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

     condvar, cv_init, cv_destroy, cv_wait, cv_wait_sig, cv_wait_unlock,
     cv_timedwait, cv_timedwait_sbt, cv_timedwait_sig, cv_timedwait_sig_sbt,
     cv_signal, cv_broadcast, cv_broadcastpri, cv_wmesg - kernel condition

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

     cv_init(struct cv *cvp, const char *desc);

     cv_destroy(struct cv *cvp);

     cv_wait(struct cv *cvp, lock);

     cv_wait_sig(struct cv *cvp, lock);

     cv_wait_unlock(struct cv *cvp, lock);

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

     cv_timedwait_sbt(struct cv *cvp, lock, sbintime_t sbt, sbintime_t pr,
         int flags);

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

     cv_timedwait_sig_sbt(struct cv *cvp, lock, sbintime_t sbt, sbintime_t pr,
         int flags);

     cv_signal(struct cv *cvp);

     cv_broadcast(struct cv *cvp);

     cv_broadcastpri(struct cv *cvp, int pri);

     const char *
     cv_wmesg(struct cv *cvp);

     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.
     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.

     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().

     cv_wait_sig() and cv_timedwait_sig() will fail if:

     [EINTR]            A signal was caught and the system call should be

     [ERESTART]         A signal was caught and the system call should be

     cv_timedwait() and cv_timedwait_sig() will fail if:

     [EWOULDBLOCK]      Timeout expired.

     locking(9), mtx_pool(9), mutex(9), rwlock(9), sema(9), sleep(9), sx(9),

FreeBSD 11.1-RELEASE-p4        February 19, 2013       FreeBSD 11.1-RELEASE-p4
Command Section