_lwp_cond_wait(2) 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 rep‐
resented by an LWP condition variable. LWP condition 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 vari‐
able 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 speci‐
fied 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 spec‐
ified by reltime. If the time of day becomes greater than the starting
time of day plus reltime, _lwp_cond_reltimedwait() returns with the
error code ETIME.
The _lwp_cond_wait(), _lwp_cond_timedwait(), and _lwp_cond_reltimed‐
wait() 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.
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 testing 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;
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 5.10 13 Apr 2001 _lwp_cond_wait(2)
