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System Calls                                    _lwp_cond_wait(2)



NAME
     _lwp_cond_wait, _lwp_cond_timedwait,  _lwp_cond_reltimedwait
     - wait on a condition variable

SYNOPSIS
     #include <sys/lwp.h>

     int _lwp_cond_wait(lwp_cond_t *cvp, lwp_mutex_t *mp);

     int _lwp_cond_timedwait(lwp_cond_t  *cvp,  lwp_mutex_t  *mp,
     timestruc_t *abstime);

     int _lwp_cond_reltimedwait(lwp_cond_t *cvp, lwp_mutex_t *mp,
     timestruc_t *reltime);

DESCRIPTION
     These functions are used to wait for  the  occurrence  of  a
     condition represented by an LWP condition variable. LWP con-
     dition variables must be initialized to 0 before use.

     The _lwp_cond_wait() function atomically  releases  the  LWP
     mutex  pointed  to by mp and causes the calling LWP to block
     on the LWP condition variable pointed to by cvp. The blocked
     LWP     may     be    awakened    by    _lwp_cond_signal(2),
     _lwp_cond_broadcast(2), or when interrupted by delivery of a
     signal.  Any  change in value of a condition associated with
     the condition variable cannot be inferred by the  return  of
     _lwp_cond_wait()   and   any  such  condition  must  be  re-
     evaluated.

     The   _lwp_cond_timedwait()   function   is    similar    to
     _lwp_cond_wait(), except that the calling LWP will not block
     past the time of day specified by abstime. If  the  time  of
     day  becomes  greater  than  abstime,  _lwp_cond_timedwait()
     returns with the error code ETIME.

     The  _lwp_cond_reltimedwait()   function   is   similar   to
     _lwp_cond_wait(), except that the calling LWP will not block
     past the relative time specified by reltime. If the time  of
     day  becomes greater than the starting time of day plus rel-
     time, _lwp_cond_reltimedwait() returns with the  error  code
     ETIME.

     The     _lwp_cond_wait(),     _lwp_cond_timedwait(),     and
     _lwp_cond_reltimedwait()  functions  always  return with the
     mutex locked and owned by the calling lightweight process.

RETURN VALUES
     Upon successful completion, 0 is returned. A non-zero  value
     indicates an error.





SunOS 5.9           Last change: 13 Apr 2001                    1






System Calls                                    _lwp_cond_wait(2)



ERRORS
     If  any  of   the   following   conditions   are   detected,
     _lwp_cond_wait(),         _lwp_cond_timedwait(),         and
     _lwp_cond_reltimedwait() fail and return  the  corresponding
     value:

     EINVAL
           The cvp argument points to an  invalid  LWP  condition
           variable  or  the mp argument points to an invalid LWP
           mutex.

     EFAULT
           The mp, cvp, or abstime argument points to an  illegal
           address.

     If any of the following conditions occur,  _lwp_cond_wait(),
     _lwp_cond_timedwait(), and _lwp_cond_reltimedwait() fail and
     return the corresponding value:

     EINTR The call was interrupted by a signal or fork(2).

     If    any    of    the    following    conditions     occur,
     _lwp_cond_timedwait()  and _lwp_cond_reltimedwait() fail and
     return the corresponding value:

     ETIME The time specified inabstime or reltime has passed.

EXAMPLES
     Example 1: Use the _lwp_cond_wait() function in a loop test-
     ing some condition.

     The _lwp_cond_wait() function is normally  used  in  a  loop
     testing some condition, as follows:

     lwp_mutex_t m;
     lwp_cond_t cv;
     int cond;
     (void) _lwp_mutex_lock(&m);
     while (cond == FALSE) {
             (void) _lwp_cond_wait(&cv, &m);
     }
     (void) _lwp_mutex_unlock(&m);

     Example 2: Use the _lwp_cond_timedwait() function in a  loop
     testing some condition.

     The _lwp_cond_timedwait() function is also normally used  in
     a  loop  testing some condition. It uses an absolute timeout
     value as follows:

     timestruc_t to;
     lwp_mutex_t m;



SunOS 5.9           Last change: 13 Apr 2001                    2






System Calls                                    _lwp_cond_wait(2)



     lwp_cond_t cv;
     int cond, err;
     (void) _lwp_mutex_lock(&m);
     to.tv_sec = time(NULL) + TIMEOUT;
     to.tv_nsec = 0;
     while (cond == FALSE) {
             err = _lwp_cond_timedwait(&cv, &m, &to);
             if (err == ETIME) {
                     /* timeout, do something */
                     break;
             SENDwhom}
     }
     (void) _lwp_mutex_unlock(&m);

     This example sets a bound on the total wait time even though
     the  _lwp_cond_timedwait()  may  return several times due to
     the condition being signalled or the wait being interrupted.

     Example 3: Use the _lwp_cond_reltimedwait()  function  in  a
     loop testing some condition.

     The _lwp_cond_reltimedwait() function is also normally  used
     in a loop testing some condition. It uses a relative timeout
     value as follows:

     timestruc_t to;
     lwp_mutex_t m;
     lwp_cond_t cv;
     int cond, err;
     (void) _lwp_mutex_lock(&m);
     while (cond == FALSE) {
             to.tv_sec = TIMEOUT;
             to.tv_nsec = 0;
             err = _lwp_cond_reltimedwait(&cv, &m, &to);
             if (err == ETIME) {
                     /* timeout, do something */
                     break;
             }
     }
     (void) _lwp_mutex_unlock(&m);

SEE ALSO
     _lwp_cond_broadcast(2),  _lwp_cond_signal(2),  _lwp_kill(2),
     _lwp_mutex_lock(2), fork(2), kill(2)











SunOS 5.9           Last change: 13 Apr 2001                    3