.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved .TH "PTHREAD_COND_DESTROY" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual" .\" pthread_cond_destroy .SH NAME pthread_cond_destroy, pthread_cond_init \- destroy and initialize condition variables .SH SYNOPSIS .LP \fB#include .br .sp int pthread_cond_destroy(pthread_cond_t *\fP\fIcond\fP\fB); .br int pthread_cond_init(pthread_cond_t *restrict\fP \fIcond\fP\fB, .br \ \ \ \ \ \ const pthread_condattr_t *restrict\fP \fIattr\fP\fB); .br pthread_cond_t\fP \fIcond\fP \fB= PTHREAD_COND_INITIALIZER; \fP \fB .br \fP .SH DESCRIPTION .LP The \fIpthread_cond_destroy\fP() function shall destroy the given condition variable specified by \fIcond\fP; the object becomes, in effect, uninitialized. An implementation may cause \fIpthread_cond_destroy\fP() to set the object referenced by \fIcond\fP to an invalid value. A destroyed condition variable object can be reinitialized using \fIpthread_cond_init\fP(); the results of otherwise referencing the object after it has been destroyed are undefined. .LP 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. .LP The \fIpthread_cond_init\fP() function shall initialize the condition variable referenced by \fIcond\fP with attributes referenced by \fIattr\fP. If \fIattr\fP 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. .LP Only \fIcond\fP itself may be used for performing synchronization. The result of referring to copies of \fIcond\fP in calls to \fIpthread_cond_wait\fP(), \fIpthread_cond_timedwait\fP(), \fIpthread_cond_signal\fP(), \fIpthread_cond_broadcast\fP(), and \fIpthread_cond_destroy\fP() is undefined. .LP Attempting to initialize an already initialized condition variable results in undefined behavior. .LP In cases where default condition variable attributes are appropriate, the macro PTHREAD_COND_INITIALIZER can be used to initialize condition variables that are statically allocated. The effect shall be equivalent to dynamic initialization by a call to \fIpthread_cond_init\fP() with parameter \fIattr\fP specified as NULL, except that no error checks are performed. .SH RETURN VALUE .LP If successful, the \fIpthread_cond_destroy\fP() and \fIpthread_cond_init\fP() functions shall return zero; otherwise, an error number shall be returned to indicate the error. .LP The [EBUSY] and [EINVAL] error checks, if implemented, shall act as if they were performed immediately at the beginning of processing for the function and caused an error return prior to modifying the state of the condition variable specified by \fIcond\fP. .SH ERRORS .LP The \fIpthread_cond_destroy\fP() function may fail if: .TP 7 .B EBUSY The implementation has detected an attempt to destroy the object referenced by \fIcond\fP while it is referenced (for example, while being used in a \fIpthread_cond_wait\fP() or \fIpthread_cond_timedwait\fP()) by another thread. .TP 7 .B EINVAL The value specified by \fIcond\fP is invalid. .sp .LP The \fIpthread_cond_init\fP() function shall fail if: .TP 7 .B EAGAIN The system lacked the necessary resources (other than memory) to initialize another condition variable. .TP 7 .B ENOMEM Insufficient memory exists to initialize the condition variable. .sp .LP The \fIpthread_cond_init\fP() function may fail if: .TP 7 .B EBUSY The implementation has detected an attempt to reinitialize the object referenced by \fIcond\fP, a previously initialized, but not yet destroyed, condition variable. .TP 7 .B EINVAL The value specified by \fIattr\fP is invalid. .sp .LP These functions shall not return an error code of [EINTR]. .LP \fIThe following sections are informative.\fP .SH EXAMPLES .LP 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 .nf \fBstruct list { pthread_mutex_t lm; ... } .sp struct elt { key k; int busy; pthread_cond_t notbusy; ... } .sp /* Find a list element and reserve it. */ struct elt * list_find(struct list *lp, key k) { struct elt *ep; .sp 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); } .sp 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); } \fP .fi .RE .LP 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 .LP None. .SH RATIONALE .LP See \fIpthread_mutex_init\fP() ; a similar rationale applies to condition variables. .SH FUTURE DIRECTIONS .LP None. .SH SEE ALSO .LP \fIpthread_cond_broadcast\fP() , \fIpthread_cond_signal\fP() , \fIpthread_cond_timedwait\fP() , the Base Definitions volume of IEEE\ Std\ 1003.1-2001, \fI\fP .SH COPYRIGHT Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .