pthread_attr_setscope(3P)pthread_attr_setscope(3P)NAME
pthread_attr_setscope, pthread_attr_getscope - thread scheduling scope
attributes
C SYNOPSIS
#include <pthread.h>
int pthread_attr_setscope(pthread_attr_t *attr, int scope);
int pthread_attr_getscope(const pthread_attr_t *attr, int *oscope);
DESCRIPTION
The pthread_attr_setscope() function sets the thread scheduling scope
attribute in the object attr to the value scope. Possible values for
scope are PTHREAD_SCOPE_SYSTEM, PTHREAD_SCOPE_BOUND_NP and
PTHREAD_SCOPE_PROCESS. The scheduling scope for the attribute object
attr, is returned via the oscope parameter of pthread_attr_getscope().
The default scheduling scope is PTHREAD_SCOPE_PROCESS.
Threads created with system scope have a direct effect on scheduling by
the kernel [see pthread_attr_setschedpolicy() and
pthread_attr_setschedparam()]. System scope threads are therefore
suitable for real-time applications [see realtime]. For example a system
scope thread may run at a higher priority than interrupt threads and
system daemons. Creation of system scope threads requires the
CAP_SCHED_MGT capability [see capability].
Threads created with bound scope are scheduled with respect to the
process in which they are created. Creating bound scope threads does not
require any special capability. Each bound scope thread executes on a
separate kernel execution vehicle. The scheduling policy of these kernel
execution vehicles is determined by the scheduling policy of the process.
These execution vehicles share a single set of kernel scheduling
characteristics. The scheduling attributes of bound scope threads within
the process are controlled by thread-based scheduling attributes [see
pthread_attr_setschedpolicy() and pthread_attr_setschedparam()].
Threads created with process scope are scheduled with respect to the
other process scope pthreads in the process in which they are created
(that is, they are scheduled in user space by the library). Creating
process scope threads does not require any special capability. Although
the scheduling attributes [see pthread_attr_setschedpolicy() and
pthread_attr_setschedparam()] of these threads do not affect scheduling
by the kernel, process scope threads execute on a (usually smaller) pool
of kernel execution vehicles [see pthread_setconcurrency()]. The
scheduling policy of these kernel execution vehicles is determined by the
scheduling policy of the process. These execution vehicles share a single
set of kernel scheduling characteristics.
Scheduling scope makes a big difference to the effect of thread
scheduling, particularly with respect to priority. For example, a
process scope thread with maximum priority merely executes in preference
to other threads within its process. However a thread with the same
Page 1
pthread_attr_setscope(3P)pthread_attr_setscope(3P)
scheduling policy and priority running with system scope runs in
preference to other threads and processes on the machine; such a thread
may run instead of system threads and daemons and seriously affect the
operation of the host.
DIAGNOSTICS
On success pthread_attr_setscope() returns zero; otherwise an error
number is returned:
[EINVAL] The value of scope is not PTHREAD_SCOPE_SYSTEM,
PTHREAD_SCOPE_BOUND_NP or PTHREAD_SCOPE_PROCESS.
[EPERM] The value of scope is PTHREAD_SCOPE_SYSTEM and the process
lacks the CAP_SCHED_MGT capability.
pthread_attr_getscope() always returns zero.
SEE ALSOcapability(4), pthread_attr_init(3P), pthread_attr_setschedparam(3P),
pthread_attr_setschedpolicy(3P), pthread_create(3P),
pthread_setconcurrency(3P), realtime(5), sched_setparam(2),
sched_setscheduler(2).
Page 2
