plucky (3) pthread_cond_destroy.3posix.gz

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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.

NAME

       pthread_cond_destroy, pthread_cond_init — destroy and initialize condition variables

SYNOPSIS

       #include <pthread.h>

       int pthread_cond_destroy(pthread_cond_t *cond);
       int pthread_cond_init(pthread_cond_t *restrict cond,
           const pthread_condattr_t *restrict attr);
       pthread_cond_t cond = PTHREAD_COND_INITIALIZER;

DESCRIPTION

       The  pthread_cond_destroy()  function  shall  destroy the given condition variable specified by cond; the
       object becomes, in effect, uninitialized. An implementation may cause pthread_cond_destroy() to  set  the
       object referenced by cond to an invalid value. A destroyed condition variable object can be reinitialized
       using pthread_cond_init(); the results of otherwise referencing the object after it  has  been  destroyed
       are undefined.

       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.

       The  pthread_cond_init()  function  shall  initialize  the  condition  variable  referenced  by cond with
       attributes referenced by attr.  If 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.

       See Section 2.9.9, Synchronization Object Copies and Alternative Mappings for further requirements.

       Attempting to initialize an already initialized condition variable results in undefined behavior.

       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 pthread_cond_init() with parameter attr specified as NULL, except that no error  checks  are
       performed.

       The  behavior is undefined if the value specified by the cond argument to pthread_cond_destroy() does not
       refer to an initialized condition variable.

       The behavior is undefined if the value specified by the attr argument  to  pthread_cond_init()  does  not
       refer to an initialized condition variable attributes object.

RETURN VALUE

       If successful, the pthread_cond_destroy() and pthread_cond_init() functions shall return zero; otherwise,
       an error number shall be returned to indicate the error.

ERRORS

       The pthread_cond_init() function shall fail if:

       EAGAIN The system lacked the necessary resources (other than  memory)  to  initialize  another  condition
              variable.

       ENOMEM Insufficient memory exists to initialize the condition variable.

       These functions shall not return an error code of [EINTR].

       The following sections are informative.

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:

           struct list {
               pthread_mutex_t lm;
               ...
           }

           struct elt {
               key k;
               int busy;
               pthread_cond_t notbusy;
               ...
           }

           /* Find a list element and reserve it. */
           struct elt *
           list_find(struct list *lp, key k)
           {
               struct elt *ep;

               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);
           }

           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);
           }

       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.

APPLICATION USAGE

       None.

RATIONALE

       If an implementation detects that the value specified by the cond argument to pthread_cond_destroy() does
       not  refer  to  an  initialized  condition  variable, it is recommended that the function should fail and
       report an [EINVAL] error.

       If an implementation detects that the value specified by the cond argument to  pthread_cond_destroy()  or
       pthread_cond_init()  refers to a condition variable that is in use (for example, in a pthread_cond_wait()
       call) by another thread, or detects that the value specified by the cond argument to  pthread_cond_init()
       refers  to an already initialized condition variable, it is recommended that the function should fail and
       report an [EBUSY] error.

       If an implementation detects that the value specified by the attr argument  to  pthread_cond_init()  does
       not  refer  to  an  initialized condition variable attributes object, it is recommended that the function
       should fail and report an [EINVAL] error.

       See also pthread_mutex_destroy().

FUTURE DIRECTIONS

       None.

SEE ALSO

       pthread_cond_broadcast(), pthread_cond_timedwait(), pthread_mutex_destroy()

       The Base Definitions volume of POSIX.1‐2017, <pthread.h>

       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 .

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       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 .