pthread_getconcurrency(3p) — Linux manual page



PROLOG         top

       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         top

       pthread_getconcurrency, pthread_setconcurrency — get and set the
       level of concurrency

SYNOPSIS         top

       #include <pthread.h>

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

DESCRIPTION         top

       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

       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

       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         top

       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         top

       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         top



       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         top



       These functions may be removed in a future version.

SEE ALSO         top

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

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group               2017           PTHREAD_...CURRENCY(3P)

Pages that refer to this page: pthread.h(0p)pthread_setconcurrency(3p)