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, 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  num‐
       ber.

       pthread_getconcurrency()  always succeeds, returning the concurrency level set by a previ‐
       ous 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.

ATTRIBUTES
   Multithreading (see pthreads(7))
       The pthread_setconcurrency() and pthread_getconcurrency() functions are thread-safe.

CONFORMING TO
       POSIX.1-2001.

NOTES
       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 pro‐
       vided 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 compati‐
       bility 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 3.74 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 http://www.kernel.org/doc/man-pages/.



Linux                                       2014-05-23                  PTHREAD_SETCONCURRENCY(3)