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



NAME
       pthread_setconcurrency, pthread_getconcurrency - set/get the concurrency 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, speci-
       fied in new_level.  The implementation only takes this 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_setconcur-
       rency(), 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 only meaningful 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 execu-
       tion of a program.

SEE ALSO
       pthread_attr_setscope(3), pthreads(7)

COLOPHON
       This page is part of release 3.25 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)