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 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_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 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 execution of a program.

SEE ALSO

       pthread_attr_setscope(3), pthreads(7)

COLOPHON

       This  page is part of release 3.44 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)