pthread_attr_setscope, pthread_attr_getscope - set/get contention scope
attribute in thread attributes object
POSIX threads library (
libpthread,
-lpthread)
#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);
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.
On success, these functions return 0; on error, they return a nonzero error
number.
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.
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 |
POSIX.1-2001, POSIX.1-2008.
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.
pthread_attr_init(3),
pthread_attr_setaffinity_np(3),
pthread_attr_setinheritsched(3),
pthread_attr_setschedparam(3),
pthread_attr_setschedpolicy(3),
pthread_create(3),
pthreads(7)