CONDVAR(9)	       FreeBSD Kernel Developer's Manual	    CONDVAR(9)

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 con-
     ditions 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 wait-
     ers, 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.
     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 con-
     junction 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)

FreeBSD 7.2			 June 5, 2007			   FreeBSD 7.2

NAME - SYNOPSIS - DESCRIPTION - RETURN VALUES - ERRORS - SEE ALSO -