Ubuntu manuals

Provided by: freebsd-manpages_6.2-1_all

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().
      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.
      msleep(9), mtx_pool(9), mutex(9), sema(9), sx(9)