1PTHREAD_GETCONCURRENCY(3P) POSIX Programmer's ManualPTHREAD_GETCONCURRENCY(3P)
2
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.
10
12 pthread_getconcurrency, pthread_setconcurrency - get and set the level
13 of concurrency
14
16 #include <pthread.h>
17 int pthread_getconcurrency(void);
19 int pthread_setconcurrency(int new_level);
20
23 Unbound threads in a process may or may not be required to be simulta‐
24 neously active. By default, the threads implementation ensures that a
25 sufficient number of threads are active so that the process can con‐
26 tinue to make progress. While this conserves system resources, it may
27 not produce the most effective level of concurrency.
28 The pthread_setconcurrency() function allows an application to inform
30 the threads implementation of its desired concurrency level, new_level.
31 The actual level of concurrency provided by the implementation as a
32 result of this function call is unspecified.
33 If new_level is zero, it causes the implementation to maintain the con‐
35 currency level at its discretion as if pthread_setconcurrency() had
36 never been called.
37 The pthread_getconcurrency() function shall return the value set by a
39 previous call to the pthread_setconcurrency() function. If the
40 pthread_setconcurrency() function was not previously called, this func‐
41 tion shall return zero to indicate that the implementation is maintain‐
42 ing the concurrency level.
43 A call to pthread_setconcurrency() shall inform the implementation of
45 its desired concurrency level. The implementation shall use this as a
46 hint, not a requirement.
47 If an implementation does not support multiplexing of user threads on
49 top of several kernel-scheduled entities, the pthread_setconcurrency()
50 and pthread_getconcurrency() functions are provided for source code
51 compatibility but they shall have no effect when called. To maintain
52 the function semantics, the new_level parameter is saved when
53 pthread_setconcurrency() is called so that a subsequent call to
54 pthread_getconcurrency() shall return the same value.
55
57 If successful, the pthread_setconcurrency() function shall return zero;
58 otherwise, an error number shall be returned to indicate the error.
59 The pthread_getconcurrency() function shall always return the concur‐
61 rency level set by a previous call to pthread_setconcurrency(). If the
62 pthread_setconcurrency() function has never been called, pthread_get‐
63 concurrency() shall return zero.
64
66 The pthread_setconcurrency() function shall fail if:
67 EINVAL The value specified by new_level is negative.
69 EAGAIN The value specific by new_level would cause a system resource to
71 be exceeded.
72 These functions shall not return an error code of [EINTR].
75 The following sections are informative.
77
79 None.
80
82 Use of these functions changes the state of the underlying concurrency
83 upon which the application depends. Library developers are advised to
84 not use the pthread_getconcurrency() and pthread_setconcurrency() func‐
85 tions since their use may conflict with an applications use of these
86 functions.
87
89 None.
90
92 None.
93
95 The Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>
96
98 Portions of this text are reprinted and reproduced in electronic form
99 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
100 -- Portable Operating System Interface (POSIX), The Open Group Base
101 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
102 Electrical and Electronics Engineers, Inc and The Open Group. In the
103 event of any discrepancy between this version and the original IEEE and
104 The Open Group Standard, the original IEEE and The Open Group Standard
105 is the referee document. The original Standard can be obtained online
106 at http://www.opengroup.org/unix/online.html .
107IEEE/The Open Group 2003 PTHREAD_GETCONCURRENCY(3P)