Ubuntu Manpage: pthread_attr_setscope, pthread_attr_getscope - set/get contention scope attribute in thread attributes

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.1-2008.

HISTORY

       POSIX.1-2001.

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.