Provided by:
freebsd-manpages_7.0-2_all 
NAME
condvar, cv_init, cv_destroy, cv_wait, cv_wait_sig, cv_wait_unlock,
cv_timedwait, cv_timedwait_sig, cv_signal, cv_broadcast, cv_broadcastpri,
cv_wmesg - kernel condition variable
SYNOPSIS
#include <sys/param.h>
#include <sys/proc.h>
#include <sys/condvar.h>
void
cv_init(struct cv *cvp, const char *desc);
void
cv_destroy(struct cv *cvp);
void
cv_wait(struct cv *cvp, lock);
int
cv_wait_sig(struct cv *cvp, lock);
void
cv_wait_unlock(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);
const char *
cv_wmesg(struct cv *cvp);
DESCRIPTION
Condition variables are used in conjunction with mutexes to wait for
conditions to occur. Condition variables are created with cv_init(),
where cvp is a pointer to space for a struct cv, and desc is a pointer to
a null-terminated character string that describes the condition variable.
Condition variables are destroyed with cv_destroy(). Threads wait on
condition variables by calling cv_wait(), cv_wait_sig(),
cv_wait_unlock(), cv_timedwait(), or cv_timedwait_sig(). Threads unblock
waiters by calling cv_signal() to unblock one waiter, or cv_broadcast()
or cv_broadcastpri() to unblock all waiters. In addition to waking
waiters, cv_broadcastpri() ensures that all of the waiters have a
priority of at least pri by raising the priority of any threads that do
not. cv_wmesg() returns the description string of cvp, as set by the
initial call to cv_init().
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.
The cv_wait_unlock() function does not reacquire the lock before
returning. 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().
RETURN VALUES
If successful, cv_wait_sig(), cv_timedwait(), and cv_timedwait_sig()
return 0. Otherwise, a non-zero error code is returned.
cv_wmesg() returns the description string that was passed to cv_init().
ERRORS
cv_wait_sig() and cv_timedwait_sig() will fail if:
[EINTR] A signal was caught and the system call should be
interrupted.
[ERESTART] A signal was caught and the system call should be
restarted.
cv_timedwait() and cv_timedwait_sig() will fail if:
[EWOULDBLOCK] Timeout expired.
SEE ALSO
locking(9), mtx_pool(9), mutex(9), rwlock(9), sema(9), sleep(9), sx(9)