man3/pthread_attr_setscope.3

   1 .\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
   2 .\"     <mtk.manpages@gmail.com>
   3 .\"
   4 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   5 .\"
   6 .TH PTHREAD_ATTR_SETSCOPE 3 2021-03-22 "Linux" "Linux Programmer's Manual"
   7 .SH NAME
   8 pthread_attr_setscope, pthread_attr_getscope \- set/get contention scope
   9 attribute in thread attributes object
  10 .SH SYNOPSIS
  11 .nf
  12 .B #include <pthread.h>
  13 .PP
  14 .BI "int pthread_attr_setscope(pthread_attr_t *" attr ", int " scope );
  15 .BI "int pthread_attr_getscope(const pthread_attr_t *restrict " attr ,
  16 .BI "                          int *restrict " scope );
  17 .PP
  18 Compile and link with \fI\-pthread\fP.
  19 .fi
  20 .SH DESCRIPTION
  21 The
  22 .BR pthread_attr_setscope ()
  23 function sets the contention scope attribute of the
  24 thread attributes object referred to by
  25 .I attr
  26 to the value specified in
  27 .IR scope .
  28 The contention scope attribute defines the set of threads
  29 against which a thread competes for resources such as the CPU.
  30 POSIX.1 specifies two possible values for
  31 .IR scope :
  32 .TP
  33 .B PTHREAD_SCOPE_SYSTEM
  34 The thread competes for resources with all other threads
  35 in all processes on the system that are in the same scheduling
  36 allocation domain (a group of one or more processors).
  37 .B PTHREAD_SCOPE_SYSTEM
  38 threads are scheduled relative to one another
  39 according to their scheduling policy and priority.
  40 .TP
  41 .B PTHREAD_SCOPE_PROCESS
  42 The thread competes for resources with all other threads
  43 in the same process that were also created with the
  44 .BR PTHREAD_SCOPE_PROCESS
  45 contention scope.
  46 .BR PTHREAD_SCOPE_PROCESS
  47 threads are scheduled relative to other threads in the process
  48 according to their scheduling policy and priority.
  49 POSIX.1 leaves it unspecified how these threads contend
  50 with other threads in other process on the system or
  51 with other threads in the same process that
  52 were created with the
  53 .B PTHREAD_SCOPE_SYSTEM
  54 contention scope.
  55 .PP
  56 POSIX.1 requires that an implementation support at least one of these
  57 contention scopes.
  58 Linux supports
  59 .BR PTHREAD_SCOPE_SYSTEM ,
  60 but not
  61 .BR PTHREAD_SCOPE_PROCESS .
  62 .PP
  63 On systems that support multiple contention scopes, then,
  64 in order for the parameter setting made by
  65 .BR pthread_attr_setscope ()
  66 to have effect when calling
  67 .BR pthread_create (3),
  68 the caller must use
  69 .BR pthread_attr_setinheritsched (3)
  70 to set the inherit-scheduler attribute of the attributes object
  71 .I attr
  72 to
  73 .BR PTHREAD_EXPLICIT_SCHED .
  74 .PP
  75 The
  76 .BR pthread_attr_getscope ()
  77 function returns the contention scope attribute of the
  78 thread attributes object referred to by
  79 .I attr
  80 in the buffer pointed to by
  81 .IR scope .
  82 .SH RETURN VALUE
  83 On success, these functions return 0;
  84 on error, they return a nonzero error number.
  85 .SH ERRORS
  86 .BR pthread_attr_setscope ()
  87 can fail with the following errors:
  88 .TP
  89 .B EINVAL
  90 An invalid value was specified in
  91 .IR scope .
  92 .TP
  93 .B ENOTSUP
  94 .IR scope
  95 specified the value
  96 .BR PTHREAD_SCOPE_PROCESS ,
  97 which is not supported on Linux.
  98 .SH ATTRIBUTES
  99 For an explanation of the terms used in this section, see
 100 .BR attributes (7).
 101 .ad l
 102 .nh
 103 .TS
 104 allbox;
 105 lbx lb lb
 106 l l l.
 107 Interface       Attribute       Value
 108 T{
 109 .BR pthread_attr_setscope (),
 110 .BR pthread_attr_getscope ()
 111 T}      Thread safety   MT-Safe
 112 .TE
 113 .hy
 114 .ad
 115 .sp 1
 116 .SH CONFORMING TO
 117 POSIX.1-2001, POSIX.1-2008.
 118 .SH NOTES
 119 The
 120 .B PTHREAD_SCOPE_SYSTEM
 121 contention scope typically indicates that a user-space thread is
 122 bound directly to a single kernel-scheduling entity.
 123 This is the case on Linux for the obsolete LinuxThreads implementation
 124 and the modern NPTL implementation,
 125 which are both 1:1 threading implementations.
 126 .PP
 127 POSIX.1 specifies that the default contention scope is
 128 implementation-defined.
 129 .SH SEE ALSO
 130 .ad l
 131 .nh
 132 .BR pthread_attr_init (3),
 133 .BR pthread_attr_setaffinity_np (3),
 134 .BR pthread_attr_setinheritsched (3),
 135 .BR pthread_attr_setschedparam (3),
 136 .BR pthread_attr_setschedpolicy (3),
 137 .BR pthread_create (3),
 138 .BR pthreads (7)