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.

       Only  cond  itself may be used for performing synchronization.  The result of referring to copies of cond
       in     calls      to      pthread_cond_wait(),      pthread_cond_timedwait(),      pthread_cond_signal(),
       pthread_cond_broadcast(), and pthread_cond_destroy() is undefined.

       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  that  are  statically  allocated.  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.

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.

       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 cond.

ERRORS

       The pthread_cond_destroy() function may fail if:

       EBUSY  The  implementation  has  detected an attempt to destroy the object referenced by cond while it is
              referenced (for example, while being used in a pthread_cond_wait() or pthread_cond_timedwait()) by
              another thread.

       EINVAL The value specified by cond is invalid.

       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.

       The pthread_cond_init() function may fail if:

       EBUSY  The  implementation  has  detected  an  attempt  to  reinitialize the object referenced by cond, a
              previously initialized, but not yet destroyed, condition variable.

       EINVAL The value specified by attr is invalid.

       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(&rp->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

       See pthread_mutex_init() ; a similar rationale applies to condition variables.

FUTURE DIRECTIONS

       None.

SEE ALSO

       pthread_cond_broadcast() , pthread_cond_signal() , pthread_cond_timedwait() , the Base Definitions volume
       of IEEE Std 1003.1-2001, <pthread.h>

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 .

IEEE/The Open Group                                   2003                               PTHREAD_COND_DESTROY(P)