1PTHREAD_GETCONCURRENCY(P) POSIX Programmer's Manual PTHREAD_GETCONCURRENCY(P)
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6 pthread_getconcurrency, pthread_setconcurrency - get and set the level
7 of concurrency
8
10 #include <pthread.h>
11 int pthread_getconcurrency(void);
13 int pthread_setconcurrency(int new_level);
14
17 Unbound threads in a process may or may not be required to be simulta‐
18 neously active. By default, the threads implementation ensures that a
19 sufficient number of threads are active so that the process can con‐
20 tinue to make progress. While this conserves system resources, it may
21 not produce the most effective level of concurrency.
22 The pthread_setconcurrency() function allows an application to inform
24 the threads implementation of its desired concurrency level, new_level.
25 The actual level of concurrency provided by the implementation as a
26 result of this function call is unspecified.
27 If new_level is zero, it causes the implementation to maintain the con‐
29 currency level at its discretion as if pthread_setconcurrency() had
30 never been called.
31 The pthread_getconcurrency() function shall return the value set by a
33 previous call to the pthread_setconcurrency() function. If the
34 pthread_setconcurrency() function was not previously called, this func‐
35 tion shall return zero to indicate that the implementation is maintain‐
36 ing the concurrency level.
37 A call to pthread_setconcurrency() shall inform the implementation of
39 its desired concurrency level. The implementation shall use this as a
40 hint, not a requirement.
41 If an implementation does not support multiplexing of user threads on
43 top of several kernel-scheduled entities, the pthread_setconcurrency()
44 and pthread_getconcurrency() functions are provided for source code
45 compatibility but they shall have no effect when called. To maintain
46 the function semantics, the new_level parameter is saved when
47 pthread_setconcurrency() is called so that a subsequent call to
48 pthread_getconcurrency() shall return the same value.
49
51 If successful, the pthread_setconcurrency() function shall return zero;
52 otherwise, an error number shall be returned to indicate the error.
53 The pthread_getconcurrency() function shall always return the concur‐
55 rency level set by a previous call to pthread_setconcurrency(). If the
56 pthread_setconcurrency() function has never been called, pthread_get‐
57 concurrency() shall return zero.
58
60 The pthread_setconcurrency() function shall fail if:
61 EINVAL The value specified by new_level is negative.
63 EAGAIN The value specific by new_level would cause a system resource to
65 be exceeded.
66 These functions shall not return an error code of [EINTR].
69 The following sections are informative.
71
73 None.
74
76 Use of these functions changes the state of the underlying concurrency
77 upon which the application depends. Library developers are advised to
78 not use the pthread_getconcurrency() and pthread_setconcurrency() func‐
79 tions since their use may conflict with an applications use of these
80 functions.
81
83 None.
84
86 None.
87
89 The Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>
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92 Portions of this text are reprinted and reproduced in electronic form
93 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
94 -- Portable Operating System Interface (POSIX), The Open Group Base
95 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
96 Electrical and Electronics Engineers, Inc and The Open Group. In the
97 event of any discrepancy between this version and the original IEEE and
98 The Open Group Standard, the original IEEE and The Open Group Standard
99 is the referee document. The original Standard can be obtained online
100 at http://www.opengroup.org/unix/online.html .
101IEEE/The Open Group 2003 PTHREAD_GETCONCURRENCY(P)