NAME

_lwp_cond_wait, _lwp_cond_timedwait - 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);

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 zero before use.

_lwp_cond_wait( ) 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.

_lwp_cond_timedwait( ) 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 then _lwp_cond_timedwait( ) returns with the error code ETIME .

_lwp_cond_wait( ), and_lwp_cond_timedwait( ) always return with the mutex locked and owned by the calling lightweight process.

RETURN VALUES

Zero is returned when successful. A non-zero value indicates an error.

ERRORS

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

EINVAL

cvp points to an invalid LWP condition variable or mp points to an invalid LWP mutex.

EFAULT

mp, cvp, or abstime point to an illegal address.

If any of the following conditions occur, _lwp_cond_wait( ), and _lwp_cond_timedwait( ) 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( ) fails and returns the corresponding value:

ETIME

The time specified in abstime has passed.

EXAMPLES

_lwp_cond_wait() 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);

_lwp_cond_timedwait() 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 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.

SEE ALSO

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