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 3.24 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/.