man:pthread_getconcurrency
PTHREAD_SETCONCURRENCY(3) Linux Programmer's Manual PTHREAD_SETCONCURRENCY(3)
NAME
pthread_setconcurrency, pthread_getconcurrency - set/get the concur- rency 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).
allbox; lbw25 lb lb l l l. Interface Attribute Value T{ pthread_set- concurrency(), pthread_getconcurrency() T} 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 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
pthread_attr_setscope(3), pthreads(7)
COLOPHON
This page is part of release 4.16 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 PTHREAD_SETCONCURRENCY(3)
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