man3/pthread_attr_setscope.3

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