source: tests/concurrent/park/force_preempt.cfa@ a8078eef

#include <thread.hfa>
#include <fstream.hfa>

volatile int global = 0;

thread Poller {};
void main(Poller & this) {
        while(true) {
                waitfor( ^?{} : this ) {
                        break;
                } or else {
                        global = (global + 1) % 10;
                        yield();
                }
        }
}

thread Waiter;
thread Waiter {};


volatile int count = 0;

void main(Waiter & this) {
        // Get a unique id
        int id = __atomic_fetch_add(&count, 1, __ATOMIC_SEQ_CST);

        for(int i = 0; i < 5; i++) {
                // Unpark this thread, don't force a yield
                sout | id | "Calling unpark" | i;
                unpark(this);

                // Force a preemption before the call to park
                int prev = global;
                while(prev == global) {}

                // Park this thread,
                sout | id | "Parking" | i;
                park();
                sout | id | "Unparked" | i;
        }
}

int main() {
        Poller p;
        {
                Waiter waiters[5];
        }
}