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pthread_setconcurrency(3) — Linux manual page

pthread_s...ncurrency(3) Library Functions Manualpthread_s...ncurrency(3)

NAME        top

       pthread_setconcurrency, pthread_getconcurrency - set/get the       concurrency level

LIBRARY        top

       POSIX threads library (libpthread,-lpthread)

SYNOPSIS        top

#include <pthread.h>int pthread_setconcurrency(intnew_level);int pthread_getconcurrency(void);

DESCRIPTION        top

       Thepthread_setconcurrency() function informs the implementation       of the application's desired concurrency level, specified innew_level.  The implementation takes this only as a hint: POSIX.1       does not specify the level of concurrency that should be provided       as a result of callingpthread_setconcurrency().       Specifyingnew_level as 0 instructs the implementation to manage       the concurrency level as it deems appropriate.pthread_getconcurrency() returns the current value of the       concurrency level for this process.

RETURN VALUE        top

       On success,pthread_setconcurrency() returns 0; on error, it       returns a nonzero error number.pthread_getconcurrency() always succeeds, returning the       concurrency level set by a previous call topthread_setconcurrency(), or 0, ifpthread_setconcurrency() has       not previously been called.

ERRORS        top

pthread_setconcurrency() can fail with the following error:EINVALnew_level is negative.       POSIX.1 also documents anEAGAINerror ("the value specified bynew_level would cause a system resource to be exceeded").

ATTRIBUTES        top

       For an explanation of the terms used in this section, seeattributes(7).       ┌──────────────────────────────────────┬───────────────┬─────────┐       │Interface│Attribute│Value│       ├──────────────────────────────────────┼───────────────┼─────────┤       │pthread_setconcurrency(),            │ Thread safety │ MT-Safe │       │pthread_getconcurrency()             │               │         │       └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS        top

       POSIX.1-2008.

HISTORY        top

       glibc 2.1.  POSIX.1-2001.

NOTES        top

       The default concurrency level is 0.       Concurrency levels are meaningful only for M:N threading       implementations, where at any moment a subset of a process's set       of user-level threads may be bound to a smaller number of kernel-       scheduling entities.  Setting the concurrency level allows the       application to give the system a hint as to the number of kernel-       scheduling entities that should be provided for efficient       execution of the application.       Both LinuxThreads and NPTL are 1:1 threading implementations, so       setting the concurrency level has no meaning.  In other words, on       Linux these functions merely exist for compatibility with other       systems, and they have no effect on the execution of a program.

SEE ALSO        top

pthread_attr_setscope(3),pthreads(7)

COLOPHON        top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17pthread_s...ncurrency(3)

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