Basic thread logic based on condition variables in Poly/ML

thread.ml

(*
 * Tested in Poly/ML. To compile: `polyc thread.ml && ./a.out`
 *
 * Heavily influenced by: http://pages.cs.wisc.edu/~remzi/OSTEP/threads-cv.pdf
 * Poly/ML Thread documentation here: http://www.polyml.org/documentation/Reference/Threads.html
 * Poly/ML Thread implementation here: https://github.com/polyml/polyml/blob/master/basis/Thread.sml
 *)

val done = ref false;
val m = Thread.Mutex.mutex();
val c = Thread.ConditionVar.conditionVar();

fun quit() = let in
    Thread.Mutex.lock(m);
    done := true;
    Thread.ConditionVar.signal(c);
    Thread.Mutex.unlock(m) end;


fun join() = let in
    Thread.Mutex.lock(m);
    while !done = false do let in
        Thread.ConditionVar.wait(c, m) end;
    Thread.Mutex.unlock(m) end;

fun child() = let in
    print "child\n";
    quit() end;

fun main() = let in
    print "parent start\n";
    Thread.Thread.fork(child, []);
    join();
    print "parent end\n" end