'\" et

.TH PTHREAD_COND_DESTROY "3P" 2013 "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

Only

.IR cond

itself may be used for performing synchronization. The result of

referring to copies of

.IR cond

in calls to

\fIpthread_cond_wait\fR(),

\fIpthread_cond_timedwait\fR(),

\fIpthread_cond_signal\fR(),

\fIpthread_cond_broadcast\fR(),

and

\fIpthread_cond_destroy\fR()

is undefined.

.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

\fB

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(&rp->notbusy);

    free(ep);

}

.fi \fR

.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\(hy2008,

.IR "\fB<pthread.h>\fP"

.SH COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form

from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology

-- Portable Operating System Interface (POSIX), The Open Group Base

Specifications Issue 7, Copyright (C) 2013 by the Institute of

Electrical and Electronics Engineers, Inc and The Open Group.

(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

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 .