Ubuntu Manpage: pthread_attr_setscope, pthread_attr_getscope

NAME

       pthread_attr_setscope,  pthread_attr_getscope  -  set/get  contention  scope  attribute in
       thread attributes object

LIBRARY

       POSIX threads library (libpthread, -lpthread)

SYNOPSIS

       #include <pthread.h>

       int pthread_attr_setscope(pthread_attr_t *attr, int scope);
       int pthread_attr_getscope(const pthread_attr_t *restrict attr,
                                 int *restrict scope);

DESCRIPTION

The pthread_attr_setscope() function sets the contention scope attribute of the thread
attributes object referred to by attr to the value specified in scope. The contention
scope attribute defines the set of threads against which a thread competes for resources
such as the CPU. POSIX.1 specifies two possible values for scope:

PTHREAD_SCOPE_SYSTEM
The thread competes for resources with all other threads in all processes on the
system that are in the same scheduling allocation domain (a group of one or more
processors). PTHREAD_SCOPE_SYSTEM threads are scheduled relative to one another
according to their scheduling policy and priority.

PTHREAD_SCOPE_PROCESS
The thread competes for resources with all other threads in the same process that
were also created with the PTHREAD_SCOPE_PROCESS contention scope.
PTHREAD_SCOPE_PROCESS threads are scheduled relative to other threads in the
process according to their scheduling policy and priority. POSIX.1 leaves it
unspecified how these threads contend with other threads in other process on the
system or with other threads in the same process that were created with the
PTHREAD_SCOPE_SYSTEM contention scope.

POSIX.1 requires that an implementation support at least one of these contention scopes.
Linux supports PTHREAD_SCOPE_SYSTEM, but not PTHREAD_SCOPE_PROCESS.

On systems that support multiple contention scopes, then, in order for the parameter
setting made by pthread_attr_setscope() to have effect when calling pthread_create(3), the
caller must use pthread_attr_setinheritsched(3) to set the inherit-scheduler attribute of
the attributes object attr to PTHREAD_EXPLICIT_SCHED.

The pthread_attr_getscope() function returns the contention scope attribute of the thread
attributes object referred to by attr in the buffer pointed to by scope.

RETURN VALUE

       On success, these functions return 0; on error, they return a nonzero error number.

ERRORS

       pthread_attr_setscope() can fail with the following errors:

       EINVAL An invalid value was specified in scope.

       ENOTSUP
              scope specified the value PTHREAD_SCOPE_PROCESS, which is not supported on Linux.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌───────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │Interface                                                      │ Attribute     │ Value   │
       ├───────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │pthread_attr_setscope(), pthread_attr_getscope()               │ Thread safety │ MT-Safe │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       POSIX.1-2001, POSIX.1-2008.

NOTES

       The  PTHREAD_SCOPE_SYSTEM contention scope typically indicates that a user-space thread is
       bound directly to a single kernel-scheduling entity.  This is the case on  Linux  for  the
       obsolete  LinuxThreads  implementation  and the modern NPTL implementation, which are both
       1:1 threading implementations.

       POSIX.1 specifies that the default contention scope is implementation-defined.