source: tests/concurrency/park/contention.cfa@ d829c6d

#include <kernel.hfa>
#include <thread.hfa>

__thread drand48_data buffer = { 0 };
int myrand() {
        long int result;
        lrand48_r(&buffer, &result);
        return result;
}


thread Thread {};
void ^?{}(Thread & mutex this) {}

enum Constants { blocked_size = 20 };
Thread * volatile blocked[blocked_size];

void main( Thread & this ) {
        for(int i = 0; i < 1000; i++) {
                int idx = myrand() % blocked_size;
                if(blocked[idx]) {
                        Thread * thrd = __atomic_exchange_n(&blocked[idx], 0p, __ATOMIC_SEQ_CST);
                        unpark( *thrd );
                } else {
                        Thread * thrd = __atomic_exchange_n(&blocked[idx], &this, __ATOMIC_SEQ_CST);
                        unpark( *thrd );
                        park();
                }
        }
        printf("Done\n");
}

// Extra thread to avoid deadlocking
thread Unparker {};

void main( Unparker & this ) {
        while(true) {
                waitfor( ^?{} : this ) {
                        break;
                } or else {
                        int idx = myrand() % blocked_size;
                        Thread * thrd = __atomic_exchange_n(&blocked[idx], 0p, __ATOMIC_SEQ_CST);
                        unpark( *thrd );
                        yield( myrand() % 20 );
                }
        }
        printf("Done Unparker\n");
}


int main() {
        for(i ; blocked_size) {
                blocked[i] = 0p;
        }

        processor p[3];

        Unparker u;
        {
                Thread t[20];
        }
}