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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 5.10 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);
SunOS 5.10 Last change: 13 Apr 2001 2
System Calls _lwp_cond_wait(2)
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);
SunOS 5.10 Last change: 13 Apr 2001 3
System Calls _lwp_cond_wait(2)
SEE ALSO
_lwp_cond_broadcast(2), _lwp_cond_signal(2), _lwp_kill(2),
_lwp_mutex_lock(2), fork(2), kill(2)
SunOS 5.10 Last change: 13 Apr 2001 4
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This page was generated on Wed Sep 12 11:26:53 GMT 2007
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