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

NAME
       pthreadsetconcurrency,  pthreadgetconcurrency  -  set/get the concur‐
       rency level

SYNOPSIS
       #include 

       int pthreadsetconcurrency(int newlevel);
       int pthreadgetconcurrency(void);

       Compile and link with -pthread.

DESCRIPTION
       The pthreadsetconcurrency() function informs the implementation of the
       application's  desired  concurrency level, specified in newlevel.  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
       pthreadsetconcurrency().

       Specifying newlevel as 0 instructs the implementation  to  manage  the
       concurrency level as it deems appropriate.

       pthreadgetconcurrency()  returns  the current value of the concurrency
       level for this process.

RETURN VALUE
       On success, pthreadsetconcurrency() returns 0; on error, it returns  a
       nonzero error number.

       pthreadgetconcurrency()  always  succeeds,  returning  the concurrency
       level set by a previous call  to  pthreadsetconcurrency(),  or  0,  if
       pthreadsetconcurrency() has not previously been called.

ERRORS
       pthreadsetconcurrency() can fail with the following error:

       EINVAL newlevel is negative.

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

VERSIONS
       These functions are available in glibc since version 2.1.

ATTRIBUTES
       For  an  explanation  of  the  terms  used   in   this   section,   see
       attributes(7).

       ┌──────────────────────────┬───────────────┬─────────┐
       │Interface                 │ Attribute     │ Value   │
       ├──────────────────────────┼───────────────┼─────────┤
       │pthreadsetconcurrency(), │ Thread safety │ MT-Safe │
       │pthreadgetconcurrency()  │               │         │
       └──────────────────────────┴───────────────┴─────────┘
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
       pthreadattrsetscope(3), pthreads(7)

COLOPHON
       This page is part of release 3.53 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         PTHREADSETCONCURRENCY(3)