NAME


pthread_setconcurrency, pthread_getconcurrency - set/get the concurrency level

SYNOPSIS


#include <pthread.h>

int pthread_setconcurrency(int new_level); intpthread_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 non-zero 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 3.23 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/.

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