Manual Pages  — CONDVAR

The lock argument is a pointer to either a mutex(9), rwlock(9), or sx(9) lock. A mutex(9) argument must be initialized with MTX_DEF and not MTX_SPIN. A thread must hold lock before calling cv_wait(), cv_wait_sig(), cv_wait_unlock(), cv_timedwait(), or cv_timedwait_sig(). When a thread waits on a condition, lock is atomically released before the thread is blocked, then reacquired before the function call returns. In addition, the thread will fully drop the Giant mutex (even if recursed) while the it is suspended and will reacquire the Giant mutex before the function returns. The cv_wait_unlock() function does not reacquire the lock before returning. Note that the Giant mutex may be specified as lock. However, Giant may not be used as lock for the cv_wait_unlock() function. All waiters must pass the same lock in conjunction with cvp.

When cv_wait(), cv_wait_sig(), cv_wait_unlock(), cv_timedwait(), and cv_timedwait_sig() unblock, their calling threads are made runnable. cv_timedwait() and cv_timedwait_sig() wait for at most timo / HZ seconds before being unblocked and returning EWOULDBLOCK; otherwise, they return 0. cv_wait_sig() and cv_timedwait_sig() return prematurely with a value of EINTR or ERESTART if a signal is caught, or 0 if signaled via cv_signal() or cv_broadcast().

cv_timedwait_sbt() and cv_timedwait_sig_sbt() functions take sbt argument instead of timo. It allows to specify relative or absolute unblock time with higher resolution in form of sbintime_t. The parameter pr allows to specify wanted absolute event precision. The parameter flags allows to pass additional callout_reset_sbt() flags.