1PTHREAD_GETCONCURRENCY(3P) POSIX Programmer's ManualPTHREAD_GETCONCURRENCY(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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NAME

12       pthread_getconcurrency, pthread_setconcurrency — get and set the  level
13       of concurrency
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SYNOPSIS

16       #include <pthread.h>
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18       int pthread_getconcurrency(void);
19       int pthread_setconcurrency(int new_level);
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DESCRIPTION

22       Unbound  threads in a process may or may not be required to be simulta‐
23       neously active. By default, the threads implementation ensures  that  a
24       sufficient  number  of  threads are active so that the process can con‐
25       tinue to make progress. While this conserves system resources,  it  may
26       not produce the most effective level of concurrency.
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28       The  pthread_setconcurrency()  function allows an application to inform
29       the threads implementation of its desired concurrency level, new_level.
30       The  actual  level  of  concurrency provided by the implementation as a
31       result of this function call is unspecified.
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33       If new_level is zero, it causes the implementation to maintain the con‐
34       currency  level  at  its  discretion as if pthread_setconcurrency() had
35       never been called.
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37       The pthread_getconcurrency() function shall return the value set  by  a
38       previous   call   to  the  pthread_setconcurrency()  function.  If  the
39       pthread_setconcurrency() function was not previously called, this func‐
40       tion shall return zero to indicate that the implementation is maintain‐
41       ing the concurrency level.
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43       A call to pthread_setconcurrency() shall inform the  implementation  of
44       its  desired concurrency level.  The implementation shall use this as a
45       hint, not a requirement.
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47       If an implementation does not support multiplexing of user  threads  on
48       top  of several kernel-scheduled entities, the pthread_setconcurrency()
49       and pthread_getconcurrency() functions are  provided  for  source  code
50       compatibility  but  they  shall have no effect when called. To maintain
51       the  function  semantics,  the  new_level  parameter  is   saved   when
52       pthread_setconcurrency()  is  called  so  that  a  subsequent  call  to
53       pthread_getconcurrency() shall return the same value.
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RETURN VALUE

56       If successful, the pthread_setconcurrency() function shall return zero;
57       otherwise, an error number shall be returned to indicate the error.
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59       The  pthread_getconcurrency()  function shall always return the concur‐
60       rency level set by a previous call to pthread_setconcurrency().  If the
61       pthread_setconcurrency()  function  has never been called, pthread_get‐
62       concurrency() shall return zero.
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ERRORS

65       The pthread_setconcurrency() function shall fail if:
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67       EINVAL The value specified by new_level is negative.
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69       EAGAIN The value specified by new_level would cause a  system  resource
70              to be exceeded.
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72       The pthread_setconcurrency() function shall not return an error code of
73       [EINTR].
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75       The following sections are informative.
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EXAMPLES

78       None.
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APPLICATION USAGE

81       Application developers should note that an  implementation  can  always
82       ignore  any calls to pthread_setconcurrency() and return a constant for
83       pthread_getconcurrency().  For this reason, it is not recommended  that
84       portable applications use this function.
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RATIONALE

87       None.
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FUTURE DIRECTIONS

90       These functions may be removed in a future version.
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SEE ALSO

93       The Base Definitions volume of POSIX.1‐2017, <pthread.h>
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96       Portions  of  this text are reprinted and reproduced in electronic form
97       from IEEE Std 1003.1-2017, Standard for Information Technology --  Por‐
98       table  Operating System Interface (POSIX), The Open Group Base Specifi‐
99       cations Issue 7, 2018 Edition, Copyright (C) 2018 by the  Institute  of
100       Electrical  and  Electronics Engineers, Inc and The Open Group.  In the
101       event of any discrepancy between this version and the original IEEE and
102       The  Open Group Standard, the original IEEE and The Open Group Standard
103       is the referee document. The original Standard can be  obtained  online
104       at http://www.opengroup.org/unix/online.html .
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106       Any  typographical  or  formatting  errors that appear in this page are
107       most likely to have been introduced during the conversion of the source
108       files  to  man page format. To report such errors, see https://www.ker
109       nel.org/doc/man-pages/reporting_bugs.html .
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113IEEE/The Open Group                  2017           PTHREAD_GETCONCURRENCY(3P)
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