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 (consult the correspond-
       ing 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 implementation 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  concurrency  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_setconcurrency() had
       never been called.

       The pthread_getconcurrency() function shall return the value set by a previous  call  to  the  pthread_setconcurrency()	function.  If  the
       pthread_setconcurrency()  function  was not previously called, this function shall return zero to indicate that the implementation is main-
       taining 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_setconcur-
       rency() 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_setconcurrency() 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_setconcurrency(). 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 developers are advised
       to not use the pthread_getconcurrency() and pthread_setconcurrency() functions since their use may conflict 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 Technol-
       ogy -- 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_GETCONCURRENCY(3P)