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

NAME
     condvar, cv_init, cv_destroy, cv_wait, cv_wait_sig, 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, struct mtx *mp);

     int
     cv_wait_sig(struct cv *cvp, struct mtx *mp);

     int
     cv_timedwait(struct cv *cvp, struct mtx *mp, int timo);

     int
     cv_timedwait_sig(struct cv *cvp, struct mtx *mp, 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_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 prior-
     ity of any threads that do not.  cv_wmesg() returns the description
     string of cvp, as set by the initial call to cv_init().

     A thread must hold mp before calling cv_wait(), cv_wait_sig(),
     cv_timedwait(), or cv_timedwait_sig().  When a thread waits on a condi-
     tion, mp is atomically released before the thread is blocked, then atomi-
     cally reacquired before the function call returns.  All waiters must pass
     the same mp in conjunction with cvp.

     When cv_wait(), cv_wait_sig(), 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]            An unmasked signal was caught.

     [ERESTART]         A masked signal was caught.

     cv_timedwait() and cv_timedwait_sig() will fail if:

     [EWOULDBLOCK]      Timeout expired.

SEE ALSO
     msleep(9), mtx_pool(9), mutex(9), sema(9), sx(9)

FreeBSD 6.2                    December 11, 2000                   FreeBSD 6.2

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

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=condvar&sektion=9&manpath=FreeBSD+6.2-RELEASE>

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