pthread_setconcurrency, pthread_getconcurrency - set/get the concurrency level
#include <pthread.h>
int pthread_setconcurrency(int new_level);
int pthread_getconcurrency(void);
Compile and link with -pthread.
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.
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.
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").
These functions are available in glibc since version 2.1.
For an explanation of the terms used in this section, see
attributes(7).
| Interface |
Attribute |
Value |
| pthread_setconcurrency (), pthread_getconcurrency () |
Thread safety |
MT-Safe |
POSIX.1-2001, POSIX.1-2008.
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-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.
pthread_attr_setscope(3),
pthreads(7)