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pthread_cond_destroy.3p (6738B)

'\" et
.TH PTHREAD_COND_DESTROY "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
pthread_cond_destroy,
pthread_cond_init
\(em destroy and initialize condition variables
.SH SYNOPSIS
.LP
.nf
#include <pthread.h>
.P
int pthread_cond_destroy(pthread_cond_t *\fIcond\fP);
int pthread_cond_init(pthread_cond_t *restrict \fIcond\fP,
    const pthread_condattr_t *restrict \fIattr\fP);
pthread_cond_t \fIcond\fP = PTHREAD_COND_INITIALIZER;
.fi
.SH DESCRIPTION
The
\fIpthread_cond_destroy\fR()
function shall destroy the given condition variable specified by
.IR cond ;
the object becomes, in effect, uninitialized. An implementation may
cause
\fIpthread_cond_destroy\fR()
to set the object referenced by
.IR cond
to an invalid value. A destroyed condition variable object can be
reinitialized using
\fIpthread_cond_init\fR();
the results of otherwise referencing the object after it has been
destroyed are undefined.
.P
It shall be safe to destroy an initialized condition variable upon which
no threads are currently blocked. Attempting to destroy a condition
variable upon which other threads are currently blocked results in
undefined behavior.
.P
The
\fIpthread_cond_init\fR()
function shall initialize the condition variable referenced by
.IR cond
with attributes referenced by
.IR attr .
If
.IR attr
is NULL, the default condition variable attributes shall be used; the
effect is the same as passing the address of a default condition
variable attributes object. Upon successful initialization, the state
of the condition variable shall become initialized.
.P
See
.IR "Section 2.9.9" ", " "Synchronization Object Copies and Alternative Mappings"
for further requirements.
.P
Attempting to initialize an already initialized condition variable
results in undefined behavior.
.P
In cases where default condition variable attributes are appropriate,
the macro PTHREAD_COND_INITIALIZER can be used to initialize condition
variables. The effect shall be equivalent to dynamic initialization by
a call to
\fIpthread_cond_init\fR()
with parameter
.IR attr
specified as NULL, except that no error checks are performed.
.P
The behavior is undefined if the value specified by the
.IR cond
argument to
\fIpthread_cond_destroy\fR()
does not refer to an initialized condition variable.
.P
The behavior is undefined if the value specified by the
.IR attr
argument to
\fIpthread_cond_init\fR()
does not refer to an initialized condition variable attributes object.
.SH "RETURN VALUE"
If successful, the
\fIpthread_cond_destroy\fR()
and
\fIpthread_cond_init\fR()
functions shall return zero; otherwise, an error number shall be
returned to indicate the error.
.SH ERRORS
The
\fIpthread_cond_init\fR()
function shall fail if:
.TP
.BR EAGAIN
The system lacked the necessary resources (other than memory) to
initialize another condition variable.
.TP
.BR ENOMEM
Insufficient memory exists to initialize the condition variable.
.P
These functions shall not return an error code of
.BR [EINTR] .
.LP
.IR "The following sections are informative."
.SH EXAMPLES
A condition variable can be destroyed immediately after all the threads
that are blocked on it are awakened. For example, consider the
following code:
.sp
.RS 4
.nf
struct list {
    pthread_mutex_t lm;
    ...
}
.P
struct elt {
    key k;
    int busy;
    pthread_cond_t notbusy;
    ...
}
.P
/* Find a list element and reserve it. */
struct elt *
list_find(struct list *lp, key k)
{
    struct elt *ep;
.P
    pthread_mutex_lock(&lp->lm);
    while ((ep = find_elt(l, k) != NULL) && ep->busy)
        pthread_cond_wait(&ep->notbusy, &lp->lm);
    if (ep != NULL)
        ep->busy = 1;
    pthread_mutex_unlock(&lp->lm);
    return(ep);
}
.P
delete_elt(struct list *lp, struct elt *ep)
{
    pthread_mutex_lock(&lp->lm);
    assert(ep->busy);
    ... remove ep from list ...
    ep->busy = 0;  /* Paranoid. */
(A) pthread_cond_broadcast(&ep->notbusy);
    pthread_mutex_unlock(&lp->lm);
(B) pthread_cond_destroy(&ep->notbusy);
    free(ep);
}
.fi
.P
.RE
.P
In this example, the condition variable and its list element may be
freed (line B) immediately after all threads waiting for it are
awakened (line A), since the mutex and the code ensure that no other
thread can touch the element to be deleted.
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
If an implementation detects that the value specified by the
.IR cond
argument to
\fIpthread_cond_destroy\fR()
does not refer to an initialized condition variable, it is
recommended that the function should fail and report an
.BR [EINVAL] 
error.
.P
If an implementation detects that the value specified by the
.IR cond
argument to
\fIpthread_cond_destroy\fR()
or
\fIpthread_cond_init\fR()
refers to a condition variable that is in use (for example, in a
\fIpthread_cond_wait\fR()
call) by another thread, or detects that the value specified by the
.IR cond
argument to
\fIpthread_cond_init\fR()
refers to an already initialized condition variable, it is recommended
that the function should fail and report an
.BR [EBUSY] 
error.
.P
If an implementation detects that the value specified by the
.IR attr
argument to
\fIpthread_cond_init\fR()
does not refer to an initialized condition variable attributes object,
it is recommended that the function should fail and report an
.BR [EINVAL] 
error.
.P
See also
.IR "\fIpthread_mutex_destroy\fR\^(\|)".
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIpthread_cond_broadcast\fR\^(\|)",
.IR "\fIpthread_cond_timedwait\fR\^(\|)",
.IR "\fIpthread_mutex_destroy\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<pthread.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .