1PTHREAD_COND_DESTROY(3P)   POSIX Programmer's Manual  PTHREAD_COND_DESTROY(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
10

NAME

12       pthread_cond_destroy, pthread_cond_init - destroy and initialize condi‐
13       tion variables
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SYNOPSIS

16       #include <pthread.h>
17
18       int pthread_cond_destroy(pthread_cond_t *cond);
19       int pthread_cond_init(pthread_cond_t *restrict cond,
20              const pthread_condattr_t *restrict attr);
21       pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
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23

DESCRIPTION

25       The  pthread_cond_destroy()  function shall destroy the given condition
26       variable specified by cond; the object becomes, in  effect,  uninitial‐
27       ized.  An  implementation  may  cause pthread_cond_destroy() to set the
28       object referenced by cond to an invalid value.  A  destroyed  condition
29       variable  object  can  be  reinitialized using pthread_cond_init(); the
30       results of otherwise referencing the object after it has been destroyed
31       are undefined.
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33       It  shall  be  safe  to  destroy an initialized condition variable upon
34       which no threads are currently blocked. Attempting to destroy a  condi‐
35       tion variable upon which other threads are currently blocked results in
36       undefined behavior.
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38       The pthread_cond_init() function shall initialize the  condition  vari‐
39       able  referenced by cond with attributes referenced by attr. If attr is
40       NULL, the default condition variable  attributes  shall  be  used;  the
41       effect  is the same as passing the address of a default condition vari‐
42       able attributes object. Upon successful initialization,  the  state  of
43       the condition variable shall become initialized.
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45       Only  cond  itself  may  be  used  for performing synchronization.  The
46       result of referring to copies of cond in calls to  pthread_cond_wait(),
47       pthread_cond_timedwait(),   pthread_cond_signal(),  pthread_cond_broad‐
48       cast(), and pthread_cond_destroy() is undefined.
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50       Attempting to initialize  an  already  initialized  condition  variable
51       results in undefined behavior.
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53       In  cases  where default condition variable attributes are appropriate,
54       the macro PTHREAD_COND_INITIALIZER can be used to initialize  condition
55       variables that are statically allocated. The effect shall be equivalent
56       to dynamic initialization by a call to pthread_cond_init() with parame‐
57       ter attr specified as NULL, except that no error checks are performed.
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RETURN VALUE

60       If successful, the pthread_cond_destroy() and pthread_cond_init() func‐
61       tions shall return zero; otherwise, an error number shall  be  returned
62       to indicate the error.
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64       The  [EBUSY] and [EINVAL] error checks, if implemented, shall act as if
65       they were performed immediately at the beginning of processing for  the
66       function and caused an error return prior to modifying the state of the
67       condition variable specified by cond.
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ERRORS

70       The pthread_cond_destroy() function may fail if:
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72       EBUSY  The implementation has detected an attempt to destroy the object
73              referenced  by  cond  while it is referenced (for example, while
74              being used in a pthread_cond_wait() or pthread_cond_timedwait())
75              by another thread.
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77       EINVAL The value specified by cond is invalid.
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80       The pthread_cond_init() function shall fail if:
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82       EAGAIN The system lacked the necessary resources (other than memory) to
83              initialize another condition variable.
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85       ENOMEM Insufficient memory exists to initialize the condition variable.
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87
88       The pthread_cond_init() function may fail if:
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90       EBUSY  The implementation has detected an attempt to  reinitialize  the
91              object referenced by cond, a previously initialized, but not yet
92              destroyed, condition variable.
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94       EINVAL The value specified by attr is invalid.
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97       These functions shall not return an error code of [EINTR].
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99       The following sections are informative.
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EXAMPLES

102       A condition variable can be destroyed immediately after all the threads
103       that  are blocked on it are awakened. For example, consider the follow‐
104       ing code:
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106
107              struct list {
108                  pthread_mutex_t lm;
109                  ...
110              }
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112
113              struct elt {
114                  key k;
115                  int busy;
116                  pthread_cond_t notbusy;
117                  ...
118              }
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120
121              /* Find a list element and reserve it. */
122              struct elt *
123              list_find(struct list *lp, key k)
124              {
125                  struct elt *ep;
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128                  pthread_mutex_lock(&lp->lm);
129                  while ((ep = find_elt(l, k) != NULL) && ep->busy)
130                      pthread_cond_wait(&ep->notbusy, &lp->lm);
131                  if (ep != NULL)
132                      ep->busy = 1;
133                  pthread_mutex_unlock(&lp->lm);
134                  return(ep);
135              }
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137
138              delete_elt(struct list *lp, struct elt *ep)
139              {
140                  pthread_mutex_lock(&lp->lm);
141                  assert(ep->busy);
142                  ... remove ep from list ...
143                  ep->busy = 0;  /* Paranoid. */
144              (A) pthread_cond_broadcast(&ep->notbusy);
145                  pthread_mutex_unlock(&lp->lm);
146              (B) pthread_cond_destroy(&rp->notbusy);
147                  free(ep);
148              }
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150       In this example, the condition variable and its  list  element  may  be
151       freed  (line  B) immediately after all threads waiting for it are awak‐
152       ened (line A), since the mutex and the code ensure that no other thread
153       can touch the element to be deleted.
154

APPLICATION USAGE

156       None.
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RATIONALE

159       See  pthread_mutex_init();  a  similar  rationale  applies to condition
160       variables.
161

FUTURE DIRECTIONS

163       None.
164

SEE ALSO

166       pthread_cond_broadcast(),  pthread_cond_signal(),   pthread_cond_timed‐
167       wait(),   the   Base   Definitions   volume   of  IEEE Std 1003.1-2001,
168       <pthread.h>
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171       Portions of this text are reprinted and reproduced in  electronic  form
172       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
173       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
174       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
175       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
176       event of any discrepancy between this version and the original IEEE and
177       The Open Group Standard, the original IEEE and The Open Group  Standard
178       is  the  referee document. The original Standard can be obtained online
179       at http://www.opengroup.org/unix/online.html .
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183IEEE/The Open Group                  2003             PTHREAD_COND_DESTROY(3P)
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