Annotated Condition Variable Example

Condition *cv;

Lock* cvMx;

int waiter = 0;

void await() {

cvMx->Lock();

waiter = waiter + 1; /* “I’m sleeping” */

cv->Wait(cvMx); /* sleep */

cvMx->Unlock();

}

void awake() {

cvMx->Lock();

if (waiter)

cv->Signal(cvMx);

waiter = waiter - 1;

CvMx->Unlock();

}

Must hold lock when calling Wait.

Wait atomically reacquires lock before returning.

Wait atomically releases lock and sleeps until next Signal.

Association with lock/mutex allows threads to safely manage state related to the sleep/wakeup coordination (e.g., waiters count).