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CLASS::Semaphore
categories::Scheduling
summary::control parallel execution of threads
CLASSMETHODS::
method::new
Create a new instance, set the maximum number of running threads (default: 1).
INSTANCEMETHODS::
method::count
Determines the number of running threads.
method::clear
Remove any reference to threads, but do not reschedule any pending ones.
method::wait
Stop current thread if already too many are running, otherwise continue.
method::signal
Unblock the semaphore, reschedule next pending thread.
EXAMPLES::
code::
// allow only one thread
(
c = Semaphore(1);
fork {
c.wait;
"thread 1> now I am doing something for 10 seconds. Block the semaphore meanwhile.".postln;
10.wait;
c.signal;
"thread 1> ok, done. Release the semaphore.".postln;
};
fork {
3.0.rand.wait;
"thread 2> I would like to go on, if I may.".postln;
c.wait; // may I?
"thread 2> this took until the other thread has released the semaphore. "
"Blocking for 4 seconds.".postln;
4.wait;
"thread 2> ok, done. Releasing the semaphore".postln;
c.signal;
};
fork {
4.wait;
"thread 3> I, too, would like to go on, if I may.".postln;
c.wait; // may I?
"thread 3> this took until both other threads had released the semaphore.".postln;
c.signal;
};
)
::
code::
// allow two threads at a time.
(
c = Semaphore(2);
fork {
c.wait;
"thread 1> now I am doing something for 20 seconds. Block the semaphore.".postln;
10.wait;
"thread 1> ok, done. Releasing the semaphore".postln;
c.signal;
};
fork {
rrand(3.0, 5.0).wait;
"thread 2> I would like to go on, if I may.".postln;
if(c.count <= 0) { "thread 3> ok, then I wait ...".postln };
c.wait; // may I?
"thread 1> ok, going ahead.".postln;
17.wait;
"thread 2> ok, done. Releasing the semaphore".postln;
c.signal;
};
fork {
6.wait;
"thread 3> I, too, would like to go on, if I may.".postln;
if(c.count <= 0) { "thread 3> ok, then I wait ...".postln };
c.wait; // may I?
"thread 3> ok, this took until the first thread had released the semaphore. "
"Ok, doing something for 4 seconds. Block the semaphore".postln;
4.wait;
"Releasing the semaphore.".postln;
c.signal;
};
fork {
7.wait;
"thread 4> Me, the fourth one, would like to go on, if I may.".postln;
if(c.count <= 0) { "thread 4> ok, then I wait ...".postln };
c.wait; // may I?
"thread 4> ok, this took until the third thread had released the semaphore. "
"Ok, doing something for 3 seconds. Block the semaphore".postln;
3.wait;
"Releasing the semaphore.".postln;
c.signal;
};
)
::
code::
// grant exclusive access to data to only one thread
// there should never be mixed values in the data array
(
var data, useAndModify;
data = [1, 2, 3];
c = Semaphore(1);
// c = Semaphore(2); use this to test how it would behave without exclusive access.
useAndModify = { |newData, who|
postln(who + "trying to get blocking access.");
if(c.count <= 0) { who + "ok, then I wait ...".postln };
c.wait; // may I access? if not, I wait. if yes, disallow others.
"\n".post;
(who + "continuing...").postln;
data.do({ |x|
0.1.wait;
postln(who + x);
});
"\n".post;
newData.do { |x, i| data[i] = x };
postln(who + "rewriting data to:" + newData);
postln(who + "releasing");
c.signal; // allow others access again
};
// e.g. set the values to integers
u = Routine {
inf.do { |i|
useAndModify.value([100, 200, 300], "thread 1>");
rrand(1, 3).wait;
}
};
// e.g. set the values to floats
k = Routine {
0.5.wait;
inf.do { |i|
useAndModify.value([pi, 0.5pi, 2pi], "thread 2>");
rrand(1, 5).wait;
}
};
u.play;
k.play;
);
::
|
