glibc/linuxthreads/man/pthread_attr_init.man

.TH PTHREAD_ATTR_INIT 3 LinuxThreads

.XREF pthread_attr_destroy
.XREF pthread_attr_setdetachstate
.XREF pthread_attr_getdetachstate
.XREF pthread_attr_setschedparam
.XREF pthread_attr_getschedparam
.XREF pthread_attr_setschedpolicy
.XREF pthread_attr_getschedpolicy
.XREF pthread_attr_setinheritsched
.XREF pthread_attr_getinheritsched
.XREF pthread_attr_setscope
.XREF pthread_attr_getscope

.SH NAME
pthread_attr_init, pthread_attr_destroy, pthread_attr_setdetachstate, pthread_attr_getdetachstate, pthread_attr_setschedparam, pthread_attr_getschedparam, pthread_attr_setschedpolicy, pthread_attr_getschedpolicy, pthread_attr_setinheritsched, pthread_attr_getinheritsched, pthread_attr_setscope, pthread_attr_getscope \- thread creation attributes

.SH SYNOPSIS
#include <pthread.h>

int pthread_attr_init(pthread_attr_t *attr);

int pthread_attr_destroy(pthread_attr_t *attr);

int pthread_attr_setdetachstate(pthread_attr_t *attr, int detachstate);

int pthread_attr_getdetachstate(const pthread_attr_t *attr, int *detachstate);

int pthread_attr_setschedpolicy(pthread_attr_t *attr, int policy);

int pthread_attr_getschedpolicy(const pthread_attr_t *attr, int *policy);

int pthread_attr_setschedparam(pthread_attr_t *attr, const struct sched_param *param);

int pthread_attr_getschedparam(const pthread_attr_t *attr, struct sched_param *param);

int pthread_attr_setinheritsched(pthread_attr_t *attr, int inherit);

int pthread_attr_getinheritsched(const pthread_attr_t *attr, int *inherit);

int pthread_attr_setscope(pthread_attr_t *attr, int scope);

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

.SH DESCRIPTION

Setting attributes for threads is achieved by filling a
thread attribute object |attr| of type !pthread_attr_t!, then passing it as
second argument to !pthread_create!(3). Passing !NULL! is equivalent to
passing a thread attribute object with all attributes set to their
default values.

!pthread_attr_init! initializes the thread attribute object |attr| and
fills it with default values for the attributes. (The default values
are listed below for each attribute.)

Each attribute |attrname| (see below for a list of all attributes) can
be individually set using the function !pthread_attr_set!|attrname|
and retrieved using the function !pthread_attr_get!|attrname|.

!pthread_attr_destroy! destroys a thread attribute object, which
must not be reused until it is reinitialized. !pthread_attr_destroy!
does nothing in the LinuxThreads implementation. 

Attribute objects are consulted only when creating a new thread. The
same attribute object can be used for creating several
threads. Modifying an attribute object after a call to
!pthread_create! does not change the attributes of the thread
previously created.

The following thread attributes are supported:

.SS detachstate

Control whether the thread is created in the joinable state (value
!PTHREAD_CREATE_JOINABLE!) or in the detached state
(!PTHREAD_CREATE_DETACHED!). 

Default value: !PTHREAD_CREATE_JOINABLE!.

In the joinable state, another thread can synchronize on the thread
termination and recover its termination code using !pthread_join!(3),
but some of the thread resources are kept allocated after the thread
terminates, and reclaimed only when another thread performs
!pthread_join!(3) on that thread.

In the detached state, the thread resources are immediately freed when
it terminates, but !pthread_join!(3) cannot be used to synchronize on
the thread termination.

A thread created in the joinable state can later be put in the
detached thread using !pthread_detach!(3).

.SS schedpolicy

Select the scheduling policy for the thread: one of
!SCHED_OTHER! (regular, non-realtime scheduling),
!SCHED_RR! (realtime, round-robin) or
!SCHED_FIFO! (realtime, first-in first-out). See
!sched_setpolicy!(2) for more information on scheduling policies.

Default value: !SCHED_OTHER!.

The realtime scheduling policies !SCHED_RR! and !SCHED_FIFO! are
available only to processes with superuser privileges.

The scheduling policy of a thread can be changed after creation with
!pthread_setschedparam!(3).

.SS schedparam

Contain the scheduling parameters (essentially, the scheduling
priority) for the thread. See !sched_setparam!(2) for more information
on scheduling parameters. 

Default value: priority is 0.

This attribute is not significant if the scheduling policy is !SCHED_OTHER!;
it only matters for the realtime policies !SCHED_RR! and !SCHED_FIFO!.

The scheduling priority of a thread can be changed after creation with
!pthread_setschedparam!(3).

.SS inheritsched

Indicate whether the scheduling policy and scheduling parameters for
the newly created thread are determined by the values of the
|schedpolicy| and |schedparam| attributes (value
!PTHREAD_EXPLICIT_SCHED!) or are inherited from the parent thread
(value !PTHREAD_INHERIT_SCHED!).

Default value: !PTHREAD_EXPLICIT_SCHED!.

.SS scope

Define the scheduling contention scope for the created thread.  The
only value supported in the LinuxThreads implementation is
!PTHREAD_SCOPE_SYSTEM!, meaning that the threads contend for CPU time
with all processes running on the machine. In particular, thread
priorities are interpreted relative to the priorities of all other
processes on the machine. The other value specified by the standard,
!PTHREAD_SCOPE_PROCESS!, means that scheduling contention occurs only
between the threads of the running process: thread priorities are
interpreted relative to the priorities of the other threads of the
process, regardless of the priorities of other processes.
!PTHREAD_SCOPE_PROCESS! is not supported in LinuxThreads.

Default value: !PTHREAD_SCOPE_SYSTEM!.

.SH "RETURN VALUE"

All functions return 0 on success and a non-zero error code on error.
On success, the !pthread_attr_get!|attrname| functions also store the
current value of the attribute |attrname| in the location pointed to
by their second argument.

.SH ERRORS

The !pthread_attr_setdetachstate! function returns the following error
codes on error:
.RS
.TP
!EINVAL!
the specified |detachstate| is not one of !PTHREAD_CREATE_JOINABLE! or
!PTHREAD_CREATE_DETACHED!.
.RE

The !pthread_attr_setschedparam! function returns the following error
codes on error:
.RS
.TP
!EINVAL!
the priority specified in |param| is outside the range of allowed
priorities for the scheduling policy currently in |attr|
(1 to 99 for !SCHED_FIFO! and !SCHED_RR!; 0 for !SCHED_OTHER!).
.RE

The !pthread_attr_setschedpolicy! function returns the following error
codes on error:
.RS
.TP
!EINVAL!
the specified |policy| is not one of !SCHED_OTHER!, !SCHED_FIFO!, or
!SCHED_RR!.

.TP
!ENOTSUP!
|policy| is !SCHED_FIFO! or !SCHED_RR!, and the effective user of the
calling process is not super-user.
.RE

The !pthread_attr_setinheritsched! function returns the following error
codes on error:
.RS
.TP
!EINVAL!
the specified |inherit| is not one of !PTHREAD_INHERIT_SCHED! or
!PTHREAD_EXPLICIT_SCHED!.
.RE

The !pthread_attr_setscope! function returns the following error
codes on error:
.RS
.TP
!EINVAL!
the specified |scope| is not one of !PTHREAD_SCOPE_SYSTEM! or
!PTHREAD_SCOPE_PROCESS!.

.TP
!ENOTSUP!
the specified |scope| is !PTHREAD_SCOPE_PROCESS! (not supported).
.RE

.SH AUTHOR
Xavier Leroy <Xavier.Leroy@inria.fr>

.SH "SEE ALSO"
!pthread_create!(3),
!pthread_join!(3),
!pthread_detach!(3),
!pthread_setschedparam!(3).