pthread_getspecific(3p) — Linux manual page

PTHREAD_GETSPECIFIC(3P) POSIX Programmer's ManualPTHREAD_GETSPECIFIC(3P)

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_getspecific, pthread_setspecific — thread-specific data
       management

SYNOPSIS

       #include <pthread.h>

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

DESCRIPTION

       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 values 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_getspecific() 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_setspecific() 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.

RETURN VALUE

       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.

ERRORS

       No errors are returned from pthread_getspecific().

       The pthread_setspecific() function shall fail if:

       ENOMEM Insufficient memory exists to associate the non-NULL value
              with the key.

       The pthread_setspecific() function shall not return an error code
       of [EINTR].

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       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.

       If an implementation detects that the value specified by the key
       argument to pthread_setspecific() does not refer to a a key value
       obtained from pthread_key_create() or refers to a key that has
       been deleted with pthread_key_delete(), it is recommended that
       the function should fail and report an [EINVAL] error.

FUTURE DIRECTIONS

       None.

SEE ALSO

       pthread_key_create(3p)

       The Base Definitions volume of POSIX.1‐2017, pthread.h(0p)

COPYRIGHT

       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 .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced 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 .

IEEE/The Open Group               2017           PTHREAD_GETSPECIFIC(3P)

Pages that refer to this page: pthread.h(0p), pthread_key_create(3p), pthread_setspecific(3p)

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