'\" te
.\"  Copyright (c) 2001, Sun Microsystems, Inc.  All Rights Reserved
.TH _lwp_cond_wait 2 "13 Apr 2001" "SunOS 5.11" "System Calls"
.SH NAME
_lwp_cond_wait, _lwp_cond_timedwait, _lwp_cond_reltimedwait \- wait on a condition variable
.SH SYNOPSIS
.LP
.nf
#include <sys/lwp.h>

\fBint\fR \fB_lwp_cond_wait\fR(\fBlwp_cond_t *\fR\fIcvp\fR, \fBlwp_mutex_t *\fR\fImp\fR);
.fi

.LP
.nf
\fBint\fR \fB_lwp_cond_timedwait\fR(\fBlwp_cond_t *\fR\fIcvp\fR, \fBlwp_mutex_t *\fR\fImp\fR,
     \fBtimestruc_t *\fR\fIabstime\fR);
.fi

.LP
.nf
\fBint\fR \fB_lwp_cond_reltimedwait\fR(\fBlwp_cond_t *\fR\fIcvp\fR, \fBlwp_mutex_t *\fR\fImp\fR,
     \fBtimestruc_t *\fR\fIreltime\fR);
.fi

.SH DESCRIPTION
.sp
.LP
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.
.sp
.LP
The \fB_lwp_cond_wait()\fR function atomically releases the LWP mutex pointed to by \fImp\fR and causes the calling LWP to block on the LWP condition variable pointed to by \fIcvp\fR. The blocked LWP may be awakened by \fB_lwp_cond_signal\fR(2), \fB_lwp_cond_broadcast\fR(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 \fB_lwp_cond_wait()\fR and any such condition must be re-evaluated. 
.sp
.LP
The \fB_lwp_cond_timedwait()\fR function is similar to \fB_lwp_cond_wait()\fR, except that the calling LWP will not block past the time of day specified by \fIabstime\fR. If the time of day becomes greater than \fIabstime\fR, \fB_lwp_cond_timedwait()\fR returns with the error code \fBETIME\fR.
.sp
.LP
The \fB_lwp_cond_reltimedwait()\fR function is similar to \fB_lwp_cond_wait()\fR, except that the calling LWP will not block past the relative time specified by \fIreltime\fR. If the time of day becomes greater than the starting time of day plus \fIreltime\fR, \fB_lwp_cond_reltimedwait()\fR returns with the error code \fBETIME\fR.
.sp
.LP
The \fB_lwp_cond_wait()\fR, \fB_lwp_cond_timedwait()\fR, and \fB_lwp_cond_reltimedwait()\fR functions always return with the mutex locked and owned by the calling lightweight process.
.SH RETURN VALUES
.sp
.LP
Upon successful completion, \fB0\fR is returned. A non-zero value indicates an error.
.SH ERRORS
.sp
.LP
If any of the following conditions are detected, \fB_lwp_cond_wait()\fR, \fB_lwp_cond_timedwait()\fR, and \fB_lwp_cond_reltimedwait()\fR fail and return the corresponding value:
.sp
.ne 2
.mk
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 10n
.rt  
The \fIcvp\fR argument points to an invalid LWP condition variable or the \fImp\fR argument points to an invalid LWP mutex.
.RE

.sp
.ne 2
.mk
.na
\fB\fBEFAULT\fR\fR
.ad
.RS 10n
.rt  
The \fImp\fR, \fIcvp\fR, or \fIabstime\fR argument points to an illegal address.
.RE

.sp
.LP
If any of the following conditions occur, \fB_lwp_cond_wait()\fR, \fB_lwp_cond_timedwait()\fR, and \fB_lwp_cond_reltimedwait()\fR fail and return the corresponding value:
.sp
.ne 2
.mk
.na
\fB\fBEINTR\fR\fR
.ad
.RS 9n
.rt  
The call was interrupted by a signal or \fBfork\fR(2).
.RE

.sp
.LP
If any of the following conditions occur, \fB_lwp_cond_timedwait()\fR and \fB_lwp_cond_reltimedwait()\fR fail and return the corresponding value:
.sp
.ne 2
.mk
.na
\fB\fBETIME\fR\fR
.ad
.RS 9n
.rt  
The time specified in\fIabstime\fR or \fIreltime\fR has passed.
.RE

.SH EXAMPLES
.LP
\fBExample 1 \fRUse the \fB_lwp_cond_wait()\fR function in a loop testing some condition.
.sp
.LP
The \fB_lwp_cond_wait()\fR function is normally used in a loop testing some condition, as follows:

.sp
.in +2
.nf
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);
.fi
.in -2

.LP
\fBExample 2 \fRUse the \fB_lwp_cond_timedwait()\fR function in a loop testing some condition.
.sp
.LP
The \fB_lwp_cond_timedwait()\fR function is also normally used in a loop testing some condition. It uses an absolute timeout value as follows:

.sp
.in +2
.nf
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);
.fi
.in -2

.sp
.LP
This example sets a bound on the total wait time even though the \fB_lwp_cond_timedwait()\fR may return several times due to the condition being signalled or the wait being interrupted.

.LP
\fBExample 3 \fRUse the \fB_lwp_cond_reltimedwait()\fR function in a loop testing some condition.
.sp
.LP
The \fB_lwp_cond_reltimedwait()\fR function is also normally used in a loop testing some condition. It uses a relative timeout value as follows:

.sp
.in +2
.nf
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);
.fi
.in -2

.SH SEE ALSO
.sp
.LP
\fB_lwp_cond_broadcast\fR(2), \fB_lwp_cond_signal\fR(2), \fB_lwp_kill\fR(2), \fB_lwp_mutex_lock\fR(2), \fBfork\fR(2), \fBkill\fR(2)