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_lwp_cond_wait, _lwp_cond_timedwait, _lwp_cond_reltimedwait - wait on a condition variable

#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);

These functions are used to wait for the occurrence of a condition represented 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 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 reltime, _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.

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

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

EFAULT

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

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

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);

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