Events: Difference between revisions
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{{task|Concurrency}}{{requires|Concurrency}}[[Category:Encyclopedia]]
'''Event''' is a synchronization object. An event has two states ''signaled'' and ''reset''. A [[task]] may await for the event to enter the desired state, usually the ''signaled'' state. It is released once the state is entered. Releasing waiting tasks is called ''event notification''. Programmatically controlled events can be set by a [[task]] into one of its states.
Line 7 ⟶ 5:
* ''internal'', from another [[task]], programmatically;
* ''external'', from the hardware, such as user input, timer, etc. Signaling an event from the hardware is accomplished by means
Event is a low-level synchronization mechanism. It neither identify the state that caused it signaled, nor the source of, nor who is the subject of notification. Events augmented by data and/or publisher-subscriber schemes are often referred as '''messages''', '''signals''' etc.
Line 13 ⟶ 11:
In the context of general programming '''event-driven architecture''' refers to a design that deploy events in order to synchronize [[task]]s with the asynchronous activities they must be aware of. The opposite approach is '''polling''' sometimes called '''busy waiting''', when the synchronization is achieved by an explicit periodic querying the state of the activity. As the name suggests busy waiting consumes system resources even when the external activity does not change its state.
Event-driven architectures are widely used in GUI design and SCADA systems. They are flexible and have relatively short response times. At the same time event-driven architectures suffer to the problems related to their unpredictability. They face [[race condition]], deadlocking, live locks and priority inversion. For this reason [[real-time computing|real-time]] systems tend to polling schemes, trading performance for predictability in the worst case scenario.
=Variants of events=
Line 24 ⟶ 22:
=Sample implementations / APIs=
Show how a manual-reset event can be implemented in the language or else use an API to a library that provides events. Write a program that waits 1s and then signals the event to a [[task]] waiting for the event.
=={{header|Ada}}==
[[Ada]] provides higher-level concurrency primitives, which are complete in the sense that they also allow implementations of the lower-level ones, like event. Here is an implementation of the manual-reset event.
The event interface:
<syntaxhighlight lang="ada">protected type Event is
procedure Signal;
procedure Reset;
Line 36 ⟶ 34:
private
Fired : Boolean := False;
end Event;</syntaxhighlight>
The event implementation:
<syntaxhighlight lang="ada">protected body Event is
procedure Signal is
begin
Line 53 ⟶ 49:
null;
end Wait;
end Event;</syntaxhighlight>
With the event defined above:
<syntaxhighlight lang="ada">with Ada.Text_IO; use Ada.Text_IO;
procedure Test_Events is
Line 74 ⟶ 68:
Put_Line ("Signal X");
X.Signal;
end Test_Events;</syntaxhighlight>
Sample output:
<pre>
Line 82 ⟶ 75:
A received X
</pre>
=={{header|AutoHotkey}}==
<syntaxhighlight lang="autohotkey">SetTimer, internal, 1000
Return
internal: ; fire on a timer
TrayTip, internal, internal event!`npress F2 for external event
SetTimer, internal, off
Return
F2:: ; external event: fire on F2 key press
TrayTip, external, f2 key pressed
Return</syntaxhighlight>
=={{header|BASIC256}}==
{{trans|Gambas}}
<syntaxhighlight lang="basic256">
subroutine Timer1_Timer()
print hour; ":"; minute; ":"; second
end subroutine
</syntaxhighlight>
{{out}}
<pre>
Igual que la entrada de Gambas.
</pre>
=={{header|BBC BASIC}}==
{{works with|BBC BASIC for Windows}}
===API===
This uses a Windows event object:
<syntaxhighlight lang="bbcbasic"> INSTALL @lib$+"TIMERLIB"
WAIT_TIMEOUT = 258
SYS "CreateEvent", 0, 1, 0, 0 TO hEvent%
timerID% = FN_ontimer(1000, PROCelapsed, 0)
PRINT "Waiting for event..."
REPEAT
SYS "WaitForSingleObject", hEvent%, 1 TO res%
UNTIL res% <> WAIT_TIMEOUT
PRINT "Event signalled"
END
DEF PROCelapsed
SYS "SetEvent", hEvent%
ENDPROC</syntaxhighlight>
===Native===
This uses a simple variable as a semaphore:
<syntaxhighlight lang="bbcbasic"> INSTALL @lib$+"TIMERLIB"
Event% = FALSE
timerID% = FN_ontimer(1000, PROCelapsed, 0)
PRINT "Waiting for event..."
REPEAT
WAIT 0
UNTIL Event%
PRINT "Event signalled"
END
DEF PROCelapsed
Event% = TRUE
ENDPROC</syntaxhighlight>
=={{header|C}}==
Using pipe to communicate to <code>fork</code>ed child. Since child will be blocking trying to read the other end of the pipe, this can be used for synchronization.
<syntaxhighlight lang="c">#include <stdio.h>
#include <unistd.h>
int main()
{
int p[2];
pipe(p);
if (fork()) {
close(p[0]);
sleep(1);
write(p[1], p, 1);
wait(0);
} else {
close(p[1]);
read(p[0], p + 1, 1);
puts("received signal from pipe");
}
return 0;
}</syntaxhighlight>
=={{header|C sharp|C#}}==
<syntaxhighlight lang="csharp">using System;
using System.Timers;
class Program
{
static void Main()
{
var timer = new Timer(1000);
timer.Elapsed += new ElapsedEventHandler(OnElapsed);
Console.WriteLine(DateTime.Now);
timer.Start();
Console.ReadLine();
}
static void OnElapsed(object sender, ElapsedEventArgs eventArgs)
{
Console.WriteLine(eventArgs.SignalTime);
((Timer)sender).Stop();
}
}</syntaxhighlight>
Sample output:
<pre>10-11-2010 18:35:11
10-11-2010 18:35:12</pre>
=={{header|Clojure}}==
{{trans|Go}}
<syntaxhighlight lang="lisp">(ns async-example.core
(:require [clojure.core.async :refer [>! <! >!! <!! go chan]])
(:require [clj-time.core :as time])
(:require [clj-time.format :as time-format])
(:gen-class))
;; Helper functions (logging & time stamp)
; Time stamp format
(def custom-formatter (time-format/formatter "yyyy:MM:dd:ss.SS"))
(defn safe-println [& more]
" This function avoids interleaving of text output when using println due to race condition for multi-processes printing
as discussed http://yellerapp.com/posts/2014-12-11-14-race-condition-in-clojure-println.html "
(.write *out* (str (clojure.string/join " " more) "\n")))
(defn log [s]
" Outputs mesage with time stamp "
(safe-println (time-format/unparse custom-formatter (time/now)) ":" s))
;; Main code
(defn -main [& args]
(let [c (chan)]
(log "Program start")
(go
(log "Task start")
(log (str "Event received by task: "(<! c))))
(<!!
(go
(log "program sleeping")
(Thread/sleep 1000) ; Wait 1 second
(log "Program signaling event")
(>! c "reset") ; Send message to task
))))
; Invoke -main function
(-main)
</syntaxhighlight>
{{Output}}
<pre>
2016:10:18:06.93 : Program start
2016:10:18:06.94 : task start
2016:10:18:06.94 : program sleeping
2016:10:18:07.94 : Program signaling event
2016:10:18:07.94 : Event received by task: reset
</pre>
=={{header|Delphi}}==
<syntaxhighlight lang="delphi">program Events;
{$APPTYPE CONSOLE}
uses
SysUtils, Classes, Windows;
type
TWaitThread = class(TThread)
private
FEvent: THandle;
public
procedure Sync;
procedure Execute; override;
constructor Create(const aEvent: THandle); reintroduce;
end;
{ TWaitThread }
constructor TWaitThread.Create(const aEvent: THandle);
begin
inherited Create(False);
FEvent := aEvent;
end;
procedure TWaitThread.Execute;
var
res: Cardinal;
begin
res := WaitForSingleObject(FEvent, INFINITE);
if res = 0 then
Synchronize(Sync);
end;
procedure TWaitThread.Sync;
begin
Writeln(DateTimeToStr(Now));
end;
var
event: THandle;
begin
Writeln(DateTimeToStr(Now));
event := CreateEvent(nil, False, False, 'Event');
with TWaitThread.Create(event) do
try
Sleep(1000);
SetEvent(event)
finally
Free;
end;
Readln;
end.</syntaxhighlight>
Sample output:
<pre>
09.08.2011 0:27:43
09.08.2011 0:27:44
</pre>
=={{header|E}}==
<syntaxhighlight lang="e">def makeEvent() {
def [var fired, var firer] := Ref.promise()
def event {
to signal() {
firer.resolveRace(null) # all current and future wait()s will resolve
}
to reset() {
if (firer.isDone()) { # ignore multiple resets. If we didn't, then
# reset() wait() reset() signal() would never
# resolve that wait().
# create all fresh state
def [p, r] := Ref.promise()
fired := p
firer := r
}
}
to wait() {
return fired
}
}
return event
}</syntaxhighlight>
The event object has this behavior: the return value of <code>.wait()</code> will be resolved after the time of the earliest <code>.signal()</code> for which there is no intervening <code>.reset()</code>.
<syntaxhighlight lang="e">def e := makeEvent()
{
when (e.wait()) -> {
println("[2] Received event.")
}
println("[2] Waiting for event...")
}
{
timer.whenPast(timer.now() + 1000, def _() {
println("[1] Signaling event.")
e.signal()
})
println("[1] Waiting 1 second...")
}</syntaxhighlight>
=={{header|EasyLang}}==
[https://easylang.dev/show/#cod=y89TKMnMTS3iUlBQyM0vS1UoSsxLyc9NU9BSMDQwQOWB1CRnFiXnpCoYgdhgjQqGXHpc+XlAzaXFqfEp+eV5cKMgQhVQuhJFux4XRLcBFwA= Run it]
<syntaxhighlight>
on timer
move randomf * 100 randomf * 100
circle 2
timer 1
.
on mouse_down
move mouse_x mouse_y
circle 2
.
timer 0
</syntaxhighlight>
=={{header|Elixir}}==
{{trans|Erlang}}
<syntaxhighlight lang="elixir">defmodule Events do
def log(msg) do
time = Time.utc_now |> to_string |> String.slice(0..7)
IO.puts "#{time} => #{msg}"
end
def task do
log("Task start")
receive do
:go -> :ok
end
log("Task resumed")
end
def main do
log("Program start")
{pid,ref} = spawn_monitor(__MODULE__,:task,[])
log("Program sleeping")
Process.sleep(1000)
log("Program signalling event")
send(pid, :go)
receive do
{:DOWN,^ref,_,_,_} -> :task_is_down
end
end
end
Events.main</syntaxhighlight>
{{out}}
<pre>
06:27:05 => Program start
06:27:05 => Program sleeping
06:27:05 => Task start
06:27:06 => Program signalling event
06:27:06 => Task resumed
</pre>
=={{header|Erlang}}==
Events can be implemented by using the selective receive expression and erlang's built in message passing. Here task waits for the message 'go' before it will continue.
<syntaxhighlight lang="erlang">
-module(events).
-compile(export_all).
log(Msg) ->
{H,M,S} = erlang:time(),
io:fwrite("~2.B:~2.B:~2.B => ~s~n",[H,M,S,Msg]).
task() ->
log("Task start"),
receive
go -> ok
end,
log("Task resumed").
main() ->
log("Program start"),
P = spawn(?MODULE,task,[]),
log("Program sleeping"),
timer:sleep(1000),
log("Program signalling event"),
P ! go,
timer:sleep(100).
</syntaxhighlight>
'''Output:'''
<syntaxhighlight lang="erlang">
66> events:main().
0: 0:57 => Program start
0: 0:57 => Program sleeping
0: 0:57 => Task start
0: 0:58 => Program signalling event
0: 0:58 => Task resumed
ok
</syntaxhighlight>
=={{header|F_Sharp|F#}}==
{{trans|C#}}
<syntaxhighlight lang="fsharp">open System
open System.Timers
let onElapsed (sender : obj) (eventArgs : ElapsedEventArgs) =
printfn "%A" eventArgs.SignalTime
(sender :?> Timer).Stop()
[<EntryPoint>]
let main argv =
let timer = new Timer(1000.)
timer.Elapsed.AddHandler(new ElapsedEventHandler(onElapsed))
printfn "%A" DateTime.Now
timer.Start()
ignore <| Console.ReadLine()
0</syntaxhighlight>
=={{header|FreeBASIC}}==
{{trans|Gambas}}
<syntaxhighlight lang="freebasic">
Sub Timer1_Timer()
Print Time
End Sub
</syntaxhighlight>
{{out}}
<pre>
Igual que la entrada de Gambas.
</pre>
=={{header|FutureBasic}}==
Event timer fires every tenth of a second
<syntaxhighlight lang="futurebasic">
timerbegin, 0.1, YES
cls : printf @"%@", time(@"h:mm:ss a zzz")
timerend
HandleEvents
</syntaxhighlight>
{{output}}
<pre>
4:44:36 PM EDT
</pre>
=={{header|Gambas}}==
<syntaxhighlight lang="gambas">Public Sub Timer1_Timer()
Print Str(Time(Now))
End</syntaxhighlight>
Output:
<pre>
16:14:18
16:14:19
16:14:20
16:14:21
16:14:22
16:14:23
16:14:24
16:14:25
</pre>
=={{header|Go}}==
A Go channel can represent an manual-reset event, as described by the task. The two states of signaled and reset correspond to the presence or absence of a value on the channel. The program signals by sending a value on the channel. The event is reset when the waiting task explicitly executes the channel receive operation, <-event.
<syntaxhighlight lang="go">package main
import (
"log"
"os"
"time"
)
func main() {
l := log.New(os.Stdout, "", log.Ltime | log.Lmicroseconds)
l.Println("program start")
event := make(chan int)
go func() {
l.Println("task start")
<-event
l.Println("event reset by task")
}()
l.Println("program sleeping")
time.Sleep(1 * time.Second)
l.Println("program signaling event")
event <- 0
time.Sleep(100 * time.Millisecond)
}</syntaxhighlight>
{{out}}
<pre>
01:27:21.862000 program start
01:27:21.862245 program sleeping
01:27:21.867269 task start
01:27:22.868294 program signaling event
01:27:22.868346 event reset by task
</pre>
=={{header|Haskell}}==
<syntaxhighlight lang="haskell">import Control.Concurrent (threadDelay, forkIO)
import Control.Concurrent.SampleVar
-- An Event is defined as a SampleVar with no data.
-- http://haskell.org/ghc/docs/latest/html/libraries/base/Control-Concurrent-SampleVar.html
newtype Event = Event (SampleVar ())
newEvent = fmap Event (newEmptySampleVar)
signalEvent (Event sv) = writeSampleVar sv ()
resetEvent (Event sv) = emptySampleVar sv
waitEvent (Event sv) = readSampleVar sv</syntaxhighlight>
<syntaxhighlight lang="haskell">main = do e <- newEvent
forkIO (waitTask e)
putStrLn "[1] Waiting 1 second..."
threadDelay 1000000 {- µs -}
putStrLn "[1] Signaling event."
signalEvent e
threadDelay 1000000 {- µs -} -- defer program exit for reception
waitTask e = do putStrLn "[2] Waiting for event..."
waitEvent e
putStrLn "[2] Received event."</syntaxhighlight>
Note: Because there is no serialization of the text output, there is a chance that it will appear interleaved.
==Icon and {{header|Unicon}}==
The following only works in Unicon. The example illustrates the multiple tasks can
receive the same event:
<syntaxhighlight lang="unicon">record Event(cond, value)
procedure main()
event := Event(condvar())
t1 := thread {
write("Task one waiting for event....")
critical event.cond: while /(event.value) do wait(event.cond)
write("Task one received event.")
}
t2 := thread {
write("Task two waiting for event....")
critical event.cond: while /(event.value) do wait(event.cond)
write("Task two received event.")
}
delay(1000) # Let main thread post the event.
event.value := "yes"
write("Signalling event.")
signal(event.cond,0)
every wait(t1|t2)
end</syntaxhighlight>
Sample run:
<pre>
->event
Task two waiting for event....
Task one waiting for event....
Signalling event.
Task two received event.
Task one received event.
->
</pre>
=={{header|JavaScript}}==
An example using the [[wp:Yahoo!_UI_Library|YUI]] library:
<syntaxhighlight lang="javascript">YUI().use('event-custom', function(Y) {
// add a custom event:
Y.on('my:event', function () {
alert("Event fired");
});
// fire the event after one second:
setTimeout(function () {
Y.fire('my:event');
}, 1000);
});</syntaxhighlight>
An example simulating [[wp:Document_Object_Model|DOM]] events:
<syntaxhighlight lang="javascript">YUI().use('node-event-simulate', function(Y) {
// add a click event handler to a DOM node with id "button":
Y.one("#button").on("click", function (e) {
alert("Button clicked");
});
// simulate the click after one second:
setTimeout(function () {
Y.one("#button").simulate("click");
}, 1000);
});</syntaxhighlight>
=={{header|Julia}}==
Julia provides a variety of high and low level functions and macros for multitasking and events.
The code below uses a Condition() event semaphore created in the base thread for communication
between two child threads.
<syntaxhighlight lang="julia">
function dolongcomputation(cond)
det(rand(4000, 4000))
Base.notify(cond)
end
function printnotice(cond)
Base.wait(cond)
println("They are finished.")
end
function delegate()
println("Starting task, sleeping...")
condition = Base.Condition()
Base.@async(printnotice(condition))
Base.@async(dolongcomputation(condition))
end
delegate()
sleep(5)
println("Done sleeping.")
</syntaxhighlight>
{{output}}<pre>
Starting task, sleeping...
They are finished.
Done sleeping.
</pre>
=={{header|LFE}}==
{{trans|Erlang}}
Paste in the REPL:
<syntaxhighlight lang="lisp">
(defun log (msg)
(let ((`#(,h ,m ,s) (erlang:time)))
(lfe_io:format "~2.B:~2.B:~2.B => ~s~n" `(,h ,m ,s ,msg))))
(defun task ()
(log "Task start")
(receive
('go 'ok))
(log "Task resumed"))
(defun run ()
(log "Program start")
(let ((pid (spawn (lambda () (task)))))
(progn
(log "Program sleeping")
(timer:sleep 1000)
(log "Program signalling event")
(! pid 'go)
(timer:sleep 100))))
</syntaxhighlight>
Usage:
<pre>
> (run)
18:34:53 => Program start
18:34:53 => Program sleeping
18:34:53 => Task start
18:34:54 => Program signalling event
18:34:54 => Task resumed
ok
</pre>
OTP comes with a <code>gen_even</code>t behavior that is more robust and resilient than this version. That is what should be used for any non-toy example or project.
=={{header|Lingo}}==
Lingo/Director uses (stateless) events for system/application state change notifications, user action notifications and inter-sprite communication.
To catch an event, a corresponding event handler - a function with a predefined name - has to be definined in the code. Examples for such event handlers are:
<syntaxhighlight lang="lingo">-- the current window was closed
on closeWindow
...
end
-- the left mouse button was pressed by the user
on mouseDown
...
end</syntaxhighlight>
Also "Sprites" (visual elements) receive events by setting up such event handlers in scripts attached to them. Both predefined and custom events can be sent programmatically to sprites, e.g. using:
<syntaxhighlight lang="lingo">-- send event #mouseDown programmatically to sprite 1
sendSprite(1, #mouseDown)
-- send custom event #foo to named sprite "bar"
sendSprite("bar", #foo)
-- send custom event #fooBar to all existing sprites
sendAllSprites(#fooBar)</syntaxhighlight>
Using a binary plugin ("Xtra"), in Windows also lower level window messages can be both sent and received:
{{libheader|Msg Xtra}}
<syntaxhighlight lang="lingo">mx = xtra("Msg").new()
-- send message WM_LBUTTONDOWN to a specific window identified by HWND hwnd
WM_LBUTTONDOWN = 513
MK_LBUTTON = 1
lParam = 65536*y + x
mx.send_msg (hwnd, WM_LBUTTONDOWN, MK_LBUTTON, lParam)
-- listen for WM_COPYDATA and WM_MOUSEWHEEL messages sent to current application
-- window, notify Lingo callback function 'msgReceived' when such messages occur.
-- This callback function will receive hwnd, message, wParam and lParam as arguments
-- (and for WM_COPYDATA messages also the data that was sent as ByteArray).
WM_COPYDATA = 74
WM_MOUSEWHEEL = 522
mx.msg_listen([WM_COPYDATA, WM_MOUSEWHEEL], VOID, #msgReceived)</syntaxhighlight>
=={{header|Mathematica}}/{{header|Wolfram Language}}==
Mathematica supports events from timers (via Pause[]), task schedule descriptors. This will print a message after 4 seconds, then terminate the program.
<syntaxhighlight lang="mathematica">Print["Will exit in 4 seconds"]; Pause[4]; Quit[]
->Will exit in 4 seconds</syntaxhighlight>
=={{header|Nim}}==
{{trans|C}}
<syntaxhighlight lang="nim">import posix
var p: array[2, cint]
discard pipe p
if fork() > 0:
discard close p[0]
discard sleep 1
discard p[1].write(addr p[0], 1)
var x: cint = 0
discard wait (addr x)
else:
discard close p[1]
discard p[0].read(addr p[1], 1)
echo "received signal from pipe"</syntaxhighlight>
===Stdlib Semaphore===
This version using locks module for signaling the condition.
<syntaxhighlight lang="nim">import locks
from os import sleep
import times
from strformat import fmt
var
# condition variable which shared across threads
cond: Cond
lock: Lock
threadproc: Thread[void]
proc waiting {.thread.} =
echo "spawned waiting proc"
let start = getTime()
cond.wait lock
echo fmt"thread ended after waiting {getTime() - start}."
proc main =
initCond cond
initLock lock
threadproc.createThread waiting
echo "in main proc"
os.sleep 1000
echo "send signal/event notification"
signal cond
joinThread threadproc
deinitCond cond
deinitLock lock
main()</syntaxhighlight>
Compile and run: <pre>nim c -r --threads:on events_cond.nim</pre>
{{out}}
<pre>in main proc
spawned waiting proc
send signal/event notification
thread ended after waiting 1 second, 61 microseconds, and 311 nanoseconds.</pre>
=={{header|Oforth}}==
An event is often implemented with a control channel. A task is waiting for an object on the channel. When the event occurs, another task sends an object on this channel.
<syntaxhighlight lang="oforth">: anEvent
| ch |
Channel new ->ch
#[ ch receive "Ok, event is signaled !" println ] &
System sleep(1000)
ch send($myEvent) ;</syntaxhighlight>
An emitter is a general implementation for handling events : an emitter waits for events emitted and launches listeners that are waiting for those events.
<syntaxhighlight lang="oforth">import: emitter
: anEvent2
| e i |
Emitter new(null) ->e
e onEvent($myEvent, #[ "Event is signaled !" println ])
10 loop: i [
1000 System sleep
$myEvent e emit
]
e close ;</syntaxhighlight>
=={{header|Oz}}==
{{trans|Haskell}}
Events can be implemented as mutable references to dataflow variables:
<syntaxhighlight lang="oz">declare
fun {NewEvent}
{NewCell _}
end
proc {SignalEvent Event}
@Event = unit
end
proc {ResetEvent Event}
Event := _
end
proc {WaitEvent Event}
{Wait @Event}
end
E = {NewEvent}
in
thread
{System.showInfo "[2] Waiting for event..."}
{WaitEvent E}
{System.showInfo "[2] Received event."}
end
{System.showInfo "[1] Waiting 1 second..."}
{Delay 1000}
{System.showInfo "[1] Signaling event."}
{SignalEvent E}</syntaxhighlight>
However, this code is quite unidiomatic. If we need to wait for an event just once (like in this example), we can simply use a dataflow variable, i.e. an event that cannot be reset:
<syntaxhighlight lang="oz">declare
E
in
thread
{System.showInfo "[2] Waiting for event..."}
{Wait E}
{System.showInfo "[2] Received event."}
end
{System.showInfo "[1] Waiting 1 second..."}
{Delay 1000}
{System.showInfo "[1] Signaling event."}
E = unit</syntaxhighlight>
If we want to synchronize two threads repeatedly and exchange data, it is natural to use ports and streams. Streams are just lists with an unbound tail. A port is basically a pointer to the tail of a list, i.e. it keeps track of where the next event can be written to:
<syntaxhighlight lang="oz">declare
MyPort
in
thread
MyStream
in
{NewPort ?MyStream ?MyPort}
{System.showInfo "[2] Waiting for event..."}
for Event in MyStream do
{System.showInfo "[2] Received event."}
{System.showInfo "[2] Waiting for event again..."}
end
end
for do
{System.showInfo "[1] Waiting 1 second..."}
{Delay 1000}
{System.showInfo "[1] Signaling event."}
{Port.send MyPort unit}
end</syntaxhighlight>
It is important to limit the scope of a stream as much as possible to ensure that the already read part of the stream is garbage-collected.
=={{header|Perl}}==
This is an example of using the [http://search.cpan.org/perldoc?AnyEvent AnyEvent] module.
The result is this: it prints "Hello world!" after one second, then after another second prints "Hi!" four times every quarter of a second and then immediately prints "Bye!" and quits:
<syntaxhighlight lang="perl">use AnyEvent;
# a new condition with a callback:
my $quit = AnyEvent->condvar(
cb => sub {
warn "Bye!\n";
}
);
# a new timer, starts after 2s and repeats every 0.25s:
my $counter = 1;
my $hi = AnyEvent->timer(
after => 2,
interval => 0.25,
cb => sub {
warn "Hi!\n";
# flag the condition as ready after 4 times:
$quit->send if ++$counter > 4;
}
);
# another timer, runs the callback once after 1s:
my $hello = AnyEvent->timer(
after => 1,
cb => sub {
warn "Hello world!\n";
}
);
# wait for the $quit condition to be ready:
$quit->recv();</syntaxhighlight>
This is the same using AnyEvent [http://search.cpan.org/perldoc?AE simplified API]:
<syntaxhighlight lang="perl">use AnyEvent;
my $quit = AE::cv sub { warn "Bye!\n" };
my $counter = 1;
my $hi = AE::timer 2, 0.25, sub {
warn "Hi!\n";
$quit->send if ++$counter > 4;
};
my $hello = AE::timer 1, 0, sub {
warn "Hello world!\n";
};
$quit->recv;</syntaxhighlight>
=={{header|Phix}}==
The primary synchronisation primitive in phix is the critical section, in the following the leave_cs()
in main() acts as signalling an event, and the one in echo() from whichever goes first acts to signal
that the other can/should resume.
<!--<syntaxhighlight lang="phix">(notonline)-->
<span style="color: #008080;">constant</span> <span style="color: #000000;">lock</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">init_cs</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">include</span> <span style="color: #000000;">timedate</span><span style="color: #0000FF;">.</span><span style="color: #000000;">e</span>
<span style="color: #008080;">procedure</span> <span style="color: #000000;">showtime</span><span style="color: #0000FF;">()</span>
<span style="color: #7060A8;">puts</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #000000;">format_timedate</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">date</span><span style="color: #0000FF;">(),</span><span style="color: #008000;">" h:m:s\n"</span><span style="color: #0000FF;">))</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">procedure</span>
<span style="color: #008080;">procedure</span> <span style="color: #000000;">echo</span><span style="color: #0000FF;">(</span><span style="color: #004080;">string</span> <span style="color: #000000;">s</span><span style="color: #0000FF;">)</span>
<span style="color: #7060A8;">sleep</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">rnd</span><span style="color: #0000FF;">()/</span><span style="color: #000000;">10</span><span style="color: #0000FF;">)</span> <span style="color: #000080;font-style:italic;">-- see note</span>
<span style="color: #7060A8;">enter_cs</span><span style="color: #0000FF;">(</span><span style="color: #000000;">lock</span><span style="color: #0000FF;">)</span>
<span style="color: #7060A8;">puts</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #000000;">s</span><span style="color: #0000FF;">)</span>
<span style="color: #7060A8;">sleep</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">showtime</span><span style="color: #0000FF;">()</span>
<span style="color: #7060A8;">leave_cs</span><span style="color: #0000FF;">(</span><span style="color: #000000;">lock</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">procedure</span>
<span style="color: #008080;">procedure</span> <span style="color: #000000;">main</span><span style="color: #0000FF;">()</span>
<span style="color: #7060A8;">enter_cs</span><span style="color: #0000FF;">(</span><span style="color: #000000;">lock</span><span style="color: #0000FF;">)</span>
<span style="color: #004080;">sequence</span> <span style="color: #000000;">threads</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">create_thread</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">routine_id</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"echo"</span><span style="color: #0000FF;">),{</span><span style="color: #008000;">"job1"</span><span style="color: #0000FF;">}),</span>
<span style="color: #000000;">create_thread</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">routine_id</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"echo"</span><span style="color: #0000FF;">),{</span><span style="color: #008000;">"job2"</span><span style="color: #0000FF;">})}</span>
<span style="color: #7060A8;">puts</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"main"</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">showtime</span><span style="color: #0000FF;">()</span>
<span style="color: #7060A8;">sleep</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">)</span>
<span style="color: #7060A8;">puts</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"free"</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">showtime</span><span style="color: #0000FF;">()</span>
<span style="color: #7060A8;">leave_cs</span><span style="color: #0000FF;">(</span><span style="color: #000000;">lock</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">wait_thread</span><span style="color: #0000FF;">(</span><span style="color: #000000;">threads</span><span style="color: #0000FF;">)</span>
<span style="color: #7060A8;">puts</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"done\n"</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">procedure</span>
<span style="color: #000000;">main</span><span style="color: #0000FF;">()</span>
<!--</syntaxhighlight>-->
{{out}}
Typically the first thread to attempt enter_cs() is released first, but there is
no guarantee of that. The sleep(rnd()/10) above evens out the likelihood, by
pausing for up to 0.1s, but otherwise isn't necessary.
<pre>
main 10:00:57
free 10:00:58
job2 10:00:59
job1 10:01:00
done
</pre>
External events such as timers and user input are handled in pGUI, eg
<!--<syntaxhighlight lang="phix">-->
<span style="color: #008080;">function</span> <span style="color: #000000;">timer_cb</span><span style="color: #0000FF;">(</span><span style="color: #004080;">Ihandle</span> <span style="color: #000080;font-style:italic;">/*ih*/</span><span style="color: #0000FF;">)</span>
<span style="color: #7060A8;">IupUpdate</span><span style="color: #0000FF;">(</span><span style="color: #000000;">canvas</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">return</span> <span style="color: #004600;">IUP_IGNORE</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
<span style="color: #004080;">Ihandle</span> <span style="color: #000000;">timer</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">IupTimer</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">Icallback</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"timer_cb"</span><span style="color: #0000FF;">),</span> <span style="color: #000000;">1000</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">function</span> <span style="color: #000000;">key_cb</span><span style="color: #0000FF;">(</span><span style="color: #004080;">Ihandle</span> <span style="color: #000080;font-style:italic;">/*ih*/</span><span style="color: #0000FF;">,</span> <span style="color: #004080;">atom</span> <span style="color: #000000;">c</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">c</span><span style="color: #0000FF;">=</span><span style="color: #004600;">K_ESC</span> <span style="color: #008080;">then</span> <span style="color: #008080;">return</span> <span style="color: #004600;">IUP_CLOSE</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">c</span><span style="color: #0000FF;">=</span><span style="color: #004600;">K_F5</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">iteration</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">0</span>
<span style="color: #7060A8;">IupSetInt</span><span style="color: #0000FF;">(</span><span style="color: #000000;">timer</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"RUN"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">1</span><span style="color: #0000FF;">)</span> <span style="color: #000080;font-style:italic;">-- (restart timer)</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">return</span> <span style="color: #004600;">IUP_CONTINUE</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
<span style="color: #7060A8;">IupSetCallback</span><span style="color: #0000FF;">(</span><span style="color: #000000;">dlg</span><span style="color: #0000FF;">,</span> <span style="color: #008000;">"K_ANY"</span><span style="color: #0000FF;">,</span> <span style="color: #7060A8;">Icallback</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"key_cb"</span><span style="color: #0000FF;">))</span>
<!--</syntaxhighlight>-->
=={{header|PicoLisp}}==
PicoLisp supports events from timers (via
'[http://software-lab.de/doc/refT.html#task task]' and
'[http://software-lab.de/doc/refA.html#alarm alarm]'),
file descriptors (also 'task') and various
'[http://software-lab.de/doc/refS.html#*Sig1 signals]'.
This will print a message after one second, then terminate the program after
another four seconds:
<syntaxhighlight lang="picolisp">(alarm 1
(prinl "Exit in 4 seconds")
(alarm 4 (bye)) )</syntaxhighlight>
=={{header|PowerShell}}==
<syntaxhighlight lang="powershell">
$timer = New-Object -TypeName System.Timers.Timer -Property @{Enabled=$true; Interval=1000; AutoReset=$true}
$action = {
$global:counter += 1
Write-Host “Event counter is ${counter}: $((Get-Date).ToString("hh:mm:ss"))”
if ($counter -ge $event.MessageData)
{
Write-Host “Timer stopped”
$timer.Stop()
}
}
$job = Register-ObjectEvent -InputObject $timer -MessageData 5 -SourceIdentifier Count -EventName Elapsed -Action $action
$global:counter = 0
& $job.Module {$global:counter}
</syntaxhighlight>
{{Out}}
<pre>
Event counter is 1: 04:58:04
Event counter is 2: 04:58:05
Event counter is 3: 04:58:06
Event counter is 4: 04:58:07
Event counter is 5: 04:58:08
Timer stopped
</pre>
=={{header|PureBasic}}==
<syntaxhighlight lang="purebasic">OpenWindow (0, 10, 10, 150, 40, "Event Demo")
ButtonGadget (1, 10, 10, 35, 20, "Quit")
Repeat
Event = WaitWindowEvent()
If Event = #PB_Event_Gadget And EventGadget() = 1
End
EndIf
ForEver</syntaxhighlight>
=={{header|Python}}==
<syntaxhighlight lang="python">
import threading
import time
def wait_for_event(event):
event.wait()
print("Thread: Got event")
e = threading.Event()
t = threading.Thread(target=wait_for_event, args=(e,))
t.start()
print("Main: Waiting one second")
time.sleep(1.0)
print("Main: Setting event")
e.set()
time.sleep(1.0)
print("Main: Done")
t.join()
</syntaxhighlight>
=={{header|Racket}}==
Racket comes with events as part of its implementation; various types of
events are used for different purposes: there are events that become
ready when some input is available in a port, when a TCP connection is
made, when a thread is dead, etc etc. Here we use a simple alarm event
as requested, even though it's a odd to send the actual event result to
the task (since it's a useless value):
<syntaxhighlight lang="racket">
#lang racket
(define task (thread (lambda () (printf "Got: ~s\n" (thread-receive)))))
(thread-send task ; wait for it, then send it
(sync (alarm-evt (+ 1000 (current-inexact-milliseconds)))))
(void (sync task)) ; wait for the task to be done before exiting
</syntaxhighlight>
=={{header|Raku}}==
(formerly Perl 6)
{{trans|Go}}
<syntaxhighlight lang="raku" line>note now, " program start";
my $event = Channel.new;
my $todo = start {
note now, " task start";
$event.receive;
note now, " event reset by task";
}
note now, " program sleeping";
sleep 1;
note now, " program signaling event";
$event.send(0);
await $todo;</syntaxhighlight>
{{out}}
<pre>Instant:1403880984.089974 program start
Instant:1403880984.095400 program sleeping
Instant:1403880984.095491 task start
Instant:1403880985.099381 program signaling event
Instant:1403880985.109395 event reset by task</pre>
See also [[Handle_a_signal#Raku]] for an example of using Supplies to do reactive programming based on events (Unix signals in this case).
=={{header|REXX}}==
Although REXX can be event driven, most events would probably have to be actively checked to see if the event occurs.
<br>Here is a ''time-driven'' example of events happening, based on specific timer ticks.
<syntaxhighlight lang="rexx">/*REXX program demonstrates a method of handling events (this is a time─driven pgm).*/
signal on halt /*allow user to HALT (Break) the pgm.*/
parse arg timeEvent /*allow the "event" to be specified. */
if timeEvent='' then timeEvent= 5 /*Not specified? Then use the default.*/
event?: do forever /*determine if an event has occurred. */
theEvent= right(time(), 1) /*maybe it's an event, ─or─ maybe not.*/
if pos(theEvent, timeEvent)>0 then signal happening
end /*forever*/
say 'Control should never get here!' /*This is a logic can─never─happen ! */
halt: say '════════════ program halted.'; exit 0 /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
happening: say 'an event occurred at' time()", the event is:" theEvent
do while theEvent==right(time(), 1) /*spin until a tic (a second) changes. */
nop /*replace NOP with the "process" code.*/
end /*while*/ /*NOP is a REXX statement, does nothing*/
signal event? /*see if another event has happened. */</syntaxhighlight>
{{out|output|text= when using the input of: <tt> 1 3 5 0 7 9 </tt>}}
<pre>
an event occurred at 16:13:29, the event is: 9
an event occurred at 16:13:30, the event is: 0
an event occurred at 16:13:31, the event is: 1
an event occurred at 16:13:33, the event is: 3
an event occurred at 16:13:35, the event is: 5
an event occurred at 16:13:37, the event is: 7
an event occurred at 16:13:39, the event is: 9
an event occurred at 16:13:40, the event is: 0
an event occurred at 16:13:41, the event is: 1
an event occurred at 16:13:43, the event is: 3
an event occurred at 16:13:45, the event is: 5
an event occurred at 16:13:47, the event is: 7
an event occurred at 16:13:49, the event is: 9
an event occurred at 16:13:50, the event is: 0
an event occurred at 16:13:51, the event is: 1
an event occurred at 16:13:53, the event is: 3
════════════ program halted.
</pre>
=={{header|Rust}}==
Rust ensures memory safety at compile-time without needing a garbage collector or runtime. There are several concurrency primitives in it's standard library.
<syntaxhighlight lang="rust">
use std::{sync::mpsc, thread, time::Duration};
fn main() -> Result<(), Box<dyn std::error::Error>> {
println!("[1] Starting");
let (tx, rx) = mpsc::channel();
thread::spawn(move || {
println!("[2] Waiting for event");
rx.recv();
println!("[2] Received event");
});
thread::sleep(Duration::from_secs(1));
println!("[1] Sending event");
tx.send(())?;
thread::sleep(Duration::from_secs(1));
Ok(())
}
</syntaxhighlight>
=={{header|Tcl}}==
Tcl has been event-driven since 7.5, but only supported channel and timer events (plus variable traces, which can be used to create event-like entitites). With the addition of coroutines, it becomes much simpler to create general events:
{{works with|Tcl|8.6}}
<
proc pause ms {
after $ms [info coroutine];yield
Line 140 ⟶ 1,258:
X signal
}
waitForTasksToFinish</
Output:
<pre>waiting for event
signalling X
received event</pre>
Of course, the classic way of writing this is much shorter, but intermingles the tasks:
<syntaxhighlight lang="tcl">after 1000 set X signalled
puts "waiting for event"
vwait X
puts "received event"</syntaxhighlight>
=={{header|Wren}}==
Wren-cli supports the scheduling of tasks using a timer.
The tasks to be executed are added to a list by the Scheduler class. The Timer.sleep method suspends the current fiber and signals the scheduler (by calling a private method) to execute the tasks one by one in their own fibers - in Wren only one fiber can execute at a time. The task results are then available to the main fiber on its resumption after Timer.sleep has completed.
<syntaxhighlight lang="wren">import "scheduler" for Scheduler
import "timer" for Timer
var a = 3
// add a task
Scheduler.add {
a = a * a
}
// add another task
Scheduler.add {
a = a + 1
}
System.print(a) // still 3
Timer.sleep(3000) // wait 3 seconds
System.print(a) // now 3 * 3 + 1 = 10</syntaxhighlight>
{{out}}
<pre>
3
10
</pre>
=={{header|Yabasic}}==
{{trans|Gambas}}
<syntaxhighlight lang="yabasic">
sub Timer1_Timer()
print Time$
end sub
</syntaxhighlight>
=={{header|zkl}}==
zkl provides an Atomics library for things like this. Events are async, waiting for an event doesn't poll.
<syntaxhighlight lang="zkl">var event=Atomic.Bool(); // False
// create thread waiting for event
fcn(event){event.wait(); println(vm," ping!")}.launch(event);
Atomic.sleep(1);
event.set();
println("done")</syntaxhighlight>
{{out}}
<pre>
// snooze
done // setting is fast, receiving maybe not so
VM#4 ping!
// and thread 4 exits
</pre>
I ran this from the REPL so I didn't have to worry about the main thread exiting and nuking the child thread.
{{omit from|GUISS}}
{{omit from|Maxima}}
{{omit from|PARI/GP}}
{{omit from|TI-83 BASIC}}
{{omit from|TI-89 BASIC}} <!-- Does not have concurrency or background processes. -->
| |||