pthread_setconcurrency(3) — Linux manual page



NAME         top

       pthread_setconcurrency, pthread_getconcurrency - set/get the
       concurrency level

SYNOPSIS         top

       #include <pthread.h>

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

       Compile and link with -pthread.

DESCRIPTION         top

       The pthread_setconcurrency() function informs the implementation
       of the application's desired concurrency level, specified in
       new_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 calling pthread_setconcurrency().

       Specifying new_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 to
       pthread_setconcurrency(), or 0, if pthread_setconcurrency() has
       not previously been called.

ERRORS         top

       pthread_setconcurrency() can fail with the following error:

       EINVAL new_level is negative.

       POSIX.1 also documents an EAGAIN error ("the value specified by
       new_level would cause a system resource to be exceeded").

VERSIONS         top

       These functions are available in glibc since version 2.1.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface                             Attribute     Value   │
       │pthread_setconcurrency(),             │ Thread safety │ MT-Safe │
       │pthread_getconcurrency()              │               │         │

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008.

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

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Linux                          2021-03-22      PTHREAD_SETCONCURRENCY(3)