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PTHREAD_SETCONCURRENCY(3)  Linux Programmer's Manual PTHREAD_SETCONCURRENCY(3)

NAME
       pthread_setconcurrency,	pthread_getconcurrency	-  set/get the concur‐
       rency level

SYNOPSIS
       #include <pthread.h>

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

       Compile and link with -pthread.

DESCRIPTION
       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
       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
       pthread_setconcurrency() can fail with the following error:

       EINVAL new_level is negative.

       POSIX.1-2001  also  documents  an EAGAIN error ("the value specified by
       new_level would cause a system resource to be exceeded").

VERSIONS
       These functions are available in glibc since version 2.1.

CONFORMING TO
       POSIX.1-2001.

NOTES
       The default concurrency level is 0.

       Concurrency levels are meaningful only for  M:N	threading  implementa‐
       tions,  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 set‐
       ting 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
       pthread_attr_setscope(3), pthreads(7)

COLOPHON
       This page is part of release 3.58 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux				  2009-04-10	     PTHREAD_SETCONCURRENCY(3)
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