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.\" Copyright (c) 2009 Michael Kerrisk, <mtk.manpages@gmail.com>
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.TH PTHREAD_SETCONCURRENCY 3 2009-04-10 "Linux" "Linux Programmer's Manual"
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pthread_setconcurrency, pthread_getconcurrency \- set/get
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.B #include <pthread.h>
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.BI "int pthread_setconcurrency(int " new_level );
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.BI "int pthread_getconcurrency(void);
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Compile and link with \fI\-pthread\fP.
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.BR pthread_setconcurrency ()
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function informs the implementation of the application's
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desired concurrency level, specified in
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The implementation only takes this as a hint:
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POSIX.1 does not specify the level of concurrency that
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should be provided as a result of calling
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.BR pthread_setconcurrency ().
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as 0 instructs the implementation to manage the concurrency level
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as it deems appropriate.
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.BR pthread_getconcurrency ()
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returns the current value of the concurrency level for this process.
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.BR pthread_setconcurrency ()
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on error, it returns a non-zero error number.
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.BR pthread_getconcurrency ()
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always succeeds, returning the concurrency level set by a previous call to
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.BR pthread_setconcurrency (),
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.BR pthread_setconcurrency ()
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has not previously been called.
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.BR pthread_setconcurrency ()
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can fail with the following error:
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POSIX.1-2001 also documents an
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error ("the value specified by
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would cause a system resource to be exceeded").
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These functions are available in glibc since version 2.1.
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The default concurrency level is 0.
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Concurrency levels are only meaningful for M:N threading implementations,
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where at any moment a subset of a process's set of user-level threads
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may be bound to a smaller number of kernel-scheduling entities.
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Setting the concurrency level allows the application to
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give the system a hint as to the number of kernel-scheduling entities
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that should be provided for efficient execution of the application.
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Both LinuxThreads and NPTL are 1:1 threading implementations,
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so setting the concurrency level has no meaning.
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on Linux these functions merely exist for compatibility with other systems,
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and they have no effect on the execution of a program.
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.BR pthread_attr_setscope (3),
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This page is part of release 3.21 of the Linux
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A description of the project,
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and information about reporting bugs,
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http://www.kernel.org/doc/man-pages/.
added
removed
man3/pthread_setconcurrency.3
