NAME         top

       pthread_setconcurrency,  pthread_getconcurrency - set/get the concur‐
       rency 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

       This page is part of release 4.07 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2015-08-08        PTHREAD_SETCONCURRENCY(3)