The FreeBSD kernel provides the following 11 functions for working with condition variables:

#include <sys/param.h>
#include <sys/proc.h>
#include <sys/condvar.h>

void
cv_init(struct cv *cvp, const char *d);

const char *
cv_wmesg(struct cv *cvp);

void
cv_wait(struct cv *cvp, lock);

void
cv_wait_unlock(struct cv *cvp, lock);

int
cv_wait_sig(struct cv *cvp, lock);

int
cv_timedwait(struct cv *cvp, lock, int timo);

int
cv_timedwait_sig(struct cv *cvp, lock, int timo);

void
cv_signal(struct cv *cvp);

void
cv_broadcast(struct cv *cvp);

void
cv_broadcastpri(struct cv *cvp, int pri);

void
cv_destroy(struct cv *cvp);

The cv_init function initializes the condition variable cvp. The d argument describes cvp.

The cv_wmesg function gets the description of cvp. This function is primarily used in error reporting.

Threads sleep on cvp by calling cv_wait. The lock argument demands a sleep mutex, sx lock, or rw lock. Threads must hold lock before calling cv_wait. Threads must not sleep on cvp with lock held recursively.

The cv_wait_unlock function is a variant of cv_wait. When threads wake up from sleeping on cvp, they forgo reacquiring lock.

The cv_wait_sig function is identical to cv_wait except that when the caller is asleep it can be woken up by signals. If this occurs, the error code EINTR or ERESTART is returned.

The cv_timedwait function is identical to cv_wait except that the caller sleeps at most timo / hz seconds. If the sleep times out, the error code EWOULDBLOCK is returned.

The cv_timedwait_sig function is like cv_wait_sig and cv_timedwait. The caller can be woken up by signals and sleeps at most timo / hz seconds.

Threads wake up one thread sleeping on cvp by calling cv_signal, and they wake up every thread sleeping on cvp by calling cv_broadcast.

The cv_broadcastpri function is identical to cv_broadcast except that all threads woken up have their priority raised to pri. Threads with a priority higher than pri do not have their priority lowered.

The cv_destroy function destroys the condition variable cvp.