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pthread_setconcurrency(3) [freebsd man page]


pthread_getconcurrency, pthread_setconcurrency -- get or set level of concurrency LIBRARY
POSIX Threads Library (libpthread, -lpthread) SYNOPSIS
#include <pthread.h> int pthread_getconcurrency(void); int pthread_setconcurrency(int new_level); DESCRIPTION
The pthread_setconcurrency() function allows an application to inform the threads implementation of its desired concurrency level, new_level. The actual level of concurrency provided by the implementation as a result of this function call is unspecified. If new_level is zero, it causes the implementation to maintain the concurrency level at its discretion as if pthread_setconcurrency() was never called. The pthread_getconcurrency() function returns the value set by a previous call to the pthread_setconcurrency() function. If the pthread_setconcurrency() function was not previously called, this function returns zero to indicate that the implementation is maintaining the concurrency level. When an application calls pthread_setconcurrency(), it is informing the implementation of its desired concurrency level. The implementation uses this as a hint, not a requirement. RETURN VALUES
If successful, the pthread_setconcurrency() function returns zero. Otherwise, an error number is returned to indicate the error. The pthread_getconcurrency() function always returns the concurrency level set by a previous call to pthread_setconcurrency(). If the pthread_setconcurrency() function has never been called, pthread_getconcurrency() returns zero. ERRORS
The pthread_setconcurrency() function will fail if: [EINVAL] The value specified by new_level is negative. [EAGAIN] The value specified by new_level would cause a system resource to be exceeded. APPLICATION USAGE
Use of these functions changes the state of the underlying concurrency upon which the application depends. Library developers are advised to not use the pthread_getconcurrency() and pthread_setconcurrency() functions since their use may conflict with an application's use of these functions. STANDARDS
The pthread_getconcurrency() and pthread_setconcurrency() functions conform to Version 2 of the Single UNIX Specification (``SUSv2''). BSD
April 11, 2003 BSD

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PTHREAD_SETCONCURRENCY(3)				     Linux Programmer's Manual					 PTHREAD_SETCONCURRENCY(3)

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
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 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at Linux 2009-04-10 PTHREAD_SETCONCURRENCY(3)
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