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



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

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
       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__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 specified by new__level would cause a system resource
              to be exceeded.

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

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       Application developers should note that an implementation can always
       ignore any calls to pthread__setconcurrency() and return a constant for
       pthread__getconcurrency().  For this reason, it is not recommended that
       portable applications use this function.

RATIONALE
       None.

FUTURE DIRECTIONS
       These functions may be removed in a future version.

SEE ALSO
       The Base Definitions volume of POSIX.1-2017, <pthread.h>

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_GETCONCURRENCY(3)
