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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 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(), pthread_getconcurrency()                                                                                    │ Thread safety │ MT-Safe │
       └──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

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-schedul‐
       ing 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)

Linux                                                                          2021-03-22                                                      PTHREAD_SETCONCURRENCY(3)