Defined in header <threads.h>
int cnd_wait( cnd_t* cond, mtx_t* mutex );
(since C11)

Atomically unlocks the mutex pointed to by mutex and blocks on the condition variable pointed to by cond until the thread is signalled by cnd_signal or cnd_broadcast, or until a spurious wake-up occurs. The mutex is locked again before the function returns.

The behavior is undefined if the mutex is not already locked by the calling thread.


cond - pointer to the condition variable to block on
mutex - pointer to the mutex to unlock for the duration of the block

Return value

thrd_success if successful, thrd_error otherwise.


  • C17 standard (ISO/IEC 9899:2018):
    • The cnd_wait function (p: 277)
  • C11 standard (ISO/IEC 9899:2011):
    • The cnd_wait function (p: 380)

See also

blocks on a condition variable, with a timeout
C++ documentation for condition_variable::wait
C++ documentation for condition_variable_any::wait

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