Tribblix: manual page: _lwp_cond

_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
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.

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 in abstime 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;
}
}
(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);