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Resolve race condition in scheduler (Issue #83) #89

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Resolve race condition in scheduler (Issue #83) #89

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27 changes: 25 additions & 2 deletions include/parlay/scheduler.h
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Original file line number Diff line number Diff line change
Expand Up @@ -294,10 +294,33 @@ struct scheduler {
}

// Wait until notified to wake up
//
// Announce that the worker is being put to sleep/atomic_wait by decrementing num_awake_workers
// Before sleeping, perform one further round of steals
// - if job found:
// increment num_awake_workers, and DON'T atomic_wait, start working on job
// - if no job found:
// perform atomic_wait
void wait_for_work() {
auto orig_val = wake_up_counter.load();
num_awake_workers.fetch_sub(1);
parlay::atomic_wait(&wake_up_counter, wake_up_counter.load());
num_awake_workers.fetch_add(1);
size_t id = worker_id();
Job* job = nullptr;
for (size_t i = 0; i <= YIELD_FACTOR * num_deques; i++) {
if (finished()) {
num_awake_workers.fetch_add(1);
return;
}
job = try_steal(id);
if(job)
{
num_awake_workers.fetch_add(1);
(*job)();
return;
}
}
parlay::atomic_wait(&wake_up_counter, orig_val);
num_awake_workers.fetch_add(1);
}

#endif
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