man3/pthread_attr_setscope.3

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