Semaphore : Object

// 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;

};

)

// 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;

};

)

// 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;

);