pthread_setconcurrency(3) Library Functions Manual pthread_setconcurrency(3)
NAME
pthread_setconcurrency, pthread_getconcurrency - set/get the concur-
rency level
LIBRARY
POSIX threads library (libpthread, -lpthread)
SYNOPSIS
#include <pthread.h>
int pthread_setconcurrency(int new_level);
int pthread_getconcurrency(void);
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 since glibc 2.1.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│pthread_setconcurrency(), │ Thread safety │ MT-Safe │
│pthread_getconcurrency() │ │ │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
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)
Linux man-pages 6.03 2022-12-15 pthread_setconcurrency(3)
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