Synchronous concurrency: Difference between revisions
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{{task|Concurrency}}{{requires|Concurrency}}{{omit from|BBC BASIC}}
The goal of this task is to create two concurrent activities ("[[Thread|Threads]]" or "Tasks", not [[Process|processes]].) that share data synchronously. Your language may provide syntax or libraries to perform concurrency. Different languages provide different implementations of concurrency, often with different names. Some languages use the term threads, others use the term tasks, while others use co-processes. This task should not be implemented using fork, spawn, or the [[Linux]]/[[UNIX]]/[[Windows|Win32]] pipe command, as communication should be between threads, not processes.
One of the concurrent units will read from a file named "input.txt" and send the contents of that file, one line at a time, to the other concurrent unit, which will print the line it receives to standard output. The printing unit must count the number of lines it prints. After the concurrent unit reading the file sends its last line to the printing unit, the reading unit will request the number of lines printed by the printing unit. The reading unit will then print the number of lines printed by the printing unit.
Line 7 ⟶ 8:
=={{header|Ada}}==
This Ada example starts by creating a package defining a single instance of a printing task. Ada requires packages to be separated into two parts. The package specification defines the interface to all public members of the package.
<
task Printer is
entry Put(Item : in String);
entry Get_Count(Count : out Natural);
end Printer;
end Synchronous_Concurrent;</
The package body contains the implementation of all the subprograms and tasks defined in the specification.
<
with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;
Line 39 ⟶ 40:
end Printer;
end Synchronous_Concurrent;</
Note that the task body contains an ''accept'' block for each ''entry'' defined in the task specification. When some other task calls an entry in the Printer task the communication between the tasks is synchronized.
Line 45 ⟶ 46:
The next file contains the ''main'' procedure for this program. The main or entry-point procedure for a program always runs in the ''environment'' task. For this program, the ''environment'' task is takes on the role of the file reading concurrent unit while the Printer task takes on the role of the printing concurrent unit.
<
with Ada.Text_Io; use Ada.Text_Io;
Line 63 ⟶ 64:
New_Line;
Put_Line("The task wrote" & Natural'Image(Num_Strings) & " strings.");
end Synchronous_Concurrent_Main;</
In this example only the environment task can call the entries on the Printer task. When the environment task completes the ''terminate'' option of the Printer task applies, terminating the Printer task. The environment task completes right after printing the number of lines sent through the Printer task. Because of the ''terminate'' option, the Printer task terminates just after the environment task prints the count.
=={{header|Aikido}}==
Aikido supports threads and monitors natively (built in to the language). There is also support for closures, but this example will use threads:
<syntaxhighlight lang="aikido">
monitor Queue {
var items = []
public function put (item) {
items.append (item)
notify()
}
public function get() {
while (items.size() == 0) {
wait()
}
var item = items[0]
items <<= 1
return item
}
public function close {
items.append (none)
}
}
thread reader (queue) {
var numlines = 0
for (;;) {
var line = queue.get()
if (typeof(line) == "none") {
break
}
print (line)
numlines++
}
println ("Number of lines: " + numlines)
}
thread writer (queue, lines) {
foreach line lines {
queue.put (line)
}
queue.close()
}
var queue = new Queue()
var lines = readfile ("input.txt")
var r = reader(queue)
var w = writer(queue, lines)
join (r)
join (w)</syntaxhighlight>
=={{header|ALGOL 68}}==
<
STRING line;
INT count := 0, errno;
BOOL input complete := FALSE;
SEMA output throttle = LEVEL 0, input throttle = LEVEL 1;
FILE input txt;
errno := open(input txt, "input.txt", stand in channel);
PROC call back done = (REF FILE f) BOOL: ( input complete := TRUE );
on logical file end(input txt, call back done);
PAR (
WHILE
Line 98 ⟶ 151:
);
print((count))
)</
=={{header|BCPL}}==
<syntaxhighlight lang="bcpl">// This is a BCPL implementation of the Rosettacode synchronous
// concurrency test using BCPL coroutines and a coroutine implementation
// of a Occum-style channels.
// BCPL is freely available from www.cl.cam.ac.uk/users/mr10
SECTION "coinout"
GET "libhdr.h"
GLOBAL {
tracing: ug
}
LET start() = VALOF
{ LET argv = VEC 50
LET in_co, out_co = 0, 0
LET channel = 0
LET filename = "input.txt"
UNLESS rdargs("-f,-t/S", argv, 50) DO
{ writef("Bad arguments for coinout*n")
RESULTIS 0
}
IF argv!0 DO filename := argv!0 // -f the source file
tracing := argv!1 // -t/S tracing option
in_co := initco(infn, 500, @channel)
out_co := initco(outfn, 500, @channel)
UNLESS in_co & out_co DO
{ writef("Trouble creating the coroutines*n")
GOTO fin
}
IF tracing DO writef("*nBoth in and out coroutines created*n*n")
callco(in_co, filename)
fin:
IF in_co DO deleteco(in_co)
IF out_co DO deleteco(out_co)
IF tracing DO writef("Both in and out coroutines deleted*n*n")
RESULTIS 0
}
AND readline(line) = VALOF
{ LET ch, i = 0, 0
line%0 := 0
{ ch := rdch()
IF ch=endstreamch RESULTIS FALSE
i := i+1
line%0, line%i := i, ch
IF ch='*n' | i=255 BREAK
} REPEAT
RESULTIS TRUE
}
AND infn(args) BE
{ LET channelptr = args!0
LET name = cowait() // Get the file name
LET instream = findinput(name)
LET line = VEC 256/bytesperword
UNLESS instream DO
{ writef("*nTrouble with file: %s*n", name)
RETURN
}
selectinput(instream)
{ LET ok = readline(line)
UNLESS ok BREAK
IF tracing DO
writef("inco: Sending a line to outco*n")
cowrite(channelptr, line)
} REPEAT
IF tracing DO
writef("inco: Sending zero to outco*n")
writef("*nNumber of lines written was %n*n", cowrite(channelptr, 0))
endstream(instream)
}
AND outfn(args) BE
{ LET channelptr = args!0
LET linecount = 0
{ LET line = coread(channelptr)
UNLESS line BREAK
IF tracing DO writef("outfn: Received a line*n")
writes(line)
linecount := linecount + 1
} REPEAT
IF tracing DO
writef("outfn: Received zero, so sent count=%n back to inco*n",
linecount)
cowait(linecount)
}
// The following functions are a implementation of Occum-style channels
// using coroutines.
// The first coroutine to request a transfer through a channel becomes
// suspended and the second causes the data to be transfers and then allows
// both coroutines to resume (in some order). The channel word is either
// zero or points to a suspended (read or write) cocoutine.
// The use of resumeco in coread is somewhat subtle!
AND coread(ptr) = VALOF
{ LET cptr = !ptr
TEST cptr
THEN { !ptr := 0 // Clear the channel word
RESULTIS resumeco(cptr, currco)
}
ELSE { !ptr := currco // Set channel word to this coroutine
RESULTIS cowait() // Wait for value from cowrite
}
}
AND cowrite(ptr, val) BE
{ LET cptr = !ptr
TEST cptr
THEN { !ptr := 0
callco(cptr, val) // Send val to coread
}
ELSE { !ptr := currco
callco(cowait(), val)
}
}
</syntaxhighlight>
=={{header|C}}==
{{libheader|libco}}
<syntaxhighlight lang="c">#include <stdlib.h> /* malloc(), realloc(), free() */
#include <stdio.h> /* fopen(), fgetc(), fwrite(), printf() */
#include <libco.h> /* co_create(), co_switch() */
void
fail(const char *message) {
perror(message);
exit(1);
}
/*
* These are global variables of this process. All cothreads of this
* process will share these global variables.
*/
cothread_t reader;
cothread_t printer;
struct {
char *buf; /* Not a C string. No terminating '\0'. */
size_t len; /* Length of line in buffer. */
size_t cap; /* Maximum capacity of buffer. */
} line;
size_t count; /* Number of lines printed. */
/*
* The reader cothread reads every line of an input file, passes each
* line to the printer cothread, and reports the number of lines.
*/
void
reader_entry(void)
{
FILE *input;
size_t newcap;
int c, eof, eol;
char *newbuf;
input = fopen("input.txt", "r");
if (input == NULL)
fail("fopen");
line.buf = malloc(line.cap = 4096); /* New buffer. */
if (line.buf == NULL)
fail("malloc");
line.len = 0; /* Start with an empty line. */
do {
c = fgetc(input); /* Read next character. */
if (ferror(input))
fail("fgetc");
eof = (c == EOF);
if (eof) {
/*
* End of file is also end of line,
` * unless the line would be empty.
*/
eol = (line.len > 0);
} else {
/* Append c to the buffer. */
if (line.len == line.cap) {
/* Need a bigger buffer! */
newcap = line.cap * 2;
newbuf = realloc(line.buf, newcap);
if (newbuf == NULL)
fail("realloc");
line.buf = newbuf;
line.cap = newcap;
}
line.buf[line.len++] = c;
/* '\n' is end of line. */
eol = (c == '\n');
}
if (eol) {
/* Pass our complete line to the printer. */
co_switch(printer);
line.len = 0; /* Destroy our line. */
}
} while (!eof);
free(line.buf);
line.buf = NULL; /* Stops a loop in the printer. */
printf("Printed %zu lines.\n", count);
co_switch(printer);
}
/*
* The printer cothread starts the reader cothread, prints every line
* line from the reader cothread, and counts the number of lines.
*/
int
main()
{
reader = co_create(4096, reader_entry);
printer = co_active();
count = 0;
for (;;) {
co_switch(reader);
if (line.buf == NULL)
break;
/* Print this line. Count it. */
fwrite(line.buf, 1, line.len, stdout);
count++;
}
co_delete(reader);
return 0;
}</syntaxhighlight>
=={{header|C sharp}}==
<syntaxhighlight lang="csharp">using System;
using System.Threading.Tasks;
using System.Collections.Concurrent;
using System.IO;
namespace SynchronousConcurrency
{
class Program
{
static void Main(string[] args)
{
BlockingCollection<string> toWriterTask = new BlockingCollection<string>();
BlockingCollection<int> fromWriterTask = new BlockingCollection<int>();
Task writer = Task.Factory.StartNew(() => ConsoleWriter(toWriterTask, fromWriterTask));
Task reader = Task.Factory.StartNew(() => FileReader(fromWriterTask, toWriterTask));
Task.WaitAll(writer, reader);
}
static void ConsoleWriter(BlockingCollection<string> input, BlockingCollection<int> output)
{
int nLines = 0;
string line;
while ((line = input.Take()) != null)
{
Console.WriteLine(line);
++nLines;
}
output.Add(nLines);
}
static void FileReader(BlockingCollection<int> input, BlockingCollection<string> output)
{
StreamReader file = new StreamReader("input.txt"); // TODO: check exceptions
string line;
while ((line = file.ReadLine()) != null)
{
output.Add(line);
}
output.Add(null); // EOF
Console.WriteLine("line count: " + input.Take());
}
}
}</syntaxhighlight>
{{out}}
<pre>
foo
bar
baz
xenu 666
line count: 4
</pre>
=={{header|C++}}==
{{works with|C++11}}
<syntaxhighlight lang="cpp">#include <future>
#include <iostream>
#include <fstream>
#include <mutex>
#include <queue>
#include <string>
#include <thread>
struct lock_queue
{
std::queue<std::string> q;
std::mutex mutex;
};
void reader(std::string filename, std::future<size_t> lines, lock_queue& out)
{
std::string line;
std::ifstream in(filename);
while(std::getline(in, line)) {
line += '\n';
std::lock_guard<std::mutex> lock(out.mutex);
out.q.push(line);
} {
std::lock_guard<std::mutex> lock(out.mutex);
out.q.push("");
}
lines.wait();
std::cout << "\nPrinted " << lines.get() << " lines\n";
}
void printer(std::promise<size_t> lines, lock_queue& in)
{
std::string s;
size_t line_n = 0;
bool print = false;
while(true) {
{
std::lock_guard<std::mutex> lock(in.mutex);
if(( print = not in.q.empty() )) { //Assignment intended
s = in.q.front();
in.q.pop();
}
}
if(print) {
if(s == "") break;
std::cout << s;
++line_n;
print = false;
}
}
lines.set_value(line_n);
}
int main()
{
lock_queue queue;
std::promise<size_t> promise;
std::thread t1(reader, "input.txt", promise.get_future(), std::ref(queue));
std::thread t2(printer, std::move(promise), std::ref(queue));
t1.join(); t2.join();
}</syntaxhighlight>
{{out}}
<pre>
Lorem ipsum dolor sit amet, consectetur adipisicing elit,
sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam,
quis nostrud exercitation ullamco laboris
nisi ut aliquip ex ea commodo consequat.
Duis aute irure dolor in reprehenderit in voluptate velit
esse cillum dolore eu fugiat nulla pariatur.
Excepteur sint occaecat cupidatat non proident,
sunt in culpa qui officia deserunt mollit anim id est laborum.
Printed 9 lines
</pre>
=={{header|Clojure}}==
Line 105 ⟶ 545:
The ''state'' argument is the agent's state at the start of the call, and the last expression becomes the agent's new state.
<syntaxhighlight lang="clojure">(use '[clojure.java.io :as io])
(def writer (agent 0))
Line 111 ⟶ 551:
(defn write-line [state line]
(println line)
(inc state))</
The reader executes on the main thread. It passes each line to the writer -- the ''send'' call returns immediately, waits until the writer has finished writing all the lines, gets the line count & prints it, and terminates the writer.
<syntaxhighlight lang
(
(send writer write-line line)))
(await writer)
(println "lines written:" @writer)
(shutdown-agents)</
That's it!
Line 128 ⟶ 569:
First, implement message-passing:
<
(defclass queue ()
Line 186 ⟶ 627:
`(receive-message (,message . ,body)))
(defun queue () (make-instance 'queue))</
Should be easy from now on:
<
(with-open-file (stream pathname)
(loop for line = (read-line stream nil)
Line 222 ⟶ 663:
(thread reader (reader pathname writer))
(thread writer (writer *standard-output* reader)))
(values))</
And now an example:
<
foo
bar
Line 232 ⟶ 673:
xenu 666
line count: 4
; No value</
Note that to run the example from the SLIME REPL you need to put:
Line 239 ⟶ 680:
in your <code>~/.swank.lisp</code>
=={{header|Crystal}}==
<syntaxhighlight lang="ruby">File.write("input.txt", "a\nb\nc")
lines = Channel(String).new
spawn do
File.each_line("input.txt") do |line|
lines.send(line)
end
lines.close
end
while line = lines.receive?
puts line
end
File.delete("input.txt")</syntaxhighlight>
<pre>
a
b
c
</pre>
=={{header|D}}==
<syntaxhighlight lang="d">import std.algorithm, std.concurrency, std.stdio;
void main() {
auto printer = spawn(&printTask, thisTid);
auto f = File("input.txt","r");
foreach (string
send(printer, line);
send(printer, true); //EOF
auto n = receiveOnly!(int)();
stdout.writefln("\n%d lines printed.", n);
}
void printTask(Tid reader) {
int
(bool) {send(reader, n); eof = true;}
}
</syntaxhighlight>
=={{header|Delphi}}==
<syntaxhighlight lang="delphi">
program Project2;
{$APPTYPE CONSOLE}
uses
SysUtils, Classes, Windows;
type
EThreadStackFinalized = class(Exception);
PLine = ^TLine;
TLine = record
Text: string;
end;
TThreadQueue = class
private
FFinalized: Boolean;
FQueue: THandle;
public
constructor Create;
destructor Destroy; override;
procedure Finalize;
procedure Push(Data: Pointer);
function Pop(var Data: Pointer): Boolean;
property Finalized: Boolean read FFinalized;
end;
TPrintThread = class(TThread)
private
FCount: Integer;
FTreminateEvent: THandle;
FDoneEvent: THandle;
FQueue: TThreadQueue;
public
constructor Create(aTreminateEvent, aDoneEvent: THandle; aQueue: TThreadQueue);
procedure Execute; override;
property Count: Integer read FCount;
end;
{ TThreadQueue }
constructor TThreadQueue.Create;
begin
FQueue := CreateIOCompletionPort(INVALID_HANDLE_VALUE, 0, 0, 0);
FFinalized := False;
end;
destructor TThreadQueue.Destroy;
begin
if FQueue <> 0 then
CloseHandle(FQueue);
inherited;
end;
procedure TThreadQueue.Finalize;
begin
PostQueuedCompletionStatus(FQueue, 0, 0, Pointer($FFFFFFFF));
FFinalized := True;
end;
function TThreadQueue.Pop(var Data: Pointer): Boolean;
var
A: Cardinal;
OL: POverLapped;
begin
Result := True;
if not FFinalized then
GetQueuedCompletionStatus(FQueue, A, Cardinal(Data), OL, INFINITE);
if FFinalized or (OL = Pointer($FFFFFFFF)) then begin
Data := nil;
Result := False;
Finalize;
end;
end;
procedure TThreadQueue.Push(Data: Pointer);
begin
if FFinalized then
raise EThreadStackFinalized.Create('Stack is finalized');
PostQueuedCompletionStatus(FQueue, 0, Cardinal(Data), nil);
end;
{ TPrintThread }
constructor TPrintThread.Create(aTreminateEvent, aDoneEvent: THandle; aQueue: TThreadQueue);
begin
inherited Create(True);
FCount := 0;
FreeOnTerminate := True;
FTreminateEvent := aTreminateEvent;
FDoneEvent := aDoneEvent;
FQueue := aQueue;
end;
procedure TPrintThread.Execute;
var
data: Pointer;
line: PLine;
begin
repeat
if FQueue.Pop(data) then begin
line := data;
try
Writeln(line^.Text);
if line^.Text = #0 then
SetEvent(FDoneEvent);
Inc(FCount);
finally
Dispose(line);
end;
end;
until False;
WaitForSingleObject(FTreminateEvent, INFINITE);
end;
var
PrintThread: TPrintThread;
Queue: TThreadQueue;
lines: TStrings;
i: Integer;
line: PLine;
TreminateEvent, DoneEvent: THandle;
begin
Queue := TThreadQueue.Create;
try
TreminateEvent := CreateEvent(nil, False, False, 'TERMINATE_EVENT');
DoneEvent := CreateEvent(nil, False, False, 'DONE_EVENT');
try
PrintThread := TPrintThread.Create(TreminateEvent, DoneEvent, Queue);
PrintThread.Start;
lines := TStringList.Create;
try
lines.LoadFromFile('input.txt');
for i := 0 to lines.Count - 1 do begin
New(line);
line^.Text := lines[i];
Queue.Push(line);
end;
New(line);
line^.Text := #0;
Queue.Push(line);
WaitForSingleObject(DoneEvent, INFINITE);
New(line);
line^.Text := IntToStr(PrintThread.Count);
Queue.Push(line);
SetEvent(TreminateEvent);
finally
lines.Free;
end;
finally
CloseHandle(TreminateEvent);
CloseHandle(DoneEvent)
end;
Readln;
finally
Queue.Free;
end;
end.
</syntaxhighlight>
=={{header|E}}==
<
var count := 0
def printer {
Line 305 ⟶ 931:
# Stream IO in E is not finished yet, so this example just uses a list.
sender(<file:input.txt>.getText().split("\n"))</
=={{header|EchoLisp}}==
This task uses two processes, reader/writer, synchronized by a semaphore S and its queue of messages. The reader sends write or reader-count-please messages. The writer responds with ack or count messages.
<syntaxhighlight lang="scheme">
(require 'sequences)
(require 'tasks)
;; inter-tasks message : (op-code . data)
(define (is-message? op message)
(and message (equal? op (first message))))
;; reader task
(define (reader infile )
(wait S)
(define message (semaphore-pop S))
(when (is-message? 'count message ) (writeln 'reader-> message) (task-stop-all))
(if (first infile) ;; not EOF
(set! message (cons 'write (next infile)))
(set! message (list 'reader-count-please)))
(semaphore-push S message)
(signal S)
infile)
(define (writer count)
(wait S)
(define message (semaphore-pop S))
(when (is-message? 'write message )
(writeln (rest message))
(set! count (1+ count))
(set! message (cons 'ack count)))
(when (is-message? 'reader-count-please message )
(set! message (cons 'count count)))
(semaphore-push S message)
(signal S)
count)
</syntaxhighlight>
{{out}}
<pre>
;; input sequence
(define infile null) ;; input file handle
(define (set-infile name text) (set! infile (procrastinator (string-split text "\n"))))
(file->string set-infile "input.txt")
(define S (make-semaphore 1)) ;; semaphore to synchronize
(task-run (make-task reader infile))
(task-run (make-task writer 0))
#task:id:165:running
#task:id:166:running
Well, it's one for the money
Two for the show
Three to get ready
Now go, cat, go
But don't you
Step on my blue suede shoes
You can do anything
But stay off of my blue suede shoes
Well, you can knock me down
[lines skipped ...]
Blue, suede shoes, baby
Blue, blue
Blue suede shoes
Well, you can do anything
But stay off of my blue suede shoes!
reader-> (count . 53)
</pre>
=={{header|Elixir}}==
{{trans|Erlang}}
<syntaxhighlight lang="elixir">defmodule RC do
def start do
my_pid = self
pid = spawn( fn -> reader(my_pid, 0) end )
File.open( "input.txt", [:read], fn io ->
process( IO.gets(io, ""), io, pid )
end )
end
defp process( :eof, _io, pid ) do
send( pid, :count )
receive do
i -> IO.puts "Count:#{i}"
end
end
defp process( any, io, pid ) do
send( pid, any )
process( IO.gets(io, ""), io, pid )
end
defp reader( pid, c ) do
receive do
:count -> send( pid, c )
any ->
IO.write any
reader( pid, c+1 )
end
end
end
RC.start</syntaxhighlight>
=={{header|Erlang}}==
<
-export([start/0]).
start() ->
Pid = erlang:spawn( fun() -> reader(My_pid, 0) end ),
process( io:get_line(IO, ""), IO, Pid ),
file:close( IO ).
process( eof, _IO, Pid ) ->
Pid ! count,
receive
I -> io:fwrite("Count:~p~n", [I])
end
process( Any, IO, Pid ) ->
Pid ! Any,
process( io:get_line(IO, ""), IO, Pid ).
reader(Pid, C) ->
Line 343 ⟶ 1,066:
io:fwrite("~s", [Any]),
reader(Pid, C+1)
end.</
=={{header|Euphoria}}==
<syntaxhighlight lang="euphoria">sequence lines
sequence count
lines = {}
count = {}
procedure read(integer fn)
object line
while 1 do
line = gets(fn)
if atom(line) then
exit
else
lines = append(lines, line)
task_yield()
end if
end while
lines = append(lines,0)
while length(count) = 0 do
task_yield()
end while
printf(1,"Count: %d\n",count[1])
end procedure
procedure write(integer fn)
integer n
object line
n = 0
while 1 do
while length(lines) = 0 do
task_yield()
end while
line = lines[1]
lines = lines[2..$]
if atom(line) then
exit
else
puts(fn,line)
n += 1
end if
end while
count = append(count,n)
end procedure
integer fn
atom reader, writer
constant stdout = 1
fn = open("input.txt","r")
reader = task_create(routine_id("read"),{fn})
writer = task_create(routine_id("write"),{stdout})
task_schedule(writer,1)
task_schedule(reader,1)
while length(task_list()) > 1 do
task_yield()
end while</syntaxhighlight>
=={{header|F_Sharp|F#}}==
This code will read lines from the file on one thread, and print them to the console on one or more other
threads from the ThreadPool, using a MailboxProcessor for lock-free communication between threads and tracking the line count without the use of mutable state.
<syntaxhighlight lang="fsharp">
open System.IO
type Msg =
| PrintLine of string
| GetCount of AsyncReplyChannel<int>
let printer =
MailboxProcessor.Start(fun inbox ->
let rec loop count =
async {
let! msg = inbox.Receive()
match msg with
| PrintLine(s) ->
printfn "%s" s
return! loop (count + 1)
| GetCount(reply) ->
reply.Reply(count)
return! loop count
}
loop 0
)
let reader (printAgent:MailboxProcessor<Msg>) file =
File.ReadLines(file)
|> Seq.iter (fun line -> PrintLine line |> printAgent.Post)
printAgent.PostAndReply(fun reply -> GetCount(reply))
|> printfn "Lines written: %i"
reader printer @"c:\temp\input.txt"
</syntaxhighlight>
=={{header|Forth}}==
Tested in GForth 0.7.3. First, 'co.fs' - the coroutines library, then the output of the application on himself,
result of the command-line: 'cat synco.fs | gforth synco.fs'.
<syntaxhighlight lang="forth">\
\ co.fs Coroutines by continuations.
\
\ * Circular Queue. Capacity is power of 2.
\
VARIABLE HEAD VARIABLE TAIL
128 CELLS CONSTANT CQ#
\ * align by queue capacity
HERE DUP
CQ# 1- INVERT AND CQ# +
SWAP - ALLOT
\
HERE CQ# ALLOT CONSTANT START
\
: ADJUST ( -- ) [ CQ# 1- ]L AND START + ;
: PUT ( n-- ) TAIL @ TUCK ! CELL+ ADJUST TAIL ! ;
: TAKE ( --n ) HEAD @ DUP @ SWAP CELL+ ADJUST HEAD ! ;
: 0CQ ( -- ) START DUP HEAD ! TAIL ! ; 0CQ
: NOEMPTY? ( --f ) HEAD @ TAIL @ <> ;
: ;CO ( -- ) TAKE >R ;
\
\ * COROUTINES LEXEME
\
: CO: ( -- ) R> PUT ; \ Register continuation as coroutine. Exit.
: CO ( -- ) R> PUT TAKE >R ; \ Co-route.
: GO ( -- ) BEGIN NOEMPTY? WHILE ;CO REPEAT ; \ :-)
\
\ * CHANNELS LEXEME
\
: CHAN? ( a--f ) 2@ XOR ;
</syntaxhighlight>
{{out}}
<pre>
\ synco.fs Synchronous concurrency for RosettaCode
include co.fs
: STRING@ DUP CELL + SWAP @ ;
2VARIABLE CHAN
\
\ * READER LEXEME
\
4096 CONSTANT L#
CREATE Line 0 , L# ALLOT
: READER
CO:
BEGIN
Line cell+ L# STDIN read-line THROW
WHILE
Line !
0 Line CHAN 2!
CO
REPEAT DROP
Line DUP CHAN 2!
\ -- Wait for report back
BEGIN CO CHAN CHAN? UNTIL
\ -- Have it, show and go
CR S" -------" TYPE
CR S" LINES: " TYPE CHAN @ ?
;
\
\ * WRITER LEXEME
\
VARIABLE X
: WRITER
CO:
BEGIN
CHAN CHAN?
WHILE
CHAN @ STRING@ TYPE CR
1 X +!
CO
REPEAT
\ -- Chance to stop other writers
CO
\ -- First of writers reports back
\ -- the shared global counter
CHAN CHAN? 0=
IF
0 X CHAN 2!
CO
THEN
;
\
\ * RUNNER
\
0 X ! READER WRITER ( WRITER WRITER :-) GO CR BYE
-------
LINES: 59
</pre>
=={{header|Go}}==
<syntaxhighlight lang="go">package main
import (
"bufio"
"fmt"
"log"
"os"
)
func main() {
lines := make(chan string)
count := make(chan int)
go func() {
c := 0
for l := range lines {
fmt.Println(l)
c++
}
count <- c
}()
f, err := os.Open("input.txt")
if err != nil {
log.Fatal(err)
}
for s := bufio.NewScanner(f); s.Scan(); {
lines <- s.Text()
}
f.Close()
close(lines)
fmt.Println("Number of lines:", <-count)
}</syntaxhighlight>
=={{header|Haskell}}==
Line 359 ⟶ 1,313:
The code below defines various signals in terms of takeMVar and putMVar and then passes those to the parts of the code which should be permitted to use them. Note that this way, it is impossible for the reader process to take the current line, for example.
<
import Control.Concurrent.MVar
Line 373 ⟶ 1,327:
forkIO $ writer takeLine putCount
reader putLine putEOF takeCount</
The reader simply reads the file lazily, applying putLine to each of the lines in turn, which blocks until the writer has taken the line. It then signals that it is finished with putEOF, and then takes the count and prints it.
<
do ls <- fmap lines (readFile "input.txt")
mapM putLine ls
putEOF
n <- takeCount
print n</
The writer gets the lines in a loop with takeLine until it receives Nothing, at which point it uses putCount to tell the reader how many lines there were.
<
where loop n = do l <- takeLine
case l of
Just x -> do putStrLn x
loop (n+1)
Nothing -> putCount n</
=={{header|Icon}} and {{header|Unicon}}==
Icon does not support concurrent programming. Co-expressions can be used in
Icon to mimic some of the behavior, but they are not truly concurrently
executed.
Unicon supports concurrent programming. A Unicon solution is:
<syntaxhighlight lang="unicon">procedure main(A)
fName := A[1]|"index.txt"
p := thread produce(fName)
c := thread consume(p)
every wait(p | c)
end
procedure
every !open(fName)@>> # drop messages in p's outbox (blocking whenever box is full)
@>> # Signal consumer that p is done
write("count is ",<<@) # block until message in p's inbox
end
procedure
while write(\<<@p) do (i+:=1) # loop until empty message in p's outbox
# (blocking until each message arrives)
i@>>p # put row count into p's inbox
end</syntaxhighlight>
Sample output:
<pre>
->pc
procedure main()
n := 5134
x := *n
write(x)
end
count is 5
->
</pre>
=={{header|J}}==
Implementation:
<syntaxhighlight lang="j">input=: 1 :0
nlines=: 0
u;._2@fread 'input.txt'
smoutput nlines
)
output=: 3 :0
nlines=: nlines+1
smoutput y
)</syntaxhighlight>
Usage:
<syntaxhighlight lang="j"> output input</syntaxhighlight>
Note that we are not using OS threads here, but instead - as specified by this task - are using two concurrent activities which share data synchronously.
=={{header|Java}}==
<syntaxhighlight lang="java">import java.io.BufferedReader;
import java.io.FileReader;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
class SynchronousConcurrency
{
public static void main(String[] args) throws Exception
{
final AtomicLong lineCount = new AtomicLong(0);
final BlockingQueue<String> queue = new LinkedBlockingQueue<String>();
final String EOF = new String();
final Thread writerThread = new Thread(new Runnable() {
public void run()
{
long linesWrote = 0;
while (true)
{
try
{
String line = queue.take();
// Reference equality
if (line == EOF)
break;
System.out.println(line);
linesWrote++;
}
catch (InterruptedException ie)
{ }
}
lineCount.set(linesWrote);
}
}
);
writerThread.start();
// No need to start a third thread for the reader, just use this thread
BufferedReader br = new BufferedReader(new FileReader("input.txt"));
String line;
while ((line = br.readLine()) != null)
queue.put(line);
br.close();
queue.put(EOF);
writerThread.join();
// AtomicLong is not needed here due to memory barrier created by thread join, but still need a mutable long since lineCount must be final to access it from an anonymous class
System.out.println("Line count: " + lineCount.get());
return;
}
}
</syntaxhighlight>
=={{header|Julia}}==
<syntaxhighlight lang="julia">
function inputlines(txtfile, iochannel)
for line in readlines(txtfile)
Base.put!(iochannel, line)
end
Base.put!(iochannel, nothing)
println("The other task printed $(take!(iochannel)) lines.")
end
function outputlines(iochannel)
totallines = 0
while (line = Base.take!(iochannel)) != nothing
totallines += 1
println(line)
end
Base.put!(iochannel, totallines)
end
c = Channel(0)
@async inputlines("filename.txt", c)
outputlines(c)
</syntaxhighlight>
=={{header|Kotlin}}==
===Using threads===
<syntaxhighlight lang="kotlin">import java.util.concurrent.SynchronousQueue
import kotlin.concurrent.thread
import java.io.File
const val EOT = "\u0004" // end of transmission
fun main(args: Array<String>) {
val queue = SynchronousQueue<String>()
val work = thread {
var count = 0
while (true) {
val line = queue.take()
if (line == EOT) {
queue.put(count.toString())
break
}
println(line)
count++
}
}
File("input.txt").forEachLine { line -> queue.put(line) }
queue.put(EOT)
work.join()
val count = queue.take().toInt()
println("\nNumber of lines printed = $count")
}</syntaxhighlight>
Content of input.txt:
<pre>
line1
line2
line3
line4
</pre>
{{out}}
<pre>
line1
line2
line3
line4
Number of lines printed = 4
</pre>
===Using coroutines===
Uses experimental features and will change in the future. Same output as the threads version.
<syntaxhighlight lang="kotlin">// version 1.3.20 with kotlinx-coroutines-core version 1.1.1
import kotlinx.coroutines.async
import kotlinx.coroutines.channels.Channel
import kotlinx.coroutines.channels.sumBy
import kotlinx.coroutines.coroutineScope
import java.io.File
suspend fun main() {
coroutineScope {
val lines = Channel<String>()
val count = async {
lines.sumBy { line ->
println(line)
1
}
}
File("input.txt").bufferedReader().forEachLine { line -> lines.send(line) }
println("\nNumber of lines printed = ${count.await()}")
}
}</syntaxhighlight>
=={{header|Logtalk}}==
The following example can be found in the Logtalk distribution and is used here with permission. The "input.txt" file contains the terms "a(0)..a(9)", one per line. Works when using SWI-Prolog, XSB, or YAP as the backend compiler.
<syntaxhighlight lang="logtalk">
:- object(team).
:- threaded.
:- public(start/0).
start :-
threaded((
reader,
writer(0)
)).
reader :-
open('input.txt', read, Stream),
repeat,
read_term(Stream, Term, []),
threaded_notify(term(Term)),
Term == end_of_file,
!,
close(Stream),
threaded_wait(lines(Lines)),
write('Number of lines: '), write(Lines), nl.
writer(N0) :-
threaded_wait(term(Term)),
( Term == end_of_file ->
threaded_notify(lines(N0))
; N is N0 + 1,
write(Term), nl,
writer(N)
).
:- end_object.
</syntaxhighlight>
Output:
<syntaxhighlight lang="text">
| ?- ?- team::start.
a(0)
a(1)
a(2)
a(3)
a(4)
a(5)
a(6)
a(7)
a(8)
a(9)
Number of lines: 10
true.
</syntaxhighlight>
=={{header|Lua}}==
<syntaxhighlight lang="lua">function ReadFile()
local fp = io.open( "input.txt" )
assert( fp ~= nil )
for line in fp:lines() do
coroutine.yield( line )
end
fp:close()
end
co = coroutine.create( ReadFile )
while true do
local status, val = coroutine.resume( co )
if coroutine.status( co ) == "dead" then break end
print( val )
end
</syntaxhighlight>
=={{header|Mercury}}==
<syntaxhighlight lang="mercury">:- module synchronous_concurrency.
:- interface.
:- import_module io.
:- pred main(io::di, io::uo) is cc_multi.
:- implementation.
:- import_module int, list, string, thread, thread.channel, thread.mvar.
:- type line_or_stop
---> line(string)
; stop.
main(!IO) :-
io.open_input("input.txt", Res, !IO),
(
Res = ok(Input),
channel.init(Channel, !IO),
mvar.init(MVar, !IO),
thread.spawn(writer(Channel, MVar, 0), !IO),
reader(Input, Channel, MVar, !IO)
;
Res = error(Err),
io.format("Error opening file: %s\n", [s(io.error_message(Err))], !IO)
).
:- pred reader(io.text_input_stream::in, channel(line_or_stop)::in, mvar(int)::in,
io::di, io::uo) is det.
reader(Input, Channel, MVar, !IO) :-
io.read_line_as_string(Input, Res, !IO),
(
Res = ok(Line),
channel.put(Channel, line(Line), !IO),
reader(Input, Channel, MVar, !IO)
;
Res = eof,
channel.put(Channel, stop, !IO),
mvar.take(MVar, Count, !IO),
io.format("%d lines printed.\n", [i(Count)], !IO)
;
Res = error(Err),
channel.put(Channel, stop, !IO),
io.format("Error reading file: %s\n", [s(io.error_message(Err))], !IO)
).
:- pred writer(channel(line_or_stop)::in, mvar(int)::in, int::in,
io::di, io::uo) is cc_multi.
writer(Channel, MVar, Count, !IO) :-
channel.take(Channel, LineOrStop, !IO),
(
LineOrStop = line(Line),
io.write_string(Line, !IO),
writer(Channel, MVar, Count + 1, !IO)
;
LineOrStop = stop,
mvar.put(MVar, Count, !IO)
).</syntaxhighlight>
=={{header|Nim}}==
Compile with <code>nim --threads:on c sync.nim</code>:
{{trans|Python}}
Two threads are spun up that communicate over a channel.
<syntaxhighlight lang="nim">var msgs: Channel[string]
var count: Channel[int]
const FILE = "input.txt"
proc read() {.thread.} =
for line in FILE.lines:
msgs.send(line)
msgs.send("")
echo count.recv()
count.close()
proc print() {.thread.} =
var n = 0
while true:
var msg = msgs.recv()
if msg.len == 0:
break
echo msg
n += 1
msgs.close()
count.send(n)
var reader_thread = Thread[void]()
var printer_thread = Thread[void]()
msgs.open()
count.open()
createThread(reader_thread, read)
createThread(printer_thread, print)
joinThreads(reader_thread, printer_thread)</syntaxhighlight>
=={{header|OCaml}}==
===Using only the standard library===
We use the built-in Event module to provide communication channels between threads.
<syntaxhighlight lang
The reader is a simple loop. It starts by opening a file, then reads lines from that file until there is nothing left to read. After each line, it sends <tt>Some v</tt> on channel <tt>lines_dest</tt>, where <tt>v</tt> is the contents of the line. Once there are no lines anymore,
exception <tt>End_of_file</tt> is raised and we send <tt>None</tt> on that same channel. After that, it's just the matter of waiting for one message on <tt>count_source</tt>, closing the file and printing the result:
<syntaxhighlight lang
let file = open_in "input.txt" in
let rec aux () =
let line = try Some (input_line file)
with End_of_file -> None in
sync (send
match line with
| Some _ -> aux ()
Line 442 ⟶ 1,759:
Printf.printf "The task wrote %i strings\n" printed;
close_in file
in aux ()</
The printer is also a simple loop. It keeps receiving messages on <tt>lines_source</tt>. If a message has structure <tt>Some v</tt>, then <tt>v</tt> is a line, print it and increment the counter. Otherwise, the message has structure <tt>None</tt>, which means that we're done, just send the number of lines on <tt>count_dest</tt>:
<
let rec aux i =
match sync (receive lines_source) with
| Some line -> print_endline line; aux ( i + 1 )
| None -> sync (send count_target i)
in aux 0</
Finally, our main program creates both communication channels and backgrounds treatment of <tt>printer</tt>:
<
let count = new_channel ()
and lines = new_channel ()
in
let _ = Thread.create (printer lines) count
in reader count lines</
Note that, had we decided to background treatment of <tt>reader</tt> instead, an additional synchronization would have been necessary to prevent the program from leaving once the main thread is over.
=={{header|Oforth}}==
Oforth implements concurrency with tasks and communication between tasks using channels. Here, we create 2 channels (one for print, one to retrieve the number of lines).
When the file has been read and sent to channel chPrint, this channel is closed. All tasks waiting for an object in this channel are released and receive null. Then printing task returns number of printed lines into chCount channel for the main task.
<syntaxhighlight lang="oforth">import: parallel
: printing(chPrint, chCount)
0 while( chPrint receive dup notNull ) [ println 1+ ] drop
chCount send drop ;
: concurrentPrint(aFileName)
| chPrint chCount line |
Channel new ->chPrint
Channel new ->chCount
#[ printing(chPrint, chCount) ] &
aFileName File new forEach: line [ chPrint send(line) drop ]
chPrint close
chCount receive "Number of lines printed : " print println ;</syntaxhighlight>
=={{header|Ol}}==
We use lazy file reading to not a load full file content into memory.
Additionally, we send just a "#true" into coroutines as a message placeholder because we do not analyze (in this sample) a message content.
Source code:
<syntaxhighlight lang="scheme">
(import (owl parse))
(coroutine 'reader (lambda ()
; lazy line-by-line file reader
(define (not-a-newline x) (not (eq? x #\newline)))
(define parser (let-parse*
((line (greedy* (byte-if not-a-newline)))
(newline (imm #\newline)))
(bytes->string line)))
(define file (file->bytestream "input.txt"))
(let loop ((in (try-parse parser file #false)))
(cond
((not in) ; file is ended
(define envelope (wait-mail)) ; wait for a request
(mail (ref envelope 1) #eof)) ; send an end-of-file to caller
((pair? in) ; new line is read
(define envelope (wait-mail)) ; wait for a request
(mail (ref envelope 1) (car in)) ; send a line to caller
(loop (try-parse parser (cdr in) #false)))
(else ; just a lazy read, let's repeat
(loop (force in)))))
(print "total lines read: " (await (mail 'writer #t)))
))
(coroutine 'writer (lambda ()
(let loop ((n 0))
(define line (await (mail 'reader #t)))
(if (eof? line)
then
(define envelope (wait-mail)) ; wait for a request
(mail (ref envelope 1) n) ; send a lines count to caller
else
(print "read line: " line)
(loop (+ n 1))))))
</syntaxhighlight>
An input.txt:
<pre>The world was young, the mountains green,
No stain yet on the Moon was seen,
No words were laid on stream or stone
When Durin woke and walked alone.
He named the nameless hills and dells;
He drank from yet untasted wells;
He stooped and looked in Mirrormere,
And saw a crown of stars appear,
As gems upon a silver thread,
Above the shadows of his head.
</pre>
{{Out}}
<pre>read line: The world was young, the mountains green,
read line: No stain yet on the Moon was seen,
read line: No words were laid on stream or stone
read line: When Durin woke and walked alone.
read line: He named the nameless hills and dells;
read line: He drank from yet untasted wells;
read line: He stooped and looked in Mirrormere,
read line: And saw a crown of stars appear,
read line: As gems upon a silver thread,
read line: Above the shadows of his head.
total lines read: 10
</pre>
=={{header|ooRexx}}==
<syntaxhighlight lang="oorexx">
queue = .workqueue~new
input = .stream~new("jabberwocky.txt")
output = .output
reader = .filereader~new(input, queue)
writer = .filewriter~new(output, queue)
::class workQueue
::method init
expose queue stopped actionpending
queue = .queue~new
stopped = .false
actionPending = .false
-- add an item to the work queue. This is a
-- guarded method, which means this is a synchronized access
::method addItem guarded
expose queue actionPending
use arg item
-- add the item to the queue
queue~queue(item)
-- indicate there's something new. This is a condition variable
-- that any will wake up any thread that's waiting on access. They'll
-- be able to get access once we exit
actionPending = .true
-- another method for coordinating access with the other thread. This indicates
-- it is time to shut down
::method stop guarded
expose actionPending stopped
-- indicate this has been stopped and also flip the condition variable to
-- wake up any waiters
stopped = .true
actionPending = .true
-- read the next item off of the queue. .nil indicates we've reached
-- the last item on the queue. This is also a guarded method, but we'll use
-- the GUARD ON instruction to wait for work if the queue is currently empty
::method nextItem
expose queue stopped actionPending
-- we might need to loop a little to get an item
do forever
-- if there's something on the queue, pull the front item and return
if \queue~isEmpty then return queue~pull
-- if the other thread says it is done sending is stuff, time to shut down
if stopped then return .nil
-- nothing on the queue, not stopped yet, so release the guard and wait until
-- there's something pending to work on.
guard on when actionPending
end
-- one half of the synchronization effort. This will read lines and
-- add them to the work queue. The thread will terminate once we hit end-of-file
::class filereader
::method init
-- accept a generic stream...the data source need not be a file
use arg stream, queue
reply -- now multithreaded
signal on notready
loop forever
queue~addItem(stream~linein)
end
-- we come here on an EOF condition. Indicate we're done and terminate
-- the thread
notready:
queue~stop
-- the other end of this. This class will read lines from a work queue
-- and write it to a stream
::class filewriter
::method init
-- accept a generic stream...the data source need not be a file
use arg stream, queue
reply -- now multithreaded
loop forever
item = queue~nextItem
-- .nil means last item received
if item == .nil then return
-- write to the stream
stream~lineout(item)
end
</syntaxhighlight>
=={{header|Oz}}==
<
%% Helper function to read a file lazily.
%% Returns a lazy list of lines.
Line 511 ⟶ 2,013:
%% Sync on Count and print its value.
{Wait Count}
{Show Count}</
=={{header|Perl}}==
<
use Thread::Queue qw();
Line 546 ⟶ 2,048:
$reader->join;
$printer->join;</
=={{header|Phix}}==
Busy wait version (using threads) - the distribution file also contains single step-lock and queue-less versions of this code.
<!--<syntaxhighlight lang="phix">(notonline)-->
<span style="color: #000080;font-style:italic;">-- demo\rosetta\Synchronous_concurrency.exw</span>
<span style="color: #008080;">without</span> <span style="color: #008080;">js</span> <span style="color: #000080;font-style:italic;">-- threads, file i/o, command_line()</span>
<span style="color: #004080;">string</span> <span style="color: #000000;">filename</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">substitute</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">command_line</span><span style="color: #0000FF;">()[</span><span style="color: #000000;">2</span><span style="color: #0000FF;">],</span><span style="color: #008000;">".exe"</span><span style="color: #0000FF;">,</span><span style="color: #008000;">".exw"</span><span style="color: #0000FF;">)</span>
<span style="color: #004080;">atom</span> <span style="color: #000000;">frThread</span><span style="color: #0000FF;">,</span> <span style="color: #000080;font-style:italic;">-- file reader thread</span>
<span style="color: #000000;">lcThread</span> <span style="color: #000080;font-style:italic;">-- line counter thread</span>
<span style="color: #004080;">sequence</span> <span style="color: #000000;">queue</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{}</span>
<span style="color: #004080;">integer</span> <span style="color: #000000;">qlock</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">init_cs</span><span style="color: #0000FF;">(),</span>
<span style="color: #000000;">linecount</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">1</span>
<span style="color: #008080;">procedure</span> <span style="color: #000000;">readfile</span><span style="color: #0000FF;">()</span>
<span style="color: #004080;">integer</span> <span style="color: #000000;">fn</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">open</span><span style="color: #0000FF;">(</span><span style="color: #000000;">filename</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"r"</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">while</span> <span style="color: #000000;">1</span> <span style="color: #008080;">do</span>
<span style="color: #004080;">object</span> <span style="color: #000000;">line</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">gets</span><span style="color: #0000FF;">(</span><span style="color: #000000;">fn</span><span style="color: #0000FF;">)</span>
<span style="color: #7060A8;">enter_cs</span><span style="color: #0000FF;">(</span><span style="color: #000000;">qlock</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">queue</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">append</span><span style="color: #0000FF;">(</span><span style="color: #000000;">queue</span><span style="color: #0000FF;">,</span><span style="color: #000000;">line</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">line</span> <span style="color: #0000FF;">=</span> <span style="color: #004080;">atom</span><span style="color: #0000FF;">(</span><span style="color: #000000;">line</span><span style="color: #0000FF;">)</span> <span style="color: #000080;font-style:italic;">-- kill refcount!</span>
<span style="color: #7060A8;">leave_cs</span><span style="color: #0000FF;">(</span><span style="color: #000000;">qlock</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">line</span> <span style="color: #008080;">then</span> <span style="color: #008080;">exit</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
<span style="color: #7060A8;">close</span><span style="color: #0000FF;">(</span><span style="color: #000000;">fn</span><span style="color: #0000FF;">)</span>
<span style="color: #7060A8;">wait_thread</span><span style="color: #0000FF;">(</span><span style="color: #000000;">lcThread</span><span style="color: #0000FF;">)</span>
<span style="color: #7060A8;">printf</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"Lines read: %d\n"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">linecount</span><span style="color: #0000FF;">)</span>
<span style="color: #7060A8;">exit_thread</span><span style="color: #0000FF;">(</span><span style="color: #000000;">0</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;">countlines</span><span style="color: #0000FF;">()</span>
<span style="color: #000000;">linecount</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">0</span>
<span style="color: #008080;">while</span> <span style="color: #000000;">1</span> <span style="color: #008080;">do</span>
<span style="color: #7060A8;">enter_cs</span><span style="color: #0000FF;">(</span><span style="color: #000000;">qlock</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">if</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">queue</span><span style="color: #0000FF;">)=</span><span style="color: #000000;">0</span> <span style="color: #008080;">then</span>
<span style="color: #7060A8;">leave_cs</span><span style="color: #0000FF;">(</span><span style="color: #000000;">qlock</span><span style="color: #0000FF;">)</span>
<span style="color: #000080;font-style:italic;">-- sleep(0.1)</span>
<span style="color: #008080;">else</span>
<span style="color: #004080;">object</span> <span style="color: #000000;">line</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">queue</span><span style="color: #0000FF;">[</span><span style="color: #000000;">1</span><span style="color: #0000FF;">]</span>
<span style="color: #000000;">queue</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">queue</span><span style="color: #0000FF;">[</span><span style="color: #000000;">2</span><span style="color: #0000FF;">..$]</span>
<span style="color: #7060A8;">leave_cs</span><span style="color: #0000FF;">(</span><span style="color: #000000;">qlock</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">if</span> <span style="color: #004080;">atom</span><span style="color: #0000FF;">(</span><span style="color: #000000;">line</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">then</span> <span style="color: #008080;">exit</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #000080;font-style:italic;">-- ?line</span>
<span style="color: #000000;">linecount</span> <span style="color: #0000FF;">+=</span> <span style="color: #000000;">1</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
<span style="color: #7060A8;">exit_thread</span><span style="color: #0000FF;">(</span><span style="color: #000000;">0</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">procedure</span>
<span style="color: #000000;">lcThread</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">create_thread</span><span style="color: #0000FF;">(</span><span style="color: #000000;">countlines</span><span style="color: #0000FF;">,{})</span>
<span style="color: #000000;">frThread</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">create_thread</span><span style="color: #0000FF;">(</span><span style="color: #000000;">readfile</span><span style="color: #0000FF;">,{})</span>
<span style="color: #7060A8;">wait_thread</span><span style="color: #0000FF;">(</span><span style="color: #000000;">frThread</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"</span><span style="color: #0000FF;">)</span>
<span style="color: #0000FF;">{}</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">wait_key</span><span style="color: #0000FF;">()</span>
<!--</syntaxhighlight>-->
=={{header|PicoLisp}}==
PicoLisp has no threads, but synchronous background tasks and asynchronous
signal handlers, or coroutines.
===Using background tasks and signals===
The following two tasks communicate via UDP, so in fact they don't need to run
within the same process and not even the same machine. "input.txt" would rather
be a device (like a named pipe or socket) than a plain file.
<syntaxhighlight lang="picolisp"># Reading task (synchronous)
(task (open "input.txt")
(let Fd @
(if (in Fd (line T)) # More lines?
(udp "localhost" 4444 @) # Yes: Send next line
(task (port T 4445) # Else install handler
(prinl (udp @) " lines") # to receive and print count
(task (close @)) )
(udp "localhost" 4444 T) # Send 'T' for "Done"
(task (close Fd)) ) ) ) # Stop the task
# Printing task (asynchronous)
(sigio (setq "Sock" (port T 4444))
(job '((Cnt . 0))
(let? X (udp "Sock")
(if (=T X) # Done?
(prog
(udp "localhost" 4445 Cnt) # Yes: Send count
(sigio (close "Sock")) ) # and stop the task
(println X) # Else print line to stdout
(inc 'Cnt) ) ) ) ) # and increment count</syntaxhighlight>
If the two cases of 'sigio' in the printing task are replaced with 'task',
that task would also be synchronous. The resulting behavior is the same.
===Using coroutines===
Coroutines are available only in the 64-bit version.
<syntaxhighlight lang="picolisp">(co 'unit1
(yield) # Allow 'unit2' to start
(in "input.txt" # Read the file
(while (line T) # Send each line
(yield @ 'unit2) ) ) # to 'unit2'
(prinl
(yield NIL 'unit2) # Send 'NIL' for "Done", receive count
" lines" ) )
(co 'unit2
(let Cnt 0 # Init counter
(while (yield NIL 'unit1) # Receive line
(println @) # Print it
(inc 'Cnt) ) # Increment count
(yield Cnt 'unit1) ) ) # Send count to 'unit1'</syntaxhighlight>
=={{header|Pony}}==
Pony has concurrency baked into the language in the form of the actor model:
<syntaxhighlight lang="pony">use "files"
actor Main
let _env: Env // The environment contains stdout, so we save it here
new create(env: Env) =>
_env = env
let printer: Printer tag = Printer(env)
try
let path = FilePath(env.root as AmbientAuth, "input.txt")? // this may fail, hence the ?
let file = File.open(path)
for line in FileLines(file) do
printer(line) // sugar for "printer.apply(line)"
end
end
printer.done(this)
be finish(count: USize) =>
_env.out.print("Printed: " + count.string() + " lines")
actor Printer
let _env: Env
var _count: USize = 0
new create(env: Env) => _env = env
be apply(line: String) =>
_count = _count + 1
_env.out.print(line)
be done(main: Main tag) => main.finish(_count)</syntaxhighlight>
Actors are scheduled asynchronously, but messages (implemented via the behaviours) are guaranteed to arrive in causal ordering.
=={{header|PureBasic}}==
PureBasic uses Semaphores and Mutex's to coordinate threads.
<syntaxhighlight lang="purebasic">Enumeration
#Write
#Done
EndEnumeration
Structure commblock
txtline.s
Order.i
EndStructure
Global MessageSent=CreateSemaphore()
Global LineWritten=CreateSemaphore()
Global LinesWritten, com.commblock
Procedure Writer(arg)
Repeat
WaitSemaphore(MessageSent)
If com\Order=#Write
PrintN(com\txtline)
LinesWritten+1
EndIf
SignalSemaphore(LineWritten)
Until com\Order=#Done
EndProcedure
Procedure Reader(arg)
Protected File=ReadFile(#PB_Any,OpenFileRequester("","input.txt","",0))
While file And Not Eof(file)
com\txtline=ReadString(File)
com\Order=#Write
SignalSemaphore(MessageSent)
WaitSemaphore(LineWritten)
Wend
com\Order=#Done
SignalSemaphore(MessageSent)
WaitSemaphore(LineWritten)
PrintN(Str(LinesWritten)+" lines written.")
EndProcedure
If OpenConsole()
Define Thread1=CreateThread(@Reader(),0)
Define Thread2=CreateThread(@Writer(),0)
WaitThread(Thread1) And WaitThread(Thread2)
Print("Press Enter to exit"):Input()
EndIf</syntaxhighlight>
=={{header|Python}}==
Notes: instead of hardcoding the input and output files in the units, each unit is created with a file and read or write the given file.
<
from Queue import Queue
from threading import Thread
Line 581 ⟶ 2,275:
writer.start()
reader.join()
writer.join()</
===Using generators===
{{trans|Ruby}}
<syntaxhighlight lang="python">count = 0
def reader():
for line in open('input.txt'):
yield line.rstrip()
print('Printed %d lines.' % count)
r = reader()
# printer
for line in r:
print(line)
count += 1</syntaxhighlight>
Note that the above accesses a variable from both paths of execution. To be more in the spirit of the task, we can actually communicate the count from the printer to the reader:
{{works with|Python|2.5+}}
<syntaxhighlight lang="python">def reader():
for line in open('input.txt'):
yield line.rstrip()
count = yield None
print('Printed %d lines.' % count)
r = reader()
# printer
for count, line in enumerate(r):
if line is None:
break
print(line)
try:
r.send(count)
except StopIteration:
pass</syntaxhighlight>
=={{header|Racket}}==
Using thread mailboxes for communication between threads:
<syntaxhighlight lang="racket">
(define (reader)
(for ([line (in-lines (open-input-file "input.txt"))])
(thread-send printer-thread line))
(thread-send printer-thread eof)
(printf "Number of lines: ~a\n" (thread-receive)))
(define (printer)
(thread-send reader-thread
(for/sum ([line (in-producer thread-receive eof)])
(displayln line)
1)))
(define printer-thread (thread printer))
(define reader-thread (thread reader))
(for-each thread-wait
(list printer-thread reader-thread))
</syntaxhighlight>
Using synchronous channels for communication between threads:
<syntaxhighlight lang="racket">
(define (reader out-ch result-ch)
(for ([line (in-lines (open-input-file "input.txt"))])
(channel-put out-ch line))
(channel-put out-ch eof)
(printf "Number of lines: ~a\n" (channel-get result-ch)))
(define (printer in-ch result-ch)
(channel-put result-ch
(for/sum ([line (in-producer channel-get eof in-ch)])
(displayln line)
1)))
(define lines-ch (make-channel))
(define result-ch (make-channel))
(define printer-thread (thread (lambda () (printer lines-ch result-ch))))
(define reader-thread (thread (lambda () (reader lines-ch result-ch))))
(for-each thread-wait
(list printer-thread reader-thread))
</syntaxhighlight>
=={{header|Raku}}==
(formerly Perl 6)
{{works with|rakudo|2013-02-27}}
<syntaxhighlight lang="raku" line>sub MAIN ($infile) {
$infile.IO.lines ==> printer() ==> my $count;
say "printed $count lines";
}
sub printer(*@lines) {
my $lines;
for @lines {
.say;
++$lines;
}
$lines;
}</syntaxhighlight>
Concurrent units are established by use of the feed operator, which works much like an in-process object pipe. Since the final feed goes to a variable declaration that belongs to the outer thread, it serves as a backchannel from the printer thread. In this case the outer thread signals the desire for a line count by terminating the pipe to the printing thread.
(Note: soon these will be implemented with real threads in Raku, but this is currently emulated with coroutine semantics, aka lazy lists.)
=={{header|Raven}}==
<
class Queue
Line 611 ⟶ 2,406:
reader as r
writer as w</
=={{header|
The task is to refactor this program to use two concurrent units.
<syntaxhighlight lang="ruby">count = 0
IO.foreach("input.txt") { |line| print line; count += 1 }
puts "Printed #{count} lines."</syntaxhighlight>
The above program has no concurrency, because the printer is a block <tt>{ |line| print line; count += 1 }</tt> that can print only one line. (The reader calls block more than one time.) After the refactoring, the printer will print all lines, and the program will jump between the reader and the printer. For the refactoring, Fibers might be best, Continuations work if our Ruby is too old for Fibers, and Threads are another alternative.
----
'''Fibers.''' Ruby 1.9 gives Fiber to us. ''Fibers provide concurrency.'' Each fiber has its own stack (to hold nested function calls). A pair of fibers has a boss-vassal relationship: the boss fiber calls <tt>vassal.resume</tt> to jump to the vassal, and the vassal fiber calls <tt>Fiber.yield</tt> to jump to the boss.
{{works with|Ruby|1.9}}
<syntaxhighlight lang="ruby">count = 0
reader = Fiber.new do
IO.foreach("input.txt") { |line| Fiber.yield line }
puts "Printed #{count} lines."
nil
end
# printer
while line = reader.resume
print line
count += 1
end</syntaxhighlight>
* We create a fiber as the reader, and we use the current fiber as the printer.
* Our reader is a [[generator]], because <tt>reader.resume</tt> generates a <tt>line</tt>, and <tt>Fiber.yield</tt> passes the generated value.
* This generator allows <tt>Fiber.yield</tt> inside nested function calls (because a fiber has its own stack). We nested three calls: we have <tt>Fiber.yield</tt> inside our line block, inside <tt>IO.foreach</tt>, inside our fiber block.
* Because the reader and printer are in the same process, they can share the <tt>count</tt> variable. An alternate way is to use <tt>reader.resume(count)</tt> to pass the count, so <tt>Fiber.yield</tt> would return the count.
* If <tt>IO.foreach</tt> raises an IO error, then the reader dies, and <tt>reader.resume</tt> raises the same error in the printer. This is what we want. If we run this program with no <tt>input.txt</tt> file, then we see the error.
----
'''Continuations.''' Ruby 1.8 gives Continuation to us. (Ruby 1.9 still gives Continuation if we <tt>require 'continuation'</tt> from the standard library.) The trick is that you can continue a function call after you leave it. ''Continuations can provide concurrency.'' The problem is that continuations make spaghetti code with very confusing control flow.
{{libheader|continuation}}
<syntaxhighlight lang="ruby">require 'continuation' unless defined? Continuation
count = 0
reader = proc do |cont|
IO.foreach("input.txt") { |line| cont = callcc { |cc| cont[cc, line] }}
puts "Printed #{count} lines."
cont[nil]
end
# printer
while array = callcc { |cc| reader[cc] }
reader, line = array
print line
count += 1
end</syntaxhighlight>
* The above program uses continuations almost like fibers. The reader continues the printer, and the printer continues the reader.
* The first call to <tt>reader[c]</tt> uses <tt>Proc#[]</tt> to start the reader; but later calls to <tt>reader[c]</tt> use <tt>Continuation#[]</tt> to continue the reader.
* The reader and printer share the same stack. The control flow when <tt>IO.foreach</tt> raises an IO error is very strange. The reader dies, and ''the original call to Proc#[]'' raises the same error in the printer.
----
'''Threads.''' Both Ruby 1.8 and Ruby 1.9 give Thread to us. ''Threads provide preemptive concurrency.'' The scheduler preempts threads and switches between threads, seemingly at random. Threads seem worse than continuations, because threads have unpredictable control flow, but we can use a Queue to restore some order. We use Thread with Queue.
{{libheader|thread}}
<syntaxhighlight lang="ruby">require 'thread'
counts = Queue.new
lines = Queue.new
reader = Thread.new do
begin
File.foreach("input.txt") { |line| lines << line }
lines << :EOF
puts "Printed #{counts.pop} lines."
ensure
lines << nil
end
end
# writer
count = 0
while line = lines.pop
case line
when String
print line
count += 1
when :EOF
counts << count
end
end
reader.join</syntaxhighlight>
* We create a thread as the reader, and use the current thread as the writer.
* If a thread tries to pop an empty queue, then the thread waits until some other thread queues something.
* The queue of <tt>lines</tt> can become long; the worst case allows the reader to read the entire file before the printer pops the first line! If you wanted to prevent a long queue, a <tt>SizedQueue.new(5)</tt> would hold only 5 elements.
* If <tt>IO.reader</tt> raises an IO error, then the reader dies. The writer would deadlock on an empty queue after the reader dies. To prevent this deadlock, the reader ensures to queue a final <tt>nil</tt> before it dies. The writer uses this <tt>nil</tt> to break its loop and call <tt>reader.join</tt>. If the reader dies with an IO error, then <tt>reader.join</tt> raises the same error.
=={{header|Rust}}==
{{works with|rustc 1.46.0 (04488afe3 2020-08-24)|}}
<syntaxhighlight lang="rust">use std::fs::File;
use std::io::BufRead;
use std::io::BufReader;
use std::sync::mpsc::{channel, sync_channel};
use std::thread;
fn main() {
// The reader sends lines to the writer via an async channel, so the reader is never blocked.
let (reader_send, writer_recv) = channel();
// The writer sends the final count via a blocking channel with bound 0,
// meaning the buffer is exactly the size of the result.
let (writer_send, reader_recv) = sync_channel(0);
// Define the work the reader will do.
let reader_work = move || {
let file = File::open("input.txt").expect("Failed to open input.txt");
let reader = BufReader::new(file);
for line in reader.lines() {
match line {
Ok(msg) => reader_send
.send(msg)
.expect("Failed to send via the channel"),
Err(e) => println!("{}", e),
}
}
// Dropping the sender disconnects it and tells the receiver the connection is closed.
drop(reader_send);
// Now that we've sent all the lines,
// block until the writer gives us the final count.
let count = reader_recv
.recv()
.expect("Failed to receive count from printer.");
println!("{}", count);
};
// Define the work the writer will do.
let writer_work = move || {
let mut line_count = 0;
loop {
match writer_recv.recv() {
Ok(msg) => {
println!("{}", msg);
line_count += 1;
}
Err(_) => break, // indicates the connection has been closed by the sender.
}
}
// Send the final count back to the reader.
writer_send
.send(line_count)
.expect("Failed to send line count from writer.");
drop(writer_send);
};
// Spawn each as a thread.
let reader_handle = thread::spawn(reader_work);
thread::spawn(writer_work);
reader_handle
.join()
.expect("Failed to join the reader thread.");
}</syntaxhighlight>
=={{header|Scala}}==
[[Category:Scala examples needing attention]]
A possible implementation using Actors
<syntaxhighlight lang="scala">case class HowMany(asker: Actor)
val printer = actor {
var count = 0
receive
case HowMany(asker: Actor) => asker ! count; exit()
}
}
}
def reader(printer: Actor) {
scala.io.Source.fromFile("c:\\input.txt").getLines foreach { printer ! _ }
printer ! HowMany(
actor {
receive {
}
})
}
reader(printer)</
=={{header|Swift}}==
Using Grand Central Dispatch and NSNotificationCenter<br><br>
'''Reader.swift'''
<syntaxhighlight lang="swift">//
// Reader.swift
//
import Foundation
class Reader: NSObject {
let inputPath = "~/Desktop/input.txt".stringByExpandingTildeInPath
var gotNumberOfLines = false
override init() {
super.init()
NSNotificationCenter.defaultCenter().addObserver(self, selector: "linesPrinted:",
name: "LinesPrinted", object: nil)
}
deinit {
NSNotificationCenter.defaultCenter().removeObserver(self)
}
// Selector for the number of lines printed
func linesPrinted(not:NSNotification) {
println(not.object!)
self.gotNumberOfLines = true
exit(0)
}
func readFile() {
var err:NSError?
let fileString = NSString(contentsOfFile: self.inputPath,
encoding: NSUTF8StringEncoding, error: &err)
if let lines = fileString?.componentsSeparatedByString("\n") {
for line in lines {
NSNotificationCenter.defaultCenter().postNotificationName("Line", object: line)
}
NSNotificationCenter.defaultCenter().postNotificationName("LineNumberRequest", object: nil)
while !self.gotNumberOfLines {
sleep(1 as UInt32)
}
}
}
}</syntaxhighlight>
'''Printer.swift'''
<syntaxhighlight lang="swift">//
// Printer.swift
//
import Foundation
class Printer: NSObject {
var numberOfLines = 0
var gotRequestLineNumber = false
override init() {
super.init()
NSNotificationCenter.defaultCenter().addObserver(self, selector: "gotLine:",
name: "Line", object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: "lineNumberRequest:",
name: "LineNumberRequest", object: nil)
}
deinit {
NSNotificationCenter.defaultCenter().removeObserver(self)
}
func gotLine(not:NSNotification) {
println(not.object!)
self.numberOfLines++
}
func lineNumberRequest(not:NSNotification) {
self.gotRequestLineNumber = true
NSNotificationCenter.defaultCenter().postNotificationName("LinesPrinted", object: self.numberOfLines)
}
func waitForLines() {
while !self.gotRequestLineNumber {
sleep(1 as UInt32)
}
}
}</syntaxhighlight>
'''main.swift'''
<syntaxhighlight lang="swift">//
// main.swift
//
import Foundation
dispatch_async(dispatch_get_global_queue(0, 0)) {
let printer = Printer()
printer.waitForLines()
}
dispatch_async(dispatch_get_global_queue(0, 0)) {
let reader = Reader()
reader.readFile()
}
CFRunLoopRun()
</syntaxhighlight>
=={{header|SystemVerilog}}==
<syntaxhighlight lang="systemverilog">program main;
mailbox#(bit) p2c_cmd = new;
mailbox#(string) p2c_data = new;
mailbox#(int) c2p_data = new;
initial begin
int fh = $fopen("input.txt", "r");
string line;
int count;
while ($fgets(line, fh)) begin
p2c_cmd.put(0);
p2c_data.put(line);
end
p2c_cmd.put(1);
c2p_data.get(count);
$display( "COUNT: %0d", count );
end
initial begin
bit done;
int count;
while (!done) begin
p2c_cmd.get(done);
if (done) begin
c2p_data.put(count);
end
else begin
string line;
p2c_data.get(line);
$display( "LINE: %s", line);
count++;
end
end
end
endprogram</syntaxhighlight>
=={{header|Tcl}}==
Uses the Thread package.
<
# Define the input thread
Line 670 ⟶ 2,782:
# Connect everything together and start the processing
thread::send $input [list readFile "input.txt" $output]</
=={{header|TXR}}==
Using delimited-continuation-based <code>obtain</code> and <code>yield-from</code> to simulate co-routines, wrapped in some OOP. A <code>thread</code> base class is derived into <code>consumer</code> and <code>producer</code>, both of which provide <code>run</code> methods. The <code>consumer</code> has a counter also, and <code>producer</code> holds a reference to a <code>consumer</code>.
When the objects are instantiated, their co-routines auto-start, thanks to the <code>:postinit</code> hook.
To get things going, we resume the producer via <code>pro.(resume)</code>, because we started that in a suspended state. This is actually not necessary; if we remove the <code>suspended t</code> from the <code>new</code> expression which instantiates the producer, we can remove this line. However, this means that the body of the <code>let</code> doesn't receive control. The producer finishes producing and then the <code>pro</code> variable is bound, and the final <code>(put-line ...)</code> expression evaluates. Starting the producer suspended lets us insert some logic prior to dispatching the producer. We implicitly start the consumer, though, because it immediately suspends to wait for an item, saving its context in a continuation and relinquishing control.
<syntaxhighlight lang="txrlisp">(defstruct thread nil
suspended
cont
(:method resume (self)
[self.cont])
(:method give (self item)
[self.cont item])
(:method get (self)
(yield-from run nil))
(:method start (self)
(set self.cont (obtain self.(run)))
(unless self.suspended
self.(resume)))
(:postinit (self)
self.(start)))
(defstruct consumer thread
(count 0)
(:method run (self)
(whilet ((item self.(get)))
(prinl item)
(inc self.count))))
(defstruct producer thread
consumer
(:method run (self)
(whilet ((line (get-line)))
self.consumer.(give line))))
(let* ((con (new consumer))
(pro (new producer suspended t consumer con)))
pro.(resume)
(put-line `count = @{con.count}`))</syntaxhighlight>
=={{header|UnixPipes}}==
Line 681 ⟶ 2,835:
forks.
<
cat file | tee >(wc -l > node ) | cat - node</
=={{header|Visual Basic .NET}}==
This can be improved by adding a blocking Dequeue instead of spinning on TryDequeue.
<
Module Module1
Line 751 ⟶ 2,905:
End SyncLock
End Sub
End Class</
=={{header|Wren}}==
<syntaxhighlight lang="wren">import "io" for File
var EOT = "\x04"
var readLines = Fiber.new { |fileName|
var file = File.open(fileName)
var offset = 0
var line = ""
while (true) {
var b = file.readBytes(1, offset)
offset = offset + 1
if (b == "\n") {
Fiber.yield(line)
line = "" // reset line variable
} else if (b == "\r") { // Windows
// wait for following "\n"
} else if (b == "") { // end of stream
var numLines = Fiber.yield(EOT)
System.print("Number of lines read = %(numLines)")
break
} else {
line = line + b
}
}
file.close()
}
var numLines = 0
while(true) {
var line = readLines.call("input.txt")
if (line != EOT) {
System.print(line)
numLines = numLines + 1
} else {
readLines.call(numLines)
break
}
}</syntaxhighlight>
{{out}}
input.txt contains the following 4 lines:
<pre>
line 1
line 2
line 3
line 4
Number of lines read = 4
</pre>
=={{header|zkl}}==
<syntaxhighlight lang="zkl">fcn reader(fileName,out){
n:=0; foreach line in (File(fileName)) { out.write(line); n+=1; }
out.close(); // signal done
Atomic.waitFor(out.Property("isOpen")); // wait for other thread to reopen Pipe
out.write(n);
}
fcn writer(in){
Utils.zipWith(fcn(n,line){ "%3d: %s".fmt(n,line).print() },[1..],in);
in.open(); // signal other thread to send num lines read
println("Other thread read ",in.read()," lines");
}
p:=Thread.Pipe(); // NOT Unix pipes, thread safe channel between threads
reader.launch("input.txt",p);
writer.future(p).noop(); // noop forces eval, ie sleep until writer finished</syntaxhighlight>
Light on error handling, easily fixed.
{{out}}
input.txt is just a code file
<pre>
1: to := Thread.Pipe(); from := Thread.Pipe();
2: a:=fcn(to,from){
...
15: }.launch(to,from);
16:
17: a.noop();
Other thread read 17 lines
</pre>
{{omit from|AWK}}
{{omit from|GUISS|This can only be done, if there are apps installed that do this}}
{{omit from|TI-83 BASIC}} {{omit from|TI-89 BASIC}} <!-- Does not have concurrency or background processes. -->
{{omit from|M4}}
{{omit from|Maxima}}
{{omit from|PARI/GP}}
{{omit from|Retro}}
{{omit from|ZX Spectrum Basic|Does not support concurrency.}}
| |||