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 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  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

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

       ┌──────────────────────────┬───────────────┬─────────┐
       │Interface                 │ Attribute     │ Value   │
       ├──────────────────────────┼───────────────┼─────────┤
       │pthread_setconcurrency(), │ Thread safety │ MT-Safe │
       │pthread_getconcurrency()  │               │         │
       └──────────────────────────┴───────────────┴─────────┘

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008.

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 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

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