pthread_getspecific manpage

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       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.

       pthread_getspecific, pthread_setspecific - thread-specific data manage-

       #include <pthread.h>

       void *pthread_getspecific(pthread_key_t key);
       int pthread_setspecific(pthread_key_t key, const void *value);

       The  pthread_getspecific()  function  shall  return the value currently
       bound to the specified key on behalf of the calling thread.

       The pthread_setspecific() function shall	 associate  a  thread-specific
       value  with a key obtained via a previous call to pthread_key_create().
       Different threads may bind different values to the same key. These val-
       ues  are	 typically  pointers to blocks of dynamically allocated memory
       that have been reserved for use by the calling thread.

       The effect of calling  pthread_getspecific()  or	 pthread_setspecific()
       with  a	key  value not obtained from pthread_key_create() or after key
       has been deleted with pthread_key_delete() is undefined.

       Both pthread_getspecific() and pthread_setspecific() may be called from
       a  thread-specific  data destructor function. A call to pthread_getspe-
       cific() for the thread-specific data key being destroyed	 shall	return
       the  value  NULL,  unless  the  value  is changed (after the destructor
       starts) by a call  to  pthread_setspecific().  Calling  pthread_setspe-
       cific()	from  a	 thread-specific  data	destructor  routine may result
       either in lost storage (after  at  least	 PTHREAD_DESTRUCTOR_ITERATIONS
       attempts at destruction) or in an infinite loop.

       Both functions may be implemented as macros.

       The  pthread_getspecific()  function  shall  return the thread-specific
       data value associated with the given key. If  no	 thread-specific  data
       value is associated with key, then the value NULL shall be returned.

       If  successful,	the  pthread_setspecific() function shall return zero;
       otherwise, an error number shall be returned to indicate the error.

       No errors are returned from pthread_getspecific().

       The pthread_setspecific() function shall fail if:

       ENOMEM Insufficient memory exists to associate the value with the  key.

       The pthread_setspecific() function may fail if:

       EINVAL The key value is invalid.

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

       The following sections are informative.



       Performance  and	 ease-of-use of pthread_getspecific() are critical for
       functions that rely on maintaining state in thread-specific data. Since
       no  errors  are required to be detected by it, and since the only error
       that could be detected is the use of an invalid key,  the  function  to
       pthread_getspecific()  has  been designed to favor speed and simplicity
       over error reporting.


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

       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_GETSPECIFIC(P)
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