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Condition variables must be used inside a while loop (see CON36-C. Wrap functions that can spuriously wake up in a loop for more information). To guarantee liveness, programs must test the while loop condition before invoking the cnd_wait() function. This early test checks whether another thread has already satisfied the condition predicate and has sent a notification. Invoking the cnd_wait() function after the notification has been sent results in indefinite blocking.
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