PTHREAD_GETCONCURRENCY(3P)                          POSIX Programmer's Manual                         PTHREAD_GETCONCURRENCY(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       pthread_getconcurrency, pthread_setconcurrency - get and set the level of concurrency

SYNOPSIS
       #include <pthread.h>

       int pthread_getconcurrency(void);
       int pthread_setconcurrency(int new_level);


DESCRIPTION
       Unbound  threads in a process may or may not be required to be simultaneously active. By default, the threads implementa-
       tion ensures that a sufficient number of threads are active so that the process can continue to make progress. While this
       conserves system resources, it may not produce the most effective level of concurrency.

       The  pthread_setconcurrency()  function allows an application to inform the threads implementation of its desired concur-
       rency level, new_level. The actual level of concurrency provided by the implementation as a result of this function  call
       is unspecified.

       If new_level is zero, it causes the implementation to maintain the concurrency level at its discretion as if pthread_set-
       concurrency() had never been called.

       The pthread_getconcurrency() function shall return the value set by a previous call to the pthread_setconcurrency() func-
       tion.  If  the  pthread_setconcurrency()  function was not previously called, this function shall return zero to indicate
       that the implementation is maintaining the concurrency level.

       A call to pthread_setconcurrency() shall inform the implementation of its desired concurrency level.  The  implementation
       shall use this as a hint, not a requirement.

       If  an  implementation  does  not  support  multiplexing of user threads on top of several kernel-scheduled entities, the
       pthread_setconcurrency() and pthread_getconcurrency() functions are provided for source code compatibility but they shall
       have  no effect when called. To maintain the function semantics, the new_level parameter is saved when pthread_setconcur-
       rency() is called so that a subsequent call to pthread_getconcurrency() shall return the same value.

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

       The pthread_getconcurrency() function shall always return the concurrency level set by a previous call to pthread_setcon-
       currency(). If the pthread_setconcurrency() function has never been called, pthread_getconcurrency() shall return zero.

ERRORS
       The pthread_setconcurrency() function shall fail if:

       EINVAL The value specified by new_level is negative.

       EAGAIN The value specific by new_level would cause a system resource to be exceeded.


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

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       Use of these functions changes the state of the underlying concurrency upon which the application depends. Library devel-
       opers are advised to not use the pthread_getconcurrency() and pthread_setconcurrency() functions since their use may con-
       flict with an applications use of these functions.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       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, Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                    PTHREAD_GETCONCURRENCY(3P)