   which is no worse than integrator's inate inaccuracy */
typedef struct {
	double (*func)(double);
	struct timeval start;
	double v, last_v, last_t;
	pthread_t id;
} integ_t, *integ;

void update(integ x)
{
	struct timeval tv;
	double t, v, (*f)(double);

	f = x->func;
	gettimeofday(&tv, 0);
	t = ((tv.tv_sec - x->start.tv_sec) * 1000000
		+ tv.tv_usec - x->start.tv_usec) * 1e-6;
	v = f ? f(t) : 0;
	x->v += (x->last_v + v) * (t - x->last_t) / 2;
	x->last_t = t;
}

void* tick(void *a)
{
	integ x = a;
	while (1) {
		usleep(100000); /* update every .1 sec */
		update(x);
	}
}

void set_input(integ x, double (*func)(double))
{
	update(x);
	x->func = func;
	x->last_t = 0;
	x->last_v = func ? func(0) : 0;
}

integ new_integ(double (*func)(double))
{
	integ x = malloc(sizeof(integ_t));
	x->v = x->last_v = 0;
	x->func = 0;
	gettimeofday(&x->start, 0);
	set_input(x, func);
	pthread_create(&x->id, 0, tick, x);
	return x;
}

double sine(double t) { return sin(4 * atan2(1, 1) * t); }

int main()
{
	integ x = new_integ(sine);
	sleep(2);
	set_input(x, 0);
	usleep(500000);
	printf("%g\n", x->v);

	return 0;
}

output

-9.99348e-05

C#

Works with: C# 6
using System;
using System.Threading.Tasks;

using static System.Diagnostics.Stopwatch;
using static System.Math;
using static System.Threading.Thread;

class ActiveObject
{
    static double timeScale = 1.0 / Frequency;

    Func<double, double> func;
    Task updateTask;
    double integral;
    double value;
    long timestamp0, timestamp;

    public ActiveObject(Func<double, double> input)
    {
        timestamp0 = timestamp = GetTimestamp();
        func = input;
        value = func(0);
        updateTask = Integrate();
    }

    public void ChangeInput(Func<double, double> input)
    {
        lock (updateTask)
        {
            func = input;
        }
    }

    public double Value
    {
        get
        {
            lock (updateTask)
            {
                return integral;
            }
        }
    }

    async Task Integrate()
    {
        while (true)
        {
            await Task.Yield();
            var newTime = GetTimestamp();
            double newValue;

            lock (updateTask)
            {
                newValue = func((newTime - timestamp0) * timeScale);
                integral += (newValue + value) * (newTime - timestamp) * timeScale / 2;
            }

            timestamp = newTime;
            value = newValue;
        }
    }
}

class Program
{
    static Func<double, double> Sine(double frequency) =>
        t => Sin(2 * PI * frequency * t);

    static void Main(string[] args)
    {
        var ao = new ActiveObject(Sine(0.5));
        Sleep(TimeSpan.FromSeconds(2));
        ao.ChangeInput(t => 0);
        Sleep(TimeSpan.FromSeconds(0.5));
        Console.WriteLine(ao.Value);
    }
}

Output:

8.62230019255E-5

C++

Works with: C++14
#include <atomic>
#include <chrono>
#include <cmath>
#include <iostream>
#include <mutex>
#include <thread>

using namespace std::chrono_literals;

class Integrator
{
  public:
    using clock_type = std::chrono::high_resolution_clock;
    using dur_t      = std::chrono::duration<double>;
    using func_t     = double(*)(double);

    explicit Integrator(func_t f = nullptr);
    ~Integrator();
    void input(func_t new_input);
    double output() { return integrate(); }

  private:
    std::atomic_flag continue_;
    std::mutex       mutex;
    std::thread      worker;

    func_t                       func;
    double                       state = 0;
    //Improves precision by reducing sin result error on large values
    clock_type::time_point const beginning = clock_type::now();
    clock_type::time_point       t_prev = beginning;

    void do_work();
    double integrate();
};

Integrator::Integrator(func_t f) : func(f)
{
    continue_.test_and_set();
    worker = std::thread(&Integrator::do_work, this);
}

Integrator::~Integrator()
{
    continue_.clear();
    worker.join();
}

void Integrator::input(func_t new_input)
{
    integrate();
    std::lock_guard<std::mutex> lock(mutex);
    func = new_input;
}

void Integrator::do_work()
{
    while (continue_.test_and_set()) {
        integrate();
        std::this_thread::sleep_for(1ms);
    }
}

double Integrator::integrate()
{
    std::lock_guard<std::mutex> lock(mutex);
    auto now = clock_type::now();
    dur_t start = t_prev - beginning;
    dur_t fin   =    now - beginning;
    if (func)
        state += (func(start.count()) + func(fin.count())) * (fin - start).count() / 2;
    t_prev = now;
    return state;
}

double sine(double time)
{
    constexpr double PI = 3.1415926535897932;
    return std::sin(2 * PI * 0.5 * time);
}

int main()
{
    Integrator foo(sine);
    std::this_thread::sleep_for(2s);
    foo.input(nullptr);
    std::this_thread::sleep_for(500ms);
    std::cout << foo.output();
}

output

1.23136e-011

Clojure

(ns active-object
  (:import (java.util Timer TimerTask)))

(defn input [integrator k]
  (send integrator assoc :k k))

(defn output [integrator]
  (:s @integrator))

(defn tick [integrator t1]
  (send integrator
        (fn [{:keys [k s t0] :as m}]
          (assoc m :s (+ s (/ (* (+ (k t1) (k t0)) (- t1 t0)) 2.0)) :t0 t1))))

(defn start-timer [integrator interval]
  (let [timer (Timer. true)
        start (System/currentTimeMillis)]
    (.scheduleAtFixedRate timer
                          (proxy [TimerTask] []
                            (run [] (tick integrator (double (/ (- (System/currentTimeMillis) start) 1000)))))
                          (long 0)
                          (long interval))
    #(.cancel timer)))

(defn test-integrator []
  (let [integrator (agent {:k (constantly 0.0) :s 0.0 :t0 0.0})
        stop-timer (start-timer integrator 10)]
    (input integrator #(Math/sin (* 2.0 Math/PI 0.5 %)))
    (Thread/sleep 2000)
    (input integrator (constantly 0.0))
    (Thread/sleep 500)
    (println (output integrator))
    (stop-timer)))

user> (test-integrator)
1.414065859052494E-5

Common Lisp

(defclass integrator ()
  ((input :initarg :input :writer input :reader %input)
   (lock :initform (bt:make-lock) :reader lock)
   (start-time :initform (get-internal-real-time) :reader start-time)
   (interval :initarg :interval :reader interval)
   (thread :reader thread :writer %set-thread)
   (area :reader area :initform 0 :accessor %area)))

(defmethod shared-initialize
    ((integrator integrator) slot-names &key (interval nil interval-s-p) &allow-other-keys)
  (declare (ignore interval))
  (cond
    ;; Restart the thread if any unsynchronized slots are
    ;; being initialized
    ((or
      (eql slot-names t)
      (member 'thread slot-names)
      (member 'interval slot-names)
      (member 'start-time slot-names)
      (member 'lock slot-names)
      interval-s-p)
     ;; If the instance already has a thread, stop it and wait for it
     ;; to stop before initializing any slots
     (when (slot-boundp integrator 'thread)
       (input nil integrator)
       (bt:join-thread (thread integrator)))
     (call-next-method)
     (let* ((now (get-internal-real-time))
            (current-value (funcall (%input integrator) (- (start-time integrator) now))))
       (%set-thread
        (bt:make-thread
         (lambda ()
           (loop
             ;; Sleep for the amount required to reach the next interval;
             ;; mitigates drift from theoretical interval times
             (sleep
              (mod
               (/ (- (start-time integrator) (get-internal-real-time))
                  internal-time-units-per-second)
               (interval integrator)))
             (let* ((input
                      (bt:with-lock-held ((lock integrator))
                        ;; If input is nil, exit the thread
                        (or (%input integrator) (return))))
                    (previous-time (shiftf now (get-internal-real-time)))
                    (previous-value
                      (shiftf
                       current-value
                       (funcall input (/ (- now (start-time integrator)) internal-time-units-per-second)))))
               (bt:with-lock-held ((lock integrator))
                 (incf (%area integrator)
                       (*
                        (/ (- now previous-time)
                           internal-time-units-per-second)
                        (/ (+ previous-value current-value)
                           2)))))))
         :name "integrator-thread")
        integrator)))
    (t
     ;; If lock is not in SLOT-NAMES, it must already be initialized,
     ;; so it can be taken while slots synchronized to it are set
     (bt:with-lock-held ((lock integrator))
       (call-next-method)))))

(defmethod input :around (new-value (integrator integrator))
  (bt:with-lock-held ((lock integrator))
    (call-next-method)))

(defmethod area :around ((integrator integrator))
  (bt:with-lock-held ((lock integrator))
    (call-next-method)))

(let ((integrator
        (make-instance 'integrator
                       :input (lambda (time) (sin (* 2 pi 0.5 time)))
                       :interval 1/1000)))
  (unwind-protect
       (progn
         (sleep 2)
         (input (constantly 0) integrator)
         (sleep 0.5)
         (format t "~F~%" (area integrator)))
    (input nil integrator)))

Crystal

Translation of: Python

Crystal currently runs all code in a single thread, so a trivial example wouldn't have any issues with thread safety. However, this behavior will likely change in the future. This example was written with that in mind, and is somewhat more complex to show better idioms and be future-proof.

require "math"
require "time"

# this enum allows us to specify what type of message the proc_chan received.
# this trivial example only has one action, but more enum members can be added
# to update the proc, or take other actions
enum Action
  Finished  # we've waited long enough, and are asking for our result
  # Update  # potential member representing an update to the integrator function
end

class Integrator
  property interval : Float64
  getter s : Float64 = 0f64

  # initialize our k function as a proc that takes a float and just returns 0
  getter k : Proc(Float64, Float64) = ->(t : Float64) { 0f64 }

  # channels used for communicating with the main fiber
  @proc_chan : Channel(Tuple(Action, Proc(Float64, Float64)|Nil))
  @result_chan : Channel(Float64)

  def initialize(@k, @proc_chan, @result_chan, @interval = 1e-4)
    # use a monotonic clock for accuracy
    start = Time.monotonic.total_seconds
    t0, k0 = 0f64, @k.call(0f64)

    loop do
      # this sleep returns control to the main fiber. if the main fiber hasn't finished sleeping,
      # control will be returned to this loop
      sleep interval.seconds
      # check the channel to see if the function has changed
      self.check_channel()
      t1 = Time.monotonic.total_seconds - start
      k1 = @k.call(t1)
      @s += (k1 + k0) * (t1 - t0) / 2.0
      t0, k0 = t1, k1
    end
  end

  # check the proc_chan for messages, update the integrator function or send the result as needed
  def check_channel
    select
    when message = @proc_chan.receive
      action, new_k = message
      case action
      when Action::Finished
        @result_chan.send @s
        @k = new_k unless new_k.nil?
      end
    else
      nil
    end
  end
end

# this channel allows us to update the integrator function,
# and inform the integrator to send the result over the result channel
proc_chan = Channel(Tuple(Action, Proc(Float64, Float64)|Nil)).new

# channel used to return the result from the integrator
result_chan = Channel(Float64).new

# run everything in a new top-level fiber to avoid shared memory issues.
# since the fiber immediately sleeps, control is returned to the main code.
# the main code then sleeps for two seconds, returning control to our state_clock fiber.
# when two seconds is up, this state_clock fiber will return control
# to the main code on the next `sleep interval.seconds`
spawn name: "state_clock" do
  ai = Integrator.new ->(t : Float64) { Math.sin(Math::PI * t) }, proc_chan, result_chan
end

sleep 2.seconds
proc_chan.send({Action::Finished, ->(t : Float64) { 0f64 }})
sleep 0.5.seconds
puts result_chan.receive

Output:

-2.5475883655389925e-10

D

Translation of: Java
import core.thread;
import std.datetime;
import std.math;
import std.stdio;

void main() {
    auto func = (double t) => sin(cast(double) PI * t);
    Integrator integrator = new Integrator(func);
    Thread.sleep(2000.msecs);

    integrator.setFunc(t => 0.0);
    Thread.sleep(500.msecs);

    integrator.stop();
    writeln(integrator.getOutput());
}

/**
 * Integrates input function K over time
 * S + (t1 - t0) * (K(t1) + K(t0)) / 2
 */
public class Integrator {
    public alias Function = double function (double);

    private SysTime start;
    private shared bool running;

    private Function func;
    private shared double t0;
    private shared double v0;
    private shared double sum = 0.0;

    public this(Function func) {
        this.start = Clock.currTime();
        setFunc(func);
        new Thread({
            integrate();
        }).start();
    }

    public void setFunc(Function func) {
        this.func = func;
        v0 = func(0.0);
        t0 = 0.0;
    }

    public double getOutput() {
        return sum;
    }

    public void stop() {
        running = false;
    }

    private void integrate() {
        running = true;
        while (running) {
            Thread.sleep(1.msecs);
            update();
        }
    }

    private void update() {
        import core.atomic;

        Duration t1 = (Clock.currTime() - start);
        double v1 = func(t1.total!"msecs");
        double rect = (t1.total!"msecs" - t0) * (v0 + v1) / 2;
        atomicOp!"+="(this.sum, rect);
        t0 = t1.total!"msecs";
        v0 = v1;
    }
}
Output:
-3.07837e-13

Delphi

Translation of: Python
program Active_object;

{$APPTYPE CONSOLE}

uses
  System.SysUtils,
  System.Classes;

type
  TIntegrator = class(TThread)
  private
    { Private declarations }
    interval, s: double;
    IsRunning: Boolean;
  protected
    procedure Execute; override;
  public
    k: Tfunc<Double, Double>;
    constructor Create(k: Tfunc<Double, Double>; inteval: double = 1e-4); overload;
    procedure Join;
  end;

{ TIntegrator }

constructor TIntegrator.Create(k: Tfunc<Double, Double>; inteval: double = 1e-4);
begin
  self.interval := Interval;
  self.K := k;
  self.S := 0.0;
  IsRunning := True;
  FreeOnTerminate := True;
  inherited Create(false);
end;

procedure TIntegrator.Execute;
var
  interval, t0, k0, t1, k1: double;
  start: Cardinal;
begin
  inherited;

  interval := self.interval;
  start := GetTickCount;
  t0 := 0;
  k0 := self.K(0);

  while IsRunning do
  begin
    t1 := (GetTickCount - start) / 1000;
    k1 := self.K(t1);
    self.S := self.S + ((k1 + k0) * (t1 - t0) / 2.0);
    t0 := t1;
    k0 := k1;
  end;
end;

procedure TIntegrator.Join;
begin
  IsRunning := false;
end;

var
  Integrator: TIntegrator;

begin
  Integrator := TIntegrator.create(
    function(t: double): double
    begin
      Result := sin(pi * t);
    end);

  sleep(2000);

  Writeln(Integrator.s);

  Integrator.k :=
    function(t: double): double
    begin
      Result := 0;
    end;

  sleep(500);
  Writeln(Integrator.s);
  Integrator.Join;
  Readln;
end.
Output:
-1.51242391413465E-0016
-1.51242391413465E-0016

E

def makeIntegrator() {
    var value := 0.0
    var input := fn { 0.0 }
    
    var input1 := input()
    var t1 := timer.now()
    
    def update() {
        def t2 := timer.now()
        def input2 :float64 := input()
        def dt := (t2 - t1) / 1000
        
        value += (input1 + input2) * dt / 2
        
        t1 := t2
        input1 := input2
    }
    
    var task() {
        update <- ()
        task <- ()
    }
    task()
    
    def integrator {
        to input(new) :void  { input := new }
        to output() :float64 { return value }
        to shutdown()        { task := fn {} }
    }
    return integrator
}

def test() {
    def result
    
    def pi := (-1.0).acos()
    def freq := pi / 1000
    
    def base := timer.now()
    def i := makeIntegrator()
    
    i.input(fn { (freq * timer.now()).sin() })
    timer.whenPast(base + 2000, fn {
        i.input(fn {0})
    })
    timer.whenPast(base + 2500, fn {
        bind result := i.output()
        i.shutdown()
    })
    return result
}

EchoLisp

We use the functions (at ..) : scheduling, (wait ...), and (every ...) ot the timer.lib. The accuracy will be function of the browser's functions setTimeout and setInterval ...

(require 'timer)
   
;; returns an 'object' : (&lamdba; message [values]) 
;; messages : input, output, sample, inspect
(define (make-active)
		(let [
		(t0 #f) (dt 0)
		(t  0) (Kt 0) ; K(t)
		(S  0) (K  0)]
		(lambda (message . args)
		(case message
			((output) (// S 2))
			((input ) (set! K (car args))  (set! t0 #f))
			((inspect) (printf " Active obj : t0 %v t %v S %v "  t0 t Kt (// S 2 )))
			((sample)  
					(when (procedure? K) 
;; recved new K : init
					(unless t0
						(set! t0  (first args)) 
						(set! t 0)
						(set! Kt (K 0)))
						
;; integrate K(t) every time 'sample message is received
					(set! dt (- (first args) t t0)) ;; compute once K(t)
					(set! S (+ S (* dt Kt)))
					(set! t (+ t dt))
					(set! Kt (K t))
					(set! S (+ S (* dt Kt)))))
					
			    (else (error "active:bad message" message))))))
Output:
(define (experiment)
	(define (K t) (sin (*  PI t )))
	(define A (make-active))
	(define (stop)  (A 'input 0))
	(define (sample t) (A 'sample (// t 1000)))
	(define (result) (writeln 'result (A 'output)))
	
	(at 2.5 'seconds 'result)
	(every 10 'sample) ;; integrate every 10 ms
	
	(A 'input K)
	(wait 2000 'stop))

(experiment)  
    3/7/2015 20:34:18 : result
    result     0.0002266920372221955    
(experiment)   
    3/7/2015 20:34:28 : result
    result     0.00026510586971023164

Erlang

I could not see what time to use between each integration so it is the argument to task().

-module( active_object ).
-export( [delete/1, input/2, new/0, output/1, task/1] ).
-compile({no_auto_import,[time/0]}).

delete( Object ) ->
      Object ! stop.

input( Object, Fun ) ->
      Object ! {input, Fun}.

new( ) ->
      K = fun zero/1,
      S = 0,
      T0 = seconds_with_decimals(),
      erlang:spawn( fun() -> loop(K, S, T0) end ).

output( Object ) ->
      Object ! {output, erlang:self()},
      receive
      {output, Object, Output} -> Output
      end.

task( Integrate_millisec ) ->
      Object = new(),
      {ok, _Ref} = timer:send_interval( Integrate_millisec, Object, integrate ),
      io:fwrite( "New ~p~n", [output(Object)] ),
      input( Object, fun sine/1 ),
      timer:sleep( 2000 ),
      io:fwrite( "Sine ~p~n", [output(Object)] ),
      input( Object, fun zero/1 ),
      timer:sleep( 500 ),
      io:fwrite( "Approx ~p~n", [output(Object)] ),
      delete( Object ).



loop( Fun, Sum, T0 ) ->
      receive
      integrate ->
                T1 = seconds_with_decimals(),
                New_sum = trapeze( Sum, Fun, T0, T1 ),
                loop( Fun, New_sum, T1 );
      stop ->
                ok;
      {input, New_fun} ->
		loop( New_fun, Sum, T0 );
      {output, Pid} ->
                Pid ! {output, erlang:self(), Sum},
                loop( Fun, Sum, T0 )
      end.

sine( T ) ->
      math:sin( 2 * math:pi() * 0.5 * T ).

seconds_with_decimals() ->
      {Megaseconds, Seconds, Microseconds} = os:timestamp(),
      (Megaseconds * 1000000) + Seconds + (Microseconds / 1000000).

trapeze( Sum, Fun, T0, T1 ) ->
      Sum + (Fun(T1) + Fun(T0)) * (T1 - T0) / 2.

zero( _ ) -> 0.

F#

open System
open System.Threading

// current time in seconds
let now() = float( DateTime.Now.Ticks / 10000L ) / 1000.0

type Integrator( intervalMs ) as x =
  let mutable k = fun _ -> 0.0  // function to integrate
  let mutable s = 0.0           // current value
  let mutable t0 = now()        // last time s was updated
  let mutable running = true    // still running?

  do x.ScheduleNextUpdate()

  member x.Input(f) = k <- f

  member x.Output() = s

  member x.Stop() = running <- false

  member private x.Update() =
    let t1 = now()
    s <- s + (k t0 + k t1) * (t1 - t0) / 2.0
    t0 <- t1
    x.ScheduleNextUpdate()

  member private x.ScheduleNextUpdate() =
    if running then
      async { do! Async.Sleep( intervalMs )
              x.Update()
            }
      |> Async.Start
    
let i = new Integrator(10)

i.Input( fun t -> Math.Sin (2.0 * Math.PI * 0.5 * t) )
Thread.Sleep(2000)

i.Input( fun _ -> 0.0 )
Thread.Sleep(500)

printfn "%f" (i.Output())
i.Stop()

Factor

Working with dynamic quotations requires the stack effect to be known in advance. The apply-stack-effect serves this purpose.

USING: accessors alarms calendar combinators kernel locals math
math.constants math.functions prettyprint system threads ;
IN: rosettacode.active
 
TUPLE: active-object alarm function state previous-time ;

: apply-stack-effect ( quot -- quot' ) 
    [ call( x -- x ) ] curry ; inline
 
: nano-to-seconds ( -- seconds ) nano-count 9 10^ / ;
 
: object-times ( active-object -- t1 t2 ) 
    [ previous-time>> ] 
    [ nano-to-seconds [ >>previous-time drop ] keep ] bi ;
:: adding-function ( t1 t2 active-object -- function )
    t2 t1 active-object function>> apply-stack-effect bi@ +
    t2 t1 - * 2 / [ + ] curry ;
: integrate ( active-object -- )
    [ object-times ]
    [ adding-function ]
    [ swap apply-stack-effect change-state drop ] tri ;
 
: <active-object> ( -- object )
    active-object new
    0 >>state
    nano-to-seconds >>previous-time
    [ drop 0 ] >>function
    dup [ integrate ] curry 1 nanoseconds every >>alarm ;
: destroy ( active-object -- ) alarm>> cancel-alarm ;
 
: input ( object quot -- object ) >>function ;
: output ( object -- val ) state>> ;
 
: active-test ( -- )
    <active-object>
    [ 2 pi 0.5 * * * sin ] input
    2 seconds sleep
    [ drop 0 ] input
    0.5 seconds sleep
    [ output . ] [ destroy ] bi ;
MAIN: active-test
   ( scratchpad ) "rosettacode.active" run
   -5.294207647335787e-05

FBSL

The Dynamic Assembler and Dynamic C JIT compilers integrated in FBSL v3.5 handle multithreading perfectly well. However, pure FBSL infrastructure has never been designed especially to support own multithreading nor can it handle long long integers natively. Yet a number of tasks with careful design and planning are quite feasible in pure FBSL too:

#APPTYPE CONSOLE

#INCLUDE <Include\Windows.inc>

DIM Entity AS NEW Integrator(): Sleep(2000) ' respawn and do the job

Entity.Relax(): Sleep(500) ' get some rest

PRINT ">>> ", Entity.Yield(): DELETE Entity ' report and die

PAUSE

' ------------- End Program Code -------------

#DEFINE SpawnMutex CreateMutex(NULL, FALSE, "mutex")
#DEFINE LockMutex WaitForSingleObject(mutex, INFINITE)
#DEFINE UnlockMutex ReleaseMutex(mutex)
#DEFINE KillMutex CloseHandle(mutex)

CLASS Integrator
	
	PRIVATE:
	
	TYPE LARGE_INTEGER
		lowPart AS INTEGER
		highPart AS INTEGER
	END TYPE
	
	DIM dfreq AS DOUBLE, dlast AS DOUBLE, dnow AS DOUBLE, llint AS LARGE_INTEGER
	DIM dret0 AS DOUBLE, dret1 AS DOUBLE, mutex AS INTEGER, sum AS DOUBLE, thread AS INTEGER
	
	' --------------------------------------------
	SUB INITIALIZE()
		mutex = SpawnMutex
		QueryPerformanceFrequency(@llint)
		dfreq = LargeInt2Double(llint)
		QueryPerformanceCounter(@llint)
		dlast = LargeInt2Double(llint) / dfreq
		thread = FBSLTHREAD(ADDRESSOF Sampler)
		FBSLTHREADRESUME(thread)
	END SUB
	SUB TERMINATE()
		' nothing special
	END SUB
	' --------------------------------------------
	
	SUB Sampler()
		DO
			LockMutex
			Sleep(5)
			QueryPerformanceCounter(@llint)
			dnow = LargeInt2Double(llint) / dfreq
			dret0 = Task(dlast): dret1 = Task(dnow)
			sum = sum + (dret1 + dret0) * (dnow - dlast) / 2
			dlast = dnow
			UnlockMutex
		LOOP
	END SUB
	
	FUNCTION LargeInt2Double(obj AS VARIANT) AS DOUBLE
		STATIC ret
		ret = obj.highPart
		IF obj.highPart < 0 THEN ret = ret + (2 ^ 32)
		ret = ret * 2 ^ 32
		ret = ret + obj.lowPart
		IF obj.lowPart < 0 THEN ret = ret + (2 ^ 32)
		RETURN ret
	END FUNCTION
	
	PUBLIC:
	
	METHOD Relax()
		LockMutex
		ADDRESSOF Task = ADDRESSOF Idle
		UnlockMutex
	END METHOD
	
	METHOD Yield() AS DOUBLE
		LockMutex
		Yield = sum
		FBSLTHREADKILL(thread)
		UnlockMutex
		KillMutex
	END METHOD
	
END CLASS

FUNCTION Idle(BYVAL t AS DOUBLE) AS DOUBLE
	RETURN 0.0
END FUNCTION

FUNCTION Task(BYVAL t AS DOUBLE) AS DOUBLE
	RETURN SIN(2 * PI * 0.5 * t)
END FUNCTION

Typical console output:

>>> -0.000769965989580346
Press any key to continue...

FreeBASIC

#define twopi 6.2831853071795864769252867665590057684
dim shared as double S = 0     'set up the state as a global variable
dim shared as double t0, t1, ta

function sine( x as double, f as double ) as double
    return sin(twopi*f*x)
end function

function zero( x as double, f as double ) as double
    return 0
end function

sub integrate( K as function(as double, as double) as double, f as double )
    'represent input as pointers to functions
    t1 = timer
    s += (K(t1,f) + K(t0,f))*(t1-t0)/2.0
    t0 = t1
end sub

t0 = timer
ta = timer

while timer-ta <= 2.5
    if timer-ta <= 2 then integrate( @sine, 0.5 ) else integrate( @zero, 0 )
wend

print S
Output:

8.926050531860172e-07

Go

Using time.Tick to sample K at a constant frequency. Three goroutines are involved, main, aif, and tk. Aif controls access to the accumulator s and the integration function K. Tk and main must talk to aif through channels to access s and K.

package main

import (
    "fmt"
    "math"
    "time"
)

// type for input function, k.
// input is duration since an arbitrary start time t0.
type tFunc func(time.Duration) float64

// active integrator object.  state variables are not here, but in
// function aif, started as a goroutine in the constructor.
type aio struct {
    iCh chan tFunc        // channel for setting input function
    oCh chan chan float64 // channel for requesting output
}

// constructor
func newAio() *aio {
    var a aio
    a.iCh = make(chan tFunc)
    a.oCh = make(chan chan float64)
    go aif(&a)
    return &a
}

// input method required by task description.  in practice, this method is
// unnecessary; you would just put that single channel send statement in
// your code wherever you wanted to set the input function.
func (a aio) input(f tFunc) {
    a.iCh <- f
}

// output method required by task description.  in practice, this method too
// would not likely be best.  instead any client interested in the value would
// likely make a return channel sCh once, and then reuse it as needed.
func (a aio) output() float64 {
    sCh := make(chan float64)
    a.oCh <- sCh
    return <-sCh
}

// integration function that returns constant 0
func zeroFunc(time.Duration) float64 { return 0 }

// goroutine serializes access to integrated function k and state variable s
func aif(a *aio) {
    var k tFunc = zeroFunc // integration function
    s := 0.                // "object state" initialized to 0
    t0 := time.Now()       // initial time
    k0 := k(0)             // initial sample value
    t1 := t0               // t1, k1 used for trapezoid formula
    k1 := k0

    tk := time.Tick(10 * time.Millisecond) // 10 ms -> 100 Hz
    for {
        select {
        case t2 := <-tk: // timer tick event
            k2 := k(t2.Sub(t0))                        // new sample value
            s += (k1 + k2) * .5 * t2.Sub(t1).Seconds() // trapezoid formula
            t1, k1 = t2, k2                            // save time and value
        case k = <-a.iCh: // input method event: function change
        case sCh := <-a.oCh: // output method event: sample object state
            sCh <- s
        }
    }
}

func main() {
    a := newAio()                           // create object
    a.input(func(t time.Duration) float64 { // 1. set input to sin function
        return math.Sin(t.Seconds() * math.Pi)
    })
    time.Sleep(2 * time.Second) // 2. sleep 2 sec
    a.input(zeroFunc)           // 3. set input to zero function
    time.Sleep(time.Second / 2) // 4. sleep .5 sec
    fmt.Println(a.output())     // output should be near zero
}

Output:

2.4517135756807704e-05

Groovy

Translation of: Java
/**
 * Integrates input function K over time
 * S + (t1 - t0) * (K(t1) + K(t0)) / 2
 */
class Integrator {
    interface Function {
        double apply(double timeSinceStartInSeconds)
    }

    private final long start
    private volatile boolean running

    private Function func
    private double t0
    private double v0
    private double sum

    Integrator(Function func) {
        this.start = System.nanoTime()
        setFunc(func)
        new Thread({ this.&integrate() }).start()
    }

    void setFunc(Function func) {
        this.func = func
        def temp = func.apply(0.0.toDouble())
        v0 = temp
        t0 = 0.0.doubleValue()
    }

    double getOutput() {
        return sum
    }

    void stop() {
        running = false
    }

    private void integrate() {
        running = true
        while (running) {
            try {
                Thread.sleep(1)
                update()
            } catch (InterruptedException ignored) {
                return
            }
        }
    }

    private void update() {
        double t1 = (System.nanoTime() - start) / 1.0e9
        double v1 = func.apply(t1)
        double rect = (t1 - t0) * (v0 + v1) / 2.0
        this.sum += rect
        t0 = t1
        v0 = v1
    }

    static void main(String[] args) {
        Integrator integrator = new Integrator({ t -> Math.sin(Math.PI * t) })
        Thread.sleep(2000)

        integrator.setFunc({ t -> 0.0.toDouble() })
        Thread.sleep(500)

        integrator.stop()
        System.out.println(integrator.getOutput())
    }
}
Output:
0.0039642136156300455

Haskell

module Integrator (
  newIntegrator, input, output, stop,
  Time, timeInterval
) where
import Control.Concurrent (forkIO, threadDelay)
import Control.Concurrent.MVar (MVar, newMVar, modifyMVar_, modifyMVar, readMVar)
import Control.Exception (evaluate)
import Data.Time (UTCTime)
import Data.Time.Clock (getCurrentTime, diffUTCTime)

-- RC task
main = do let f = 0.5 {- Hz -}
          t0 <- getCurrentTime
          i <- newIntegrator
          input i (\t -> sin(2*pi * f * timeInterval t0 t)) -- task step 1
          threadDelay 2000000 {- µs -}                      -- task step 2
          input i (const 0)                                 -- task step 3
          threadDelay 500000 {- µs -}                       -- task step 4
          result <- output i
          stop i
          print result

---- Implementation ------------------------------------------------------

-- Utilities for working with the time type
type Time = UTCTime
type Func a = Time -> a
timeInterval t0 t1 = realToFrac $ diffUTCTime t1 t0

-- Type signatures of the module's interface
newIntegrator :: Fractional a => IO (Integrator a) -- Create an integrator
input  :: Integrator a -> Func a -> IO ()          -- Set the input function
output :: Integrator a           -> IO a           -- Get the current value
stop   :: Integrator a           -> IO ()          -- Stop integration, don't waste CPU

-- Data structures
data Integrator a = Integrator (MVar (IntState a)) -- MVar is a thread-safe mutable cell
  deriving Eq
data IntState a = IntState { func  :: Func a,      -- The current function
                             run   :: Bool,        -- Whether to keep going
                             value :: a,           -- The current accumulated value
                             time  :: Time }       -- The time of the previous update

newIntegrator = do
  now <- getCurrentTime
  state <- newMVar $ IntState { func  = const 0,
                                run   = True,
                                value = 0,
                                time  = now }
  thread <- forkIO (intThread state)  -- The state variable is shared between the thread
  return (Integrator state)           --   and the client interface object.     
                   
input  (Integrator stv) f = modifyMVar_ stv (\st -> return st { func = f })
output (Integrator stv)   = fmap value $ readMVar stv
stop   (Integrator stv)   = modifyMVar_ stv (\st -> return st { run = False })
  -- modifyMVar_ takes an MVar and replaces its contents according to the provided function.
  -- a { b = c } is record-update syntax: "the record a, except with field b changed to c"

-- Integration thread
intThread :: Fractional a => MVar (IntState a) -> IO ()
intThread stv = whileM $ modifyMVar stv updateAndCheckRun
  -- modifyMVar is like modifyMVar_ but the function returns a tuple of the new value
  -- and an arbitrary extra value, which in this case ends up telling whileM whether
  -- to keep looping.
  where updateAndCheckRun st = do
          now <- getCurrentTime
          let value' = integrate (func st) (value st) (time st) now
          evaluate value'                             -- avoid undesired laziness
          return (st { value = value', time  = now }, -- updated state
                  run st)                             -- whether to continue

integrate :: Fractional a => Func a -> a -> Time -> Time -> a
integrate f value t0 t1 = value + (f t0 + f t1)/2 * dt
  where dt = timeInterval t0 t1

-- Execute 'action' until it returns false.
whileM action = do b <- action; if b then whileM action else return ()

J

Implementation:

coclass 'activeobject'
require'dates'

create=:setinput NB. constructor

T=:3 :0
  if. nc<'T0' do. T0=:tsrep 6!:0'' end.
  0.001*(tsrep 6!:0'')-T0
)

F=:G=:0:
Zero=:0

setinput=:3 :0
  zero=. getoutput''
  '`F ignore'=: y,_:`''
  G=: F f.d._1
  Zero=: zero-G T ''
  getoutput''
)

getoutput=:3 :0
  Zero+G T''
)

Task example (code):

cocurrent 'testrig'

delay=: 6!:3

object=: conew 'activeobject'
setinput__object 1&o.@o.`''
smoutput (T__object,getoutput__object) ''

delay 2

smoutput (T__object,getoutput__object) ''
setinput__object 0:`''
smoutput (T__object,getoutput__object) ''

delay 0.5

smoutput (T__object,getoutput__object) ''

Task example (output):

0.001 0
2.002 4.71237e_6
2.004 1.25663e_5
2.504 1.25663e_5

First column is time relative to start of processing, second column is object's output at that time.

Using a task thread

Variant using an independent task thread:

delay=: 6!:3

task=: {{
  obj=. '' conew 'integra'
  F__obj=: 1 o. o.
  delay 2
  F__obj=: 0:
  delay 0.5
  s=. S__obj
  destroy__obj''
  s
}}

coclass'integra'
 reqthreads=: {{ 0&T.@''^:(0>.y-1 T.'')0 }}
 time=: 6!:1
 F=: 0:
 K=: S=: SHUTDOWN=: 0
 create=: {{
  reqthreads cores=. {.8 T. ''
  integrator t. '' T=: time''
 }}
 destroy=: {{ codestroy '' [ SHUTDOWN=: 1 }}
 integrator=: {{
  while. -.SHUTDOWN do.
   t=. time''
   k=. F t
   S=: S + (k+K)*t-T
   T=: t
   K=: k
  end.
 }}

This exhibits more timing variance because of the loose coupling of scheduling between threads:

   task''
0.0194745
   task''
_4.40316e_15
   task''
0.00874017
   task''
_0.0159841

Java

/**
 * Integrates input function K over time
 * S + (t1 - t0) * (K(t1) + K(t0)) / 2
 */
public class Integrator {

    public interface Function {
        double apply(double timeSinceStartInSeconds);
    }

    private final long start;
    private volatile boolean running;

    private Function func;
    private double t0;
    private double v0;
    private double sum;

    public Integrator(Function func) {
        this.start = System.nanoTime();
        setFunc(func);
        new Thread(this::integrate).start();
    }

    public void setFunc(Function func) {
        this.func = func;
        v0 = func.apply(0.0);
        t0 = 0;
    }

    public double getOutput() {
        return sum;
    }

    public void stop() {
        running = false;
    }

    private void integrate() {
        running = true;
        while (running) {
            try {
                Thread.sleep(1);
                update();
            } catch (InterruptedException e) {
                return;
            }
        }
    }

    private void update() {
        double t1 = (System.nanoTime() - start) / 1.0e9;
        double v1 = func.apply(t1);
        double rect = (t1 - t0) * (v0 + v1) / 2;
        this.sum += rect;
        t0 = t1;
        v0 = v1;
    }

    public static void main(String[] args) throws InterruptedException {
        Integrator integrator = new Integrator(t -> Math.sin(Math.PI * t));
        Thread.sleep(2000);

        integrator.setFunc(t -> 0.0);
        Thread.sleep(500);

        integrator.stop();
        System.out.println(integrator.getOutput());
    }
}

Output:

4.783602720556498E-13

JavaScript

Translation of: E
function Integrator(sampleIntervalMS) {
    var inputF = function () { return 0.0 };
    var sum = 0.0;
  
    var t1 = new Date().getTime();
    var input1 = inputF(t1 / 1000);
  
    function update() {
        var t2 = new Date().getTime();
        var input2 = inputF(t2 / 1000);
        var dt = (t2 - t1) / 1000;
        
        sum += (input1 + input2) * dt / 2;
        
        t1 = t2;
        input1 = input2;
    }
    
    var updater = setInterval(update, sampleIntervalMS);
  
    return ({
        input: function (newF) { inputF = newF },
        output: function () { return sum },
        shutdown: function () { clearInterval(updater) },
    });
}

Test program as a HTML fragment:

<p><span id="a">Test running...</span> <code id="b">-</code></p>

<script type="text/javascript">
    var f = 0.5;

    var i = new Integrator(1);
    var displayer = setInterval(function () { document.getElementById("b").firstChild.data = i.output() }, 100)
  
    setTimeout(function () {
        i.input(function (t) { return Math.sin(2*Math.PI*f*t) }); // test step 1
        setTimeout(function () { // test step 2
            i.input(function (t) { return 0 }); // test step 3
            setTimeout(function () { // test step 3
                i.shutdown();
                clearInterval(displayer);
                document.getElementById("a").firstChild.data = "Done, should be about 0: "
            }, 500);      
        }, 2000);
    }, 1)
</script>

Julia

Works with: Julia version 0.6

Julia has inheritance of data structures and first-class types, but structures do not have methods. Instead, methods are functions with multiple dispatch based on argument type.

mutable struct Integrator
    func::Function
    runningsum::Float64
    dt::Float64
    running::Bool
    function Integrator(f::Function, dt::Float64)
        this = new()
        this.func = f
        this.runningsum = 0.0
        this.dt = dt
        this.running = false
        return this
    end
end

function run(integ::Integrator, lastval::Float64 = 0.0)
    lasttime = time()
    while integ.running
        sleep(integ.dt)
        newtime = time()
        measuredinterval = newtime - lasttime
        newval = integ.func(measuredinterval)
        integ.runningsum += (lastval + newval) * measuredinterval / 2.0
        lasttime = newtime
        lastval = newval
    end
end

start!(integ::Integrator) = (integ.running = true; @async run(integ))
stop!(integ) = (integ.running = false)
f1(t) = sin(2π * t)
f2(t) = 0.0

it = Integrator(f1, 0.00001)
start!(it)
sleep(2.0)
it.func = f2
sleep(0.5)
v2 = it.runningsum
println("After 2.5 seconds, integrator value was $v2")

Kotlin

Translation of: Java

Athough this is a faithful translation of the Java entry, on my machine the output of the latter is typically an order of magnitude smaller than this version. I have no idea why.

// version 1.2.0

import kotlin.math.*

typealias Function = (Double) -> Double

/**
 * Integrates input function K over time
 * S + (t1 - t0) * (K(t1) + K(t0)) / 2
 */
class Integrator {
    private val start: Long
    private @Volatile var running = false
    private lateinit var func: Function
    private var t0 = 0.0
    private var v0 = 0.0
    private var sum = 0.0

    constructor(func: Function) {
        start = System.nanoTime()
        setFunc(func)
        Thread(this::integrate).start()
    }

    fun setFunc(func: Function) {
        this.func = func
        v0 = func(0.0)
        t0 = 0.0
    }

    fun getOutput() = sum

    fun stop() {
        running = false
    }

    private fun integrate() {
        running = true
        while (running) {
            try {
                Thread.sleep(1)
                update()
            }
            catch(e: InterruptedException) {
                return
            }
        }
    }

    private fun update() {
        val t1 = (System.nanoTime() - start) / 1.0e9
        val v1 = func(t1)
        val rect = (t1 - t0) * (v0 + v1) / 2.0
        sum  += rect
        t0 = t1
        v0 = v1
    }
}

fun main(args: Array<String>) {
    val integrator = Integrator( { sin(PI * it) } )
    Thread.sleep(2000)

    integrator.setFunc( { 0.0 } )
    Thread.sleep(500)

    integrator.stop()
    println(integrator.getOutput())
}

Sample output:

2.884266305153741E-4

Lingo

Parent script "Integrator":

property _sum
property _func
property _timeLast
property _valueLast
property _ms0
property _updateTimer

on new (me, func)
    if voidP(func) then func = "0.0"
    me._sum = 0.0
    -- update frequency: 100/sec (arbitrary)
    me._updateTimer = timeout().new("update", 10, #_update, me)
    me.input(func)
    return me
end

on stop (me)
    me._updateTimer.period = 0 -- deactivates timer
end

-- func is a term (as string) that might contain "t" and is evaluated at runtime
on input (me, func)
    me._func = func
    me._ms0 = _system.milliseconds
    me._timeLast = 0.0
    t = 0.0
    me._valueLast = value(me._func)
end

on output (me)
    return me._sum
end

on _update (me)
    now = _system.milliseconds - me._ms0
    t = now/1000.0
    val = value(me._func)
    me._sum = me._sum + (me._valueLast+val)*(t - me._timeLast)/2
    me._timeLast = t
    me._valueLast = val
end

In some movie script:

global gIntegrator

-- entry point
on startMovie   
    gIntegrator = script("Integrator").new("sin(PI * t)")
    timeout().new("timer", 2000, #step1)
end

on step1 (_, timer)       
    gIntegrator.input("0.0")
    timer.timeoutHandler = #step2
    timer.period = 500
end

on step2 (_, timer)
    gIntegrator.stop()
    put gIntegrator.output()
    timer.forget()
end
Output:
-- 0.0004

Lua

Pure/native Lua is not multithreaded, so this task should perhaps be marked "omit from|Lua" if following the implicit intent of the task. However, the explicit wording of the task does not seem to require a multithreaded solution. Perhaps this is cheating, but I thought it might interest the reader to see the integrator portion nonetheless, so it is demonstrated using a mock sampling method at various intervals (to simulate multithreaded updates).

local seconds = os.clock

local integrator = {
  new = function(self, fn)
    return setmetatable({fn=fn,t0=seconds(),v0=0,sum=0,nup=0},self)
  end,
  update = function(self)
    self.t1 = seconds()
    self.v1 = self.fn(self.t1)
    self.sum = self.sum + (self.v0 + self.v1) * (self.t1 - self.t0) / 2
    self.t0, self.v0, self.nup = self.t1, self.v1, self.nup+1
  end,
  input = function(self, fn) self.fn = fn end,
  output = function(self) return self.sum end,
}
integrator.__index = integrator

-- "fake multithreaded sleep()"
-- waits for "duration" seconds calling "f" at every "interval" seconds
local function sample(duration, interval, f)
  local now = seconds()
  local untilwhen, nextinterval = now+duration, now+interval
  f()
  repeat
    if seconds() >= nextinterval then f() nextinterval=nextinterval+interval end
  until seconds() >= untilwhen
end

local pi, sin = math.pi, math.sin
local ks = function(t) return sin(2.0*pi*0.5*t) end
local kz = function(t) return 0 end
local intervals = { 0.5, 0.25, 0.1, 0.05, 0.025, 0.01, 0.005, 0.0025, 0.001 }
for _,interval in ipairs(intervals) do
  local i = integrator:new(ks)
  sample(2.0, interval, function() i:update() end)
  i:input(kz)
  sample(0.5, interval, function() i:update() end)
  print(string.format("sampling interval: %f, %5d updates over 2.5s total = %.15f", interval, i.nup, i:output()))
end
Output:
sampling interval: 0.500000,     6 updates over 2.5s total = -0.003628054395752
sampling interval: 0.250000,    11 updates over 2.5s total = 0.003994231784540
sampling interval: 0.100000,    25 updates over 2.5s total = 0.001891527454886
sampling interval: 0.050000,    51 updates over 2.5s total = 0.023521980508657
sampling interval: 0.025000,   101 updates over 2.5s total = -0.000573259909112
sampling interval: 0.010000,   250 updates over 2.5s total = 0.003001745575344
sampling interval: 0.005000,   501 updates over 2.5s total = -0.000415541052666
sampling interval: 0.002500,   999 updates over 2.5s total = -0.001480800340644
sampling interval: 0.001000,  2493 updates over 2.5s total = 0.000362576907805

Mathematica /Wolfram Language

Block[{start = SessionTime[], K, t0 = 0, t1, kt0, S = 0}, 
 K[t_] = Sin[2 Pi f t] /. f -> 0.5; kt0 = K[t0]; 
 While[True, t1 = SessionTime[] - start; 
  S += (kt0 + (kt0 = K[t1])) (t1 - t0)/2; t0 = t1; 
  If[t1 > 2, K[t_] = 0; If[t1 > 2.5, Break[]]]]; S]
1.1309*10^-6

Curiously, this value never changes; it is always exactly the same (at 1.1309E-6). Note that closer answers could be achieved by using Mathematica's better interpolation methods, but it would require collecting the data (in a list), which would have a speed penalty large enough to negate the improved estimation.

Nim

In Nim, objects managed by the garbage collector are allocated in one heap per thread. In order to share an object, the active object, one solution consists to manage it manually and to create it in a shared heap.

Of course, it is necessary to take some precautions when accessing or updating the shared object. We use a lock for this purpose.

# Active object.
# Compile with "nim c --threads:on".

import locks
import os
import std/monotimes

type

  # Function to use for integration.
  TimeFunction = proc (t: float): float {.gcsafe.}

  # Integrator object.
  Integrator = ptr TIntegrator
  TIntegrator = object
    k: TimeFunction                 # The function to integrate.
    dt: int                         # Time interval in milliseconds.
    thread: Thread[Integrator]      # Thread which does the computation.
    s: float                        # Computed value.
    lock: Lock                      # Lock to manage concurrent accesses.
    isRunning: bool                 # True if integrator is running.

#---------------------------------------------------------------------------------------------------

proc newIntegrator(f: TimeFunction; dt: int): Integrator =
  ## Create an integrator.

  result = cast[Integrator](allocShared(sizeof(TIntegrator)))
  result.k = f
  result.dt = dt
  result.s = 0
  result.lock.initLock()
  result.isRunning = false

#---------------------------------------------------------------------------------------------------

proc process(integrator: Integrator) {.thread, gcsafe.} =
  ## Do the integration.

  integrator.isRunning = true
  let start = getMonotime().ticks
  var t0: float = 0
  var k0 = integrator.k(0)
  while true:
    sleep(integrator.dt)
    withLock integrator.lock:
      if not integrator.isRunning:
        break
      let t1 = float(getMonoTime().ticks - start) / 1e9
      let k1 = integrator.k(t1)
      integrator.s += (k1 + k0) * (t1 - t0) / 2
      t0 = t1
      k0 = k1

#---------------------------------------------------------------------------------------------------

proc start(integrator: Integrator) =
  ## Start the integrator by launching a thread to do the computation.
  integrator.thread.createThread(process, integrator)

#---------------------------------------------------------------------------------------------------

proc stop(integrator: Integrator) =
  ## Stop the integrator.

  withLock integrator.lock:
    integrator.isRunning = false
  integrator.thread.joinThread()

#---------------------------------------------------------------------------------------------------

proc setInput(integrator: Integrator; f: TimeFunction) =
  ## Set the function.
  withLock integrator.lock:
    integrator.k = f

#---------------------------------------------------------------------------------------------------

proc output(integrator: Integrator): float =
  ## Return the current output.
  withLock integrator.lock:
    result = integrator.s

#---------------------------------------------------------------------------------------------------

proc destroy(integrator: Integrator) =
  ## Destroy an integrator, freing the resources.

  if integrator.isRunning:
    integrator.stop()
  integrator.lock.deinitLock()
  integrator.deallocShared()

#---------------------------------------------------------------------------------------------------

from math import PI, sin

# Create the integrator and start it.
let integrator = newIntegrator(proc (t: float): float {.gcsafe.} = sin(PI * t), 1)
integrator.start()
echo "Integrator started."
sleep(2000)
echo "Value after 2 seconds: ", integrator.output()

# Change the function to use.
integrator.setInput(proc (t: float): float {.gcsafe.} = 0)
echo "K function changed."
sleep(500)

# Stop the integrator and display the computed value.
integrator.stop()
echo "Value after 0.5 more second: ", integrator.output()
integrator.destroy()
Output:
Integrator started.
Value after 2 seconds: 2.058071586661761e-06
K function changed.
Value after 0.5 more second: -3.007318220146679e-09

ooRexx

Not totally certain this is a correct implementation since the value coming out is not close to zero. It does show all of the basics of multithreading and object synchronization though.

integrater = .integrater~new(.routines~sine)   -- start the integrater function
call syssleep 2
integrater~input = .routines~zero              -- update the integrater function
call syssleep .5

say integrater~output
integrater~stop          -- terminate the updater thread

::class integrater
::method init
  expose stopped start v last_v last_t k
  use strict arg k
  stopped = .false
  start = .datetime~new   -- initial time stamp
  v = 0
  last_v = 0
  last_t = 0
  self~input = k
  self~start

-- spin off a new thread and start updating.  Note, this method is unguarded
-- to allow other threads to make calls
::method start unguarded
  expose stopped

  reply  -- this spins this method invocation off onto a new thread

  do while \stopped
    call sysSleep .1
    self~update    -- perform the update operation
  end

-- turn off the thread.  Since this is unguarded,
-- it can be called any time, any where
::method stop unguarded
  expose stopped
  stopped = .true

-- perform the update.  Since this is a guarded method, the object
-- start is protected.
::method update
  expose start v last_v t last_t k

  numeric digits 20   -- give a lot of precision

  current = .datetime~new
  t = (current - start)~microseconds
  new_v = k~call(t)    -- call the input function
  v += (last_v + new_v) * (t - last_t) / 2
  last_t = t
  last_v = new_v
  say new value is v

-- a write-only attribute setter (this is GUARDED)
::attribute input SET
  expose k last_t last_v
  self~update          -- update current values
  use strict arg k  -- update the call function to the provided value
  last_t = 0
  last_v = k~call(0)  -- and update to the zero value

-- the output function...returns current calculated value
::attribute output GET
  expose v
  return v

::routine zero
  return 0

::routine sine
  use arg t
  return rxcalcsin(rxcalcpi() * t)

::requires rxmath library

OxygenBasic

Built from scratch. The ringmaster orchestrates all the active-objects, keeping a list of each individual and its method call.

With a high precision timer the result is around -.0002

double MainTime

'===============
class RingMaster
'===============
'
indexbase 1
sys List[512] 'limit of 512 objects per ringmaster
sys max,acts
'
method Register(sys meth,obj) as sys
  sys i
  for i=1 to max step 2
    if list[i]=0 then exit for 'vacant slot
  next
  if i>=max then max+=2
  List[i]<=meth,obj
  return i 'token for deregistration etc
end method
'
method Deregister(sys *i)
  if i then List[i]<=0,0 : i=0
end method
'
method Clear()
  max=0
end method
'
method Act() 'called by the timer
  sys i,q
  for i=1 to max step 2
    q=List[i]
    if q then
      call q List[i+1] 'anon object
    end if
  next
  acts++
end method
'
end class


'=================
class ActiveObject
'=================
'
double     s,freq,t1,t2,v1,v2
sys        nfun,acts,RingToken
RingMaster *Master
'
method fun0() as double
end method
'
method fun1() as double 
  return sin(2*pi()*freq*MainTime)
end method
'
method func() as double
  select case nfun
    case 0 : return fun0()
    case 1 : return fun1()
  end select
  'error?
end method
'
method TimeBasedDuties()
  t1=t2
  v1=v2
  t2=MainTime
  v2=func
  s=s+(v2+v1)*(t2-t1)*0.5 'add slice to integral
  acts++
end method
'
method RegisterWith(RingMaster*r)
  @Master=@r
  if @Master then
    RingToken=Master.register @TimeBasedDuties,@this
  end if
end method
'
method Deregister()
  if @Master then
    Master.Deregister RingToken 'this is set to null
  end if
end method
'
method Output() as double
  return s
end method
'
method Input(double fr=0,fun=0)
  if fr then freq=fr
  nfun=fun
end method

method ClearIntegral()
  s=0
end method
'
end class


'SETUP TIMING SYSTEM
'===================

extern library "kernel32.dll"
declare QueryPerformanceCounter (quad*c)
declare QueryPerformanceFrequency(quad*f)
declare Sleep(sys milliseconds)
end extern
'
quad scount,tcount,freq
QueryPerformanceFrequency freq
double tscale=1/freq
double t1,t2
QueryPerformanceCounter scount

macro PrecisionTime(time)
  QueryPerformanceCounter tcount
  time=(tcount-scount)*tscale
end macro


'====
'TEST
'====

double       integral
double       tevent1,tevent2
RingMaster   Rudolpho
ActiveObject A
'
A.RegisterWith Rudolpho
A.input (fr=0.5, fun=1) 'start with the freqency function (1)
'
'SET EVENT TIMES
'===============

tEvent1=2.0 'seconds
tEvent2=2.5 'seconds
'
PrecisionTime t1 'mark initial time
MainTime=t1
'
'
'EVENT LOOP
'==========
'
do
  PrecisionTime t2
  MainTime=t2
  if t2-t1>=0.020 'seconds interval
    Rudolpho.Act 'service all active objects
    t1=t2
  end if
  '
  if tEvent1>=0 and MainTime>=tEvent1
    A.input (fun=0) 'switch to null function (0)
    tEvent1=-1      'disable this event from happening again
  end if
  if MainTime>=tEvent2
    integral=A.output()
    exit do 'end of session
  end if
  '
  sleep 5 'hand control to OS for a while
end do

print str(integral,4)

Rudolpho.clear

Oz

declare
  fun {Const X}
     fun {$ _} X end
  end

  fun {Now}
     {Int.toFloat {Property.get 'time.total'}} / 1000.0
  end

  class Integrator from Time.repeat
     attr
        k:{Const 0.0}
        s:0.0
        t1 k_t1
        t2 k_t2
      
     meth init(SampleIntervalMS)
        t1 := {Now}
        k_t1 := {@k @t1}
        {self setRepAll(action:Update
                        delay:SampleIntervalMS)}
        thread
           {self go}
        end
     end

     meth input(K)
        k := K
     end

     meth output($)
        @s
     end

     meth Update
        t2 := {Now}
        k_t2 := {@k @t2}
        s := @s + (@k_t1 + @k_t2) * (@t2 - @t1) / 2.0
        t1 := @t2
        k_t1 := @k_t2
     end
  end

  Pi = 3.14159265
  F = 0.5

  I = {New Integrator init(10)}
in
  {I input(fun {$ T}
              {Sin 2.0 * Pi * F * T}
           end)}

  {Delay 2000} %% ms

  {I input({Const 0.0})}

  {Delay 500} %% ms

  {Show {I output($)}}
  {I stop}

Perl

#!/usr/bin/perl

use strict;
use 5.10.0;

package Integrator;
use threads;
use threads::shared;

sub new {
	my $cls = shift;
	my $obj = bless {	t	=> 0,
				sum	=> 0,
				ref $cls ? %$cls : (),
				stop	=> 0,
				tid	=> 0,
				func	=> shift,
			}, ref $cls || $cls;

	share($obj->{sum});
	share($obj->{stop});

	$obj->{tid} = async {
		my $upd = 0.1; # update every 0.1 second
		while (!$obj->{stop}) {
			{
				my $f = $obj->{func};
				my $t = $obj->{t};

				$obj->{sum} += ($f->($t) + $f->($t + $upd))* $upd/ 2;
				$obj->{t} += $upd;
			}
			select(undef, undef, undef, $upd);
		}
	#	say "stopping $obj";
	};
	$obj
}

sub output { shift->{sum} }

sub delete {
	my $obj = shift;
	$obj->{stop} = 1;
	$obj->{tid}->join;
}

sub setinput {
	# This is surprisingly difficult because of the perl sharing model.
	# Func refs can't be shared, thus can't be replaced by another thread.
	# Have to create a whole new object... there must be a better way.
	my $obj = shift;
	$obj->delete;
	$obj->new(shift);
}

package main;

my $x = Integrator->new(sub { sin(atan2(1, 1) * 8 * .5 * shift) });

sleep(2);
say "sin after 2 seconds: ", $x->output;

$x = $x->setinput(sub {0});

select(undef, undef, undef, .5);
say "0 after .5 seconds: ", $x->output;

$x->delete;

Phix

classes

Library: Phix/Class
requires("0.8.2")
 
integer xlock = init_cs()
 
class integrator
--
-- Integrates input function f over time
-- v + (t1 - t0) * (f(t1) + f(t0)) / 2
--
    integer f   -- function f(atom t); (see note)
    atom interval, t0, k0 = 0, v = 0
    bool running
    public integer id
 
    procedure set_func(integer rid)
        this.f = rid
    end procedure
 
    procedure update()
        enter_cs(xlock)
        integer f = this.f  -- (nb: no "this")
        atom t1 = time(),
             k1 = f(t1)
        v += (t1 - t0) * (k1 + k0) / 2
        t0 = t1
        k0 = k1
        leave_cs(xlock)
    end procedure
 
    procedure tick()
        running = true
        while running do
            sleep(interval)
            update()
        end while
    end procedure
 
    procedure stop()
        running = false
        wait_thread(id)
    end procedure
 
    function get_output()
        return v
    end function
 
end class
 
function new_integrator(integer rid, atom interval)
    integrator i = new({rid,interval,time()})
    i.update()
    i.id = create_thread(i.tick,{i})
    return i
end function
 
function zero(atom /*t*/) return 0 end function
function sine(atom t) return sin(2*PI*0.5*t) end function
 
integrator i = new_integrator(sine,0.01);
sleep(2) 
?i.get_output()
i.set_func(zero)
sleep(0.5)
i.stop()
?i.get_output()

Note that were f a regular member function of the class, it would get a "this" parameter/argument, which we avoid by stashing it in a local integer prior to the call. Alternatively you could of course use zero/sine functions with an ignored parameter and the usual this.f() syntax [along with the usual "this." being optional inside the class definition].

Output:
0.0003532983803
4.049495114e-17

pre-classes

Note that in Phix you cannot pass a variable to another procedure and have it "change under your feet". [erm, now you can, see classes above]
The copy-on-write semantics mean it would not have any effect, in that the original would be preserved (deemed in phix to be a "very good thing") while the value passed along, a shared reference until it gets modified and a copy made, would most likely simply be discarded, unless explicitly returned and stored, which obviously cannot be done from a separate thread. Instead we pass around an index (dx) as a way of emulating the "pointer references" of other languages.

If anything phix requires more locking that other languages due to the hidden shared reference counts.
Just lock everything, it is not that hard, and you should never need much more than the stuff below.

sequence x = {}
enum TERMINATE, INTERVAL, KFUN, VALUE, T0, K0, ID, ISIZE=$
integer xlock = init_cs()

function zero(atom /*t*/) return 0 end function
function sine(atom t) return sin(2*PI*0.5*t) end function

procedure update(integer dx)
    enter_cs(xlock)
    atom t1 = time(),
         k1 = call_func(x[dx][KFUN],{t1})
    x[dx][VALUE] += (k1 + x[dx][K0]) * (t1 - x[dx][T0]) / 2
    x[dx][T0] = t1
    x[dx][K0] = k1
    leave_cs(xlock)
end procedure

procedure tick(integer dx)
    while not x[dx][TERMINATE] do
        sleep(x[dx][INTERVAL])
        update(dx)
    end while
end procedure

function new_integrator(integer rid, atom interval)
    x = append(x,repeat(0,ISIZE))
    integer dx = length(x)
    x[dx][TERMINATE] = false
    x[dx][INTERVAL] = interval
    x[dx][KFUN] = rid
    x[dx][T0] = time()
    update(dx)
    x[dx][ID] = create_thread(tick,{dx})
    return dx
end function

procedure set_input(integer dx, rid)
    enter_cs(xlock)
    x[dx][KFUN] = rid
    x[dx][K0] = 0
    leave_cs(xlock)
end procedure

function get_output(integer dx)
    enter_cs(xlock)
    atom v = x[dx][VALUE]
    leave_cs(xlock)
    return v
end function

procedure stop_integrator(integer dx)
    x[dx][TERMINATE] = true
    wait_thread(x[dx][ID])
end procedure

puts(1,"")
integer dx = new_integrator(sine,0.01)
sleep(2) 
printf(1,"%f\n",get_output(dx))
set_input(dx,zero)
sleep(0.5)
printf(1,"%f\n",get_output(dx))
stop_integrator(dx)
Output:
-0.00326521
0.00196980

PicoLisp

(load "@lib/math.l")

(class +Active)
# inp val sum usec

(dm T ()
   (unless (assoc -100 *Run)           # Install timer task
      (task -100 100                   # Update objects every 0.1 sec
         (mapc 'update> *Actives) ) )
   (=: inp '((U) 0))                   # Set zero input function
   (=: val 0)                          # Initialize last value
   (=: sum 0)                          # Initialize sum
   (=: usec (usec))                    # and time
   (push '*Actives This) )             # Install in notification list

(dm input> (Fun)
   (=: inp Fun) )

(dm update> ()
   (let (U (usec)  V ((: inp) U))      # Get current time, calculate value
      (inc (:: sum)
         (*/
            (+ V (: val))              # (K(t[1]) + K(t[0])) *
            (- U (: usec))             # (t[1] - t[0]) /
            2.0 ) )                    # 2.0
      (=: val V)
      (=: usec U) ) )

(dm output> ()
   (format (: sum) *Scl) )             # Get result

(dm stop> ()
   (unless (del This '*Actives)        # Removing the last active object?
      (task -100) ) )                  # Yes: Uninstall timer task

(de integrate ()                       # Test it
   (let Obj (new '(+Active))           # Create an active object
      (input> Obj                      # Set input function
         '((U) (sin (*/ pi U 1.0))) )  # to sin(π * t)
      (wait 2000)                      # Wait 2 sec
      (input> Obj '((U) 0))            # Reset input function
      (wait 500)                       # Wait 0.5 sec
      (prinl "Output: " (output> Obj)) # Print return value
      (stop> Obj) ) )                  # Stop active object

PureBasic

Using the open-source precompiler SimpleOOP.

Prototype.d ValueFunction(f.d, t.d)

Class IntegralClass
  Time0.i
  Mutex.i
  S.d
  Freq.d
  Thread.i
  Quit.i
  *func.ValueFunction
  
  Protect Method Sampler()
    Repeat
      Delay(1)
      If This\func And This\Mutex
        LockMutex(This\Mutex)
        This\S + This\func(This\Freq, ElapsedMilliseconds()-This\Time0)
        UnlockMutex(This\Mutex)
      EndIf
    Until This\Quit 
  EndMethod
  
  BeginPublic
    Method Input(*func.ValueFunction)
      LockMutex(This\Mutex)
      This\func = *func
      UnlockMutex(This\Mutex)
    EndMethod
    
    Method.d Output()
      Protected Result.d
      LockMutex(This\Mutex)
      Result = This\S
      UnlockMutex(This\Mutex)
      MethodReturn Result
    EndMethod
    
    Method Init(F.d, *f)
      This\Freq   = F
      This\func   = *f
      This\Mutex  = CreateMutex()
      This\Time0  = ElapsedMilliseconds()
      This\Thread = CreateThread(This\Sampler, This)
      ThreadPriority(This\Thread, 10)
    EndMethod
    
    Method Release()
      This\Quit = #True
      WaitThread(This\Thread)
    EndMethod
  EndPublic
  
EndClass

;- Procedures for generating values
Procedure.d n(f.d, t.d)
  ; Returns nothing
EndProcedure

Procedure.d f(f.d, t.d)
  ; Returns the function of this task
  ProcedureReturn Sin(2*#PI*f*t)
EndProcedure

;- Test Code
*a.IntegralClass = NewObject.IntegralClass(0.5, @n()) ; Create the AO
*a\Input(@f()) ; Start sampling function f()
Delay(2000)    ; Delay 2 sec
*a\Input(@n()) ; Change to sampling 'nothing'
Delay( 500)    ; Wait 1/2 sec
MessageRequester("Info", StrD(*a\Output()))           ; Present the result
*a= FreeObject

Python

Works with: Python version 3

Assignment is thread-safe in Python, so no extra locks are needed in this case.


from time import time, sleep
from threading import Thread

class Integrator(Thread):
    'continuously integrate a function `K`, at each `interval` seconds'
    def __init__(self, K=lambda t:0, interval=1e-4):
        Thread.__init__(self)
        self.interval  = interval
        self.K   = K
        self.S   = 0.0
        self.__run = True
        self.start()

    def run(self):
        "entry point for the thread"
        interval = self.interval
        start = time()
        t0, k0 = 0, self.K(0)
        while self.__run:
            sleep(interval)
            t1 = time() - start
            k1 = self.K(t1)
            self.S += (k1 + k0)*(t1 - t0)/2.0
            t0, k0 = t1, k1

    def join(self):
        self.__run = False
        Thread.join(self)

if __name__ == "__main__":
    from math import sin, pi
 
    ai = Integrator(lambda t: sin(pi*t))
    sleep(2)
    print(ai.S)
    ai.K = lambda t: 0
    sleep(0.5)
    print(ai.S)

Racket

#lang racket

(require (only-in racket/gui sleep/yield timer%))

(define active%
  (class object%
    (super-new)
    (init-field k) ; input function
    (field [s 0])  ; state
    (define t_0 0)

    (define/public (input new-k) (set! k new-k))
    (define/public (output) s)

    (define (callback)
      (define t_1 (/ (- (current-inexact-milliseconds) start) 1000))
      (set! s (+ s (* (+ (k t_0) (k t_1))
                      (/ (- t_1 t_0) 2))))
      (set! t_0 t_1))

    (define start (current-inexact-milliseconds))
    (new timer%
         [interval 1000]
         [notify-callback callback])))

(define active (new active% [k (λ (t) (sin (* 2 pi 0.5 t)))]))
(sleep/yield 2)
(send active input (λ _ 0))
(sleep/yield 0.5)
(displayln (send active output))

Raku

(formerly Perl 6)

Works with: Rakudo version 2018.12

There is some jitter in the timer, but it is typically accurate to within a few thousandths of a second.

class Integrator {
    has $.f is rw = sub ($t) { 0 };
    has $.now is rw;
    has $.value is rw = 0;
    has $.integrator is rw;

    method init() {
        self.value = &(self.f)(0);
        self.integrator = Thread.new(
            :code({
                loop {
                    my $t1 = now;
                    self.value += (&(self.f)(self.now) + &(self.f)($t1)) * ($t1 - self.now) / 2;
                    self.now = $t1;
                    sleep .001;
                }
            }),
            :app_lifetime(True)
        ).run
    }

    method Input (&f-of-t) {
        self.f = &f-of-t;
        self.now = now;
        self.init;
    }

    method Output { self.value }
}

my $a = Integrator.new;

$a.Input( sub ($t) { sin(2 * π * .5 * $t) } );

say "Initial value: ", $a.Output;

sleep 2;

say "After 2 seconds: ", $a.Output;

$a.Input( sub ($t) { 0 } );

sleep .5;

say "f(0): ", $a.Output;
Typical output:
Initial value: 0
After 2 seconds: -0.0005555887464620366
f(0): 0

Rust

#![feature(mpsc_select)]

extern crate num;
extern crate schedule_recv;

use num::traits::Zero;
use num::Float;
use schedule_recv::periodic_ms;
use std::f64::consts::PI;
use std::ops::Mul;
use std::sync::mpsc::{self, SendError, Sender};
use std::sync::{Arc, Mutex};
use std::thread;
use std::time::Duration;

pub type Actor<S> = Sender<Box<Fn(u32) -> S + Send>>;
pub type ActorResult<S> = Result<(), SendError<Box<Fn(u32) -> S + Send>>>;

/// Rust supports both shared-memory and actor models of concurrency, and the `Integrator` utilizes
/// both.  We use an `Actor` to send the `Integrator` new functions, while we use a `Mutex`
/// (shared-memory concurrency) to hold the result of the integration.
///
/// Note that these are not the only options here--there are many, many ways you can deal with
/// concurrent access.  But when in doubt, a plain old `Mutex` is often a good bet.  For example,
/// this might look like a good situation for a `RwLock`--after all, there's no reason for a read
/// in the main task to block writes.  Unfortunately, unless you have significantly more reads than
/// writes (which is certainly not the case here), a `Mutex` will usually outperform a `RwLock`.
pub struct Integrator<S: 'static, T: Send> {
    input: Actor<S>,
    output: Arc<Mutex<T>>,
}

/// In Rust, time durations are strongly typed.  This is usually exactly what you want, but for a
/// problem like this--where the integrated value has unusual (unspecified?) units--it can actually
/// be a bit tricky.  Right now, `Duration`s can only be multiplied or divided by `i32`s, so in
/// order to be able to actually do math with them we say that the type parameter `S` (the result
/// of the function being integrated) must yield `T` (the type of the integrated value) when
/// multiplied by `f64`.  We could possibly replace `f64` with a generic as well, but it would make
/// things a bit more complex.
impl<S, T> Integrator<S, T>
where
    S: Mul<f64, Output = T> + Float + Zero,
    T: 'static + Clone + Send + Float,
{
    pub fn new(frequency: u32) -> Integrator<S, T> {
        // We create a pipe allowing functions to be sent from tx (the sending end) to input (the
        // receiving end).  In order to change the function we are integrating from the task in
        // which the Integrator lives, we simply send the function through tx.
        let (tx, input) = mpsc::channel();
        // The easiest way to do shared-memory concurrency in Rust is to use atomic reference
        // counting, or Arc, around a synchronized type (like Mutex<T>).  Arc gives you a guarantee
        // that memory will not be freed as long as there is at least one reference to it.
        // It is similar to C++'s shared_ptr, but it is guaranteed to be safe and is never
        // incremented unless explicitly cloned (by default, it is moved).
        let s: Arc<Mutex<T>> = Arc::new(Mutex::new(Zero::zero()));
        let integrator = Integrator {
            input: tx,
            // Here is the aforementioned clone.  We have to do it before s enters the closure,
            // because once that happens it is moved into the closure (and later, the new task) and
            // becomes inaccessible to the outside world.
            output: Arc::clone(&s),
        };
        thread::spawn(move || -> () {
            // The frequency is how often we want to "tick" as we update our integrated total.  In
            // Rust, timers can yield Receivers that are periodically notified with an empty
            // message (where the period is the frequency).  This is useful because it lets us wait
            // on either a tick or another type of message (in this case, a request to change the
            // function we are integrating).
            let periodic = periodic_ms(frequency);
            let mut t = 0;
            let mut k: Box<Fn(u32) -> S + Send> = Box::new(|_| Zero::zero());
            let mut k_0: S = Zero::zero();
            loop {
                // Here's the selection we talked about above.  Note that we are careful to call
                // the *non*-failing function, recv(), here.  The reason we do this is because
                // recv() will return Err when the sending end of a channel is dropped.  While
                // this is unlikely to happen for the timer (so again, you could argue for failure
                // there), it's normal behavior for the sending end of input to be dropped, since
                // it just happens when the Integrator falls out of scope.  So we handle it cleanly
                // and break out of the loop, rather than failing.
                select! {
                    res = periodic.recv() => match res {
                        Ok(_) => {
                            t += frequency;
                            let k_1: S = k(t);
                            // Rust Mutexes are a bit different from Mutexes in many other
                            // languages, in that the protected data is actually encapsulated by
                            // the Mutex.  The reason for this is that Rust is actually capable of
                            // enforcing (via its borrow checker) the invariant that the contents
                            // of a Mutex may only be read when you have acquired its lock.  This
                            // is enforced by way of a MutexGuard, the return value of lock(),
                            // which implements some special traits (Deref and DerefMut) that allow
                            // access to the inner element "through" the guard.  The element so
                            // acquired has a lifetime bounded by that of the MutexGuard, the
                            // MutexGuard can only be acquired by taking a lock, and the only way
                            // to release the lock is by letting the MutexGuard fall out of scope,
                            // so it's impossible to access the data incorrectly.  There are some
                            // additional subtleties around the actual implementation, but that's
                            // the basic idea.
                            let mut s = s.lock().unwrap();
                            *s = *s + (k_1 + k_0) * (f64::from(frequency) / 2.);
                            k_0 = k_1;
                        }
                        Err(_) => break,
                    },
                    res = input.recv() => match res {
                        Ok(k_new) => k = k_new,
                        Err(_) => break,
                    }
                }
            }
        });
        integrator
    }

    pub fn input(&self, k: Box<Fn(u32) -> S + Send>) -> ActorResult<S> {
        // The meat of the work is done in the other thread, so to set the
        // input we just send along the Sender we set earlier...
        self.input.send(k)
    }

    pub fn output(&self) -> T {
        // ...and to read the input, we simply acquire a lock on the output Mutex and return a
        // copy. Why do we have to copy it?  Because, as mentioned above, Rust won't let us
        // retain access to the interior of the Mutex unless we have possession of its lock.  There
        // are ways and circumstances in which one can avoid this (e.g. by using atomic types) but
        // a copy is a perfectly reasonable solution as well, and a lot easier to reason about :)
        *self.output.lock().unwrap()
    }
}

/// This function is fairly straightforward.  We create the integrator, set its input function k(t)
/// to 2pi * f * t, and then wait as described in the Rosetta stone problem.
fn integrate() -> f64 {
    let object = Integrator::new(10);
    object
        .input(Box::new(|t: u32| {
            let two_seconds_ms = 2 * 1000;
            let f = 1. / f64::from(two_seconds_ms);
            (2. * PI * f * f64::from(t)).sin()
        }))
        .expect("Failed to set input");
    thread::sleep(Duration::from_secs(2));
    object.input(Box::new(|_| 0.)).expect("Failed to set input");
    thread::sleep(Duration::from_millis(500));
    object.output()
}

fn main() {
    println!("{}", integrate());
}

/// Will fail on a heavily loaded machine
#[test]
#[ignore]
fn solution() {
    // We should just be able to call integrate, but can't represent the closure properly due to
    // rust-lang/rust issue #17060 if we make frequency or period a variable.
    // FIXME(pythonesque): When unboxed closures are fixed, fix integrate() to take two arguments.
    let object = Integrator::new(10);
    object
        .input(Box::new(|t: u32| {
            let two_seconds_ms = 2 * 1000;
            let f = 1. / (two_seconds_ms / 10) as f64;
            (2. * PI * f * t as f64).sin()
        }))
        .expect("Failed to set input");
    thread::sleep(Duration::from_millis(200));
    object.input(Box::new(|_| 0.)).expect("Failed to set input");
    thread::sleep(Duration::from_millis(100));
    assert_eq!(object.output() as u32, 0)
}

Scala

object ActiveObject {

  class Integrator {
    
    import java.util._
    import scala.actors.Actor._

    case class Pulse(t: Double)
    case class Input(k: Double => Double)
    case object Output
    case object Bye

    val timer = new Timer(true)
    var k: Double => Double = (_ => 0.0)
    var s: Double = 0.0
    var t0: Double = 0.0

    val handler = actor {
      loop {
        react {
          case Pulse(t1) => s += (k(t1) + k(t0)) * (t1 - t0) / 2.0; t0 = t1
          case Input(k) => this.k = k
          case Output => reply(s)
          case Bye => timer.cancel; exit
        }
      }
    }

    timer.scheduleAtFixedRate(new TimerTask {
      val start = System.currentTimeMillis
      def run { handler ! Pulse((System.currentTimeMillis - start) / 1000.0) }
    }, 0, 10) // send Pulse every 10 ms

    def input(k: Double => Double) = handler ! Input(k)
    def output = handler !? Output
    def bye = handler ! Bye
  }

  def main(args: Array[String]) {
    val integrator = new Integrator
    integrator.input(t => Math.sin(2.0 * Math.Pi * 0.5 * t))
    Thread.sleep(2000)
    integrator.input(_ => 0.0)
    Thread.sleep(500)
    println(integrator.output)
    integrator.bye
  }
}

Smalltalk

Object subclass:#Integrator
        instanceVariableNames:'tickRate input s thread'
        classVariableNames:''
        poolDictionaries:''
        category:'Rosetta'

instance methods:

input:aFunctionOfT
    input := aFunctionOfT.

startWithTickRate:r
    "setup and start sampling"
    tickRate := r.
    s := 0.    
    thread := [ self integrateLoop ] fork.

stop
    "stop and return the 'final' output"
    thread terminate.
    ^ s

integrateLoop
    "no need for any locks 
     - the assignment to s is atomic in Smallalk; its either done or not, when terminated, so who cares"

    |tBegin tPrev tNow kPrev kNow deltaT delta|

    tBegin := tPrev := Timestamp nowWithMilliseconds.
    kPrev := input value:0.

    [true] whileTrue:[
        Delay waitForSeconds: tickRate.
        tNow := Timestamp nowWithMilliseconds.
        kNow := input value:(tNow millisecondDeltaFrom:tBegin) / 1000.

        deltaT := (tNow millisecondDeltaFrom:tPrev) / 1000.
        delta := (kPrev + kNow) * deltaT / 2.

        s := s + delta.
        tPrev := tNow. kPrev := kNow.
    ].

class methods:

example
    #( 0.5 0.1 0.05 0.01 0.005 0.001 0.0005 ) do:[:sampleRate |
        |i|

        i := Integrator new.
        i input:[:t | (2 * Float pi * 0.5 * t) sin].
        i startWithTickRate:sampleRate.

        Delay waitForSeconds:2.
        i input:[:t | 0].
        Delay waitForSeconds:0.5.

        Transcript 
            show:'Sample rate: '; showCR:sampleRate; 
            showCR:(i stop).
    ].

running:

Integrator example

output:

Sample rate: 0.5
-0.0258202058271805
Sample rate: 0.1
-0.00519217893508676
Sample rate: 0.05
-0.000897807957672559
Sample rate: 0.01
-0.000650159409949159
Sample rate: 0.005
-0.00033633922519125
Sample rate: 0.001
0.000286557714782226
Sample rate: 0.0005
0.000253571129723327

for backward compatibility, the smalltalk used here returns only timestamps with second-precision from "Timestamp now". Therefore, the millisecond-precision variant was used here. An alternative would have been to ask the OS for its ticker, which is more precise.

SuperCollider

Instead of writing a class, here we just use an environment to encapsulate state.

(
a = TaskProxy { |envir|
	envir.use {
		~integral = 0;
		~time = 0;
		~prev = 0;
		~running = true;
		loop {
			~val = ~input.(~time);
			~integral = ~integral + (~val + ~prev * ~dt / 2);
			~prev = ~val;
			~time = ~time + ~dt;
			~dt.wait;
		}
	}
};
)

// run the test 
(
fork {
	a.set(\dt, 0.0001);
	a.set(\input, { |t| sin(2pi * 0.5 * t) });
	a.play(quant: 0); // play immediately
	2.wait;
	a.set(\input, 0);
	0.5.wait;
	a.stop;
	a.get(\integral).postln; // answers -7.0263424372343e-15
}
)

Swift

// For NSObject, NSTimeInterval and NSThread
import Foundation
// For PI and sin
import Darwin

class ActiveObject:NSObject {

    let sampling = 0.1
    var K: (t: NSTimeInterval) -> Double
    var S: Double
    var t0, t1: NSTimeInterval
    var thread = NSThread()
    
    func integrateK() {
        t0 = t1
        t1 += sampling
        S += (K(t:t1) + K(t: t0)) * (t1 - t0) / 2
    }

    func updateObject() {
        while true {
            integrateK()
            usleep(100000)
        }
    }
    
    init(function: (NSTimeInterval) -> Double) {
        S = 0
        t0 = 0
        t1 = 0
        K = function
        super.init()
        thread = NSThread(target: self, selector: "updateObject", object: nil)
        thread.start()
    }
    
    func Input(function: (NSTimeInterval) -> Double) {
        K = function

    }
    
    func Output() -> Double {
        return S
    }
    
}

// main
func sine(t: NSTimeInterval) -> Double {
    let f = 0.5
    
    return sin(2 * M_PI * f * t)
}

var activeObject = ActiveObject(function: sine)

var date = NSDate()

sleep(2)

activeObject.Input({(t: NSTimeInterval) -> Double in return 0.0})

usleep(500000)

println(activeObject.Output())

Sample output:

1.35308431126191e-16

Tcl

Works with: Tcl version 8.6

or

Library: TclOO

This implementation Tcl 8.6 for object support (for the active integrator object) and coroutine support (for the controller task). It could be rewritten to only use 8.5 plus the TclOO library.

package require Tcl 8.6
oo::class create integrator {
    variable e sum delay tBase t0 k0 aid
    constructor {{interval 1}} {
	set delay $interval
	set tBase [clock microseconds]
	set t0 0
	set e { 0.0 }
	set k0 0.0
	set sum 0.0
	set aid [after $delay [namespace code {my Step}]]
    }
    destructor {
	after cancel $aid
    }
    method input expression {
	set e $expression
    }
    method output {} {
	return $sum
    }
    method Eval t {
	expr $e
    }
    method Step {} {
	set aid [after $delay [namespace code {my Step}]]
	set t [expr {([clock microseconds] - $tBase) / 1e6}]
	set k1 [my Eval $t]
	set sum [expr {$sum + ($k1 + $k0) * ($t - $t0) / 2.}]
	set t0 $t
	set k0 $k1
    }
}

set pi 3.14159265
proc pause {time} {
    yield [after [expr {int($time * 1000)}] [info coroutine]]
}
proc task {script} {
    coroutine task_ apply [list {} "$script;set ::done ok"]
    vwait done
}
task {
    integrator create i
    i input {sin(2*$::pi * 0.5 * $t)}
    pause 2
    i input { 0.0 }
    pause 0.5
    puts [format %.15f [i output]]
}

Sample output:

-0.000000168952702

Visual Basic .NET

Since this object is CPU intensive, shutting it down when done is crucial. To facilitate this, the IDisposable pattern was used.

Module Module1
 
    Sub Main()
        Using active As New Integrator
            active.Operation = Function(t As Double) Math.Sin(2 * Math.PI * 0.5 * t)
            Threading.Thread.Sleep(TimeSpan.FromSeconds(2))
            Console.WriteLine(active.Value)
            active.Operation = Function(t As Double) 0
            Threading.Thread.Sleep(TimeSpan.FromSeconds(0.5))
            Console.WriteLine(active.Value)
        End Using
        Console.ReadLine()
    End Sub
 
End Module
  
Class Integrator
    Implements IDisposable
 
    Private m_Operation As Func(Of Double, Double)
    Private m_Disposed As Boolean
    Private m_SyncRoot As New Object
    Private m_Value As Double
 
    Public Sub New()
        m_Operation = Function(void) 0.0
        Dim t As New Threading.Thread(AddressOf MainLoop)
        t.Start()
    End Sub
 
    Private Sub MainLoop()
        Dim epoch = Now
        Dim t0 = 0.0
        Do
            SyncLock m_SyncRoot
                Dim t1 = (Now - epoch).TotalSeconds
                m_Value = m_Value + (Operation(t1) + Operation(t0)) * (t1 - t0) / 2
                t0 = t1
            End SyncLock
            Threading.Thread.Sleep(10)
        Loop Until m_Disposed
    End Sub
 
    Public Property Operation() As Func(Of Double, Double)
        Get
            SyncLock m_SyncRoot
                Return m_Operation
            End SyncLock
        End Get
        Set(ByVal value As Func(Of Double, Double))
            SyncLock m_SyncRoot
                m_Operation = value
            End SyncLock
        End Set
    End Property
 
    Public ReadOnly Property Value() As Double
        Get
            SyncLock m_SyncRoot
                Return m_Value
            End SyncLock
        End Get
    End Property
 
    Protected Overridable Sub Dispose(ByVal disposing As Boolean)
        m_Disposed = True
    End Sub
 
    Public Sub Dispose() Implements IDisposable.Dispose
        Dispose(True)
        GC.SuppressFinalize(Me)
    End Sub
 
End Class


Output: 0.000241446762282308

Wren

Wren doesn't have threads but does have fibers which are cooperatively (rather than preemptively) scheduled. Only one fiber can run at a time.

However, it is possible to perform asynchronous operations in Wren-cli using a combination of the Scheduler and Timer classes which use the C library libuv under the hood. The problem is that, due to a bug, the Timer.sleep method doesn't just pause the current fiber, it also pauses the System.clock method! So we can't use the latter to measure time here.

What I've done instead is to pre-compute the number of updates performed on my machine for a given function and time period which is a fairly stable figure (though it will obviously be different on other machines). I've then used this figure to measure elapsed time for each update. On average this gives results of around 0.003 seconds which I consider acceptable in the circumstances.

import "scheduler" for Scheduler
import "timer" for Timer

var Interval = 0

class Integrator {
    construct new() {
        _sum = 0
    }

    input(k) {
        _k = k
        _v0 = k.call(0)
        _t = 0
        _running = true
        integrate_()
    }

    output { _sum }

    stop() {
        _running = false
    }

    integrate_() {
        while (_running) {
            Timer.sleep(1)
            update_()
        }
    }

    update_() {
        _t = _t + Interval
        var v1 = _k.call(_t)
        var trap = Interval * (_v0 + v1) / 2
        _sum = _sum + trap
        _v0 = v1
    }
}

var integrator = Integrator.new()
Scheduler.add {
    Interval = 2 / 1550  // machine specific value
    integrator.input(Fn.new { |t| (Num.pi * t).sin })
}
Timer.sleep(2000)

Scheduler.add {
    Interval = 0.5 / 775 // machine specific value
    integrator.input(Fn.new { |t| 0 })
}
Timer.sleep(500)

integrator.stop()
System.print(integrator.output)
Output:
0.0028437802254386

zkl

Translation of: Python

Uses cheese ball thread safety: since the integrator runs continuously and I don't want to queue the output, just sample it, strong references are used as they change atomically.

class Integrator{
   // continuously integrate a function `K`, at each `interval` seconds'
   fcn init(f,interval=1e-4){
      var _interval=interval, K=Ref(f), S=Ref(0.0), run=True;
      self.launch();  // start me as a thread
   }
   fcn liftoff{ // entry point for the thread
      start:=Time.Clock.timef;  // floating point seconds since Epoch
      t0,k0,s:=0,K.value(0),S.value;
      while(run){
	 Atomic.sleep(_interval);
	 t1,k1:=Time.Clock.timef - start, K.value(t1);
	 s+=(k1 + k0)*(t1 - t0)/2.0; S.set(s);
	 t0,k0=t1,k1;
      }
   }
   fcn sample  { S.value  }
   fcn setF(f) { K.set(f) }
}
ai:=Integrator(fcn(t){ ((0.0).pi*t).sin() });
Atomic.sleep(2);
ai.sample().println();

ai.setF(fcn{ 0 });
Atomic.sleep(0.5);
ai.sample().println();
Output:
4.35857e-09
1.11571e-07