source: rtems-docs/posix_users/thread.rst @ 1264a8f

Thread Manager
##############

Introduction
============

The thread manager implements the functionality required of the thread
manager as defined by POSIX 1003.1b. This standard requires that
a compliant operating system provide the facilties to manage multiple
threads of control and defines the API that must be provided.

The services provided by the thread manager are:

- ``pthread_attr_init`` - Initialize a Thread Attribute Set

- ``pthread_attr_destroy`` - Destroy a Thread Attribute Set

- ``pthread_attr_setdetachstate`` - Set Detach State

- ``pthread_attr_getdetachstate`` - Get Detach State

- ``pthread_attr_setstacksize`` - Set Thread Stack Size

- ``pthread_attr_getstacksize`` - Get Thread Stack Size

- ``pthread_attr_setstackaddr`` - Set Thread Stack Address

- ``pthread_attr_getstackaddr`` - Get Thread Stack Address

- ``pthread_attr_setscope`` - Set Thread Scheduling Scope

- ``pthread_attr_getscope`` - Get Thread Scheduling Scope

- ``pthread_attr_setinheritsched`` - Set Inherit Scheduler Flag

- ``pthread_attr_getinheritsched`` - Get Inherit Scheduler Flag

- ``pthread_attr_setschedpolicy`` - Set Scheduling Policy

- ``pthread_attr_getschedpolicy`` - Get Scheduling Policy

- ``pthread_attr_setschedparam`` - Set Scheduling Parameters

- ``pthread_attr_getschedparam`` - Get Scheduling Parameters

- ``pthread_attr_getaffinity_np`` - Get Thread Affinity Attribute

- ``pthread_attr_setaffinity_np`` - Set Thread Affinity Attribute

- ``pthread_create`` - Create a Thread

- ``pthread_exit`` - Terminate the Current Thread

- ``pthread_detach`` - Detach a Thread

- ``pthread_getattr_np`` - Get Thread Attributes

- ``pthread_join`` - Wait for Thread Termination

- ``pthread_self`` - Get Thread ID

- ``pthread_equal`` - Compare Thread IDs

- ``pthread_once`` - Dynamic Package Initialization

- ``pthread_setschedparam`` - Set Thread Scheduling Parameters

- ``pthread_getschedparam`` - Get Thread Scheduling Parameters

- ``pthread_getaffinity_np`` - Get Thread Affinity

- ``pthread_setaffinity_np`` - Set Thread Affinity

Background
==========

Thread Attributes
-----------------

Thread attributes are utilized only at thread creation time. A thread
attribute structure may be initialized and passed as an argument to
the ``pthread_create`` routine.

*stack address*
    is the address of the optionally user specified stack area for this thread.
    If this value is NULL, then RTEMS allocates the memory for the thread stack
    from the RTEMS Workspace Area. Otherwise, this is the user specified
    address for the memory to be used for the thread’s stack. Each thread must
    have a distinct stack area. Each processor family has different alignment
    rules which should be followed.

*stack size*
    is the minimum desired size for this thread’s stack area.
    If the size of this area as specified by the stack size attribute
    is smaller than the minimum for this processor family and the stack
    is not user specified, then RTEMS will automatically allocate a
    stack of the minimum size for this processor family.

*contention scope*
    specifies the scheduling contention scope. RTEMS only supports the
    PTHREAD_SCOPE_PROCESS scheduling contention scope.

*scheduling inheritance*
    specifies whether a user specified or the scheduling policy and
    parameters of the currently executing thread are to be used. When
    this is PTHREAD_INHERIT_SCHED, then the scheduling policy and
    parameters of the currently executing thread are inherited by
    the newly created thread.

*scheduling policy and parameters*
    specify the manner in which the thread will contend for the processor.
    The scheduling parameters are interpreted based on the specified policy.
    All policies utilize the thread priority parameter.

Operations
==========

There is currently no text in this section.

Services
========

This section details the thread manager’s services.
A subsection is dedicated to each of this manager’s services
and describes the calling sequence, related constants, usage,
and status codes.

pthread_attr_init - Initialize a Thread Attribute Set
-----------------------------------------------------
.. index:: pthread_attr_init
.. index:: initialize a thread attribute set

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_init(
    pthread_attr_t \*attr
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

**DESCRIPTION:**

The ``pthread_attr_init`` routine initializes the thread attributes
object specified by ``attr`` with the default value for all of the
individual attributes.

**NOTES:**

The settings in the default attributes are implementation defined. For
RTEMS, the default attributes are as follows:

- stackadr
  is not set to indicate that RTEMS is to allocate the stack memory.

- stacksize
  is set to ``PTHREAD_MINIMUM_STACK_SIZE``.

- contentionscope
  is set to ``PTHREAD_SCOPE_PROCESS``.

- inheritsched
  is set to ``PTHREAD_INHERIT_SCHED`` to indicate that the created
  thread inherits its scheduling attributes from its parent.

- detachstate
  is set to ``PTHREAD_CREATE_JOINABLE``.

pthread_attr_destroy - Destroy a Thread Attribute Set
-----------------------------------------------------
.. index:: pthread_attr_destroy
.. index:: destroy a thread attribute set

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_destroy(
    pthread_attr_t \*attr
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

**DESCRIPTION:**

The ``pthread_attr_destroy`` routine is used to destroy a thread
attributes object. The behavior of using an attributes object after
it is destroyed is implementation dependent.

**NOTES:**

NONE

pthread_attr_setdetachstate - Set Detach State
----------------------------------------------
.. index:: pthread_attr_setdetachstate
.. index:: set detach state

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_setdetachstate(
    pthread_attr_t \*attr,
    int             detachstate
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The detachstate argument is invalid.

**DESCRIPTION:**

The ``pthread_attr_setdetachstate`` routine is used to value of the``detachstate`` attribute. This attribute controls whether the
thread is created in a detached state.

The ``detachstate`` can be either ``PTHREAD_CREATE_DETACHED`` or``PTHREAD_CREATE_JOINABLE``. The default value for all threads is``PTHREAD_CREATE_JOINABLE``.

**NOTES:**

If a thread is in a detached state,
then the use of the ID with the ``pthread_detach`` or``pthread_join`` routines is an error.

pthread_attr_getdetachstate - Get Detach State
----------------------------------------------
.. index:: pthread_attr_getdetachstate
.. index:: get detach state

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_getdetachstate(
    const pthread_attr_t \*attr,
    int                  \*detachstate
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The detatchstate pointer argument is invalid.

**DESCRIPTION:**

The ``pthread_attr_getdetachstate`` routine is used to obtain the
current value of the ``detachstate`` attribute as specified
by the ``attr`` thread attribute object.

**NOTES:**

NONE

pthread_attr_setstacksize - Set Thread Stack Size
-------------------------------------------------
.. index:: pthread_attr_setstacksize
.. index:: set thread stack size

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_setstacksize(
    pthread_attr_t \*attr,
    size_t          stacksize
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

**DESCRIPTION:**

The ``pthread_attr_setstacksize`` routine is used to set the``stacksize`` attribute in the ``attr`` thread attribute
object.

**NOTES:**

As required by POSIX, RTEMS defines the feature symbol``_POSIX_THREAD_ATTR_STACKSIZE`` to indicate that this
routine is supported.

If the specified stacksize is below the minimum required for this CPU
(``PTHREAD_STACK_MIN``, then the stacksize will be set to the minimum
for this CPU.

pthread_attr_getstacksize - Get Thread Stack Size
-------------------------------------------------
.. index:: pthread_attr_getstacksize
.. index:: get thread stack size

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_getstacksize(
    const pthread_attr_t \*attr,
    size_t               \*stacksize
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The stacksize pointer argument is invalid.

**DESCRIPTION:**

The ``pthread_attr_getstacksize`` routine is used to obtain the``stacksize`` attribute in the ``attr`` thread attribute
object.

**NOTES:**

As required by POSIX, RTEMS defines the feature symbol``_POSIX_THREAD_ATTR_STACKSIZE`` to indicate that this
routine is supported.

pthread_attr_setstackaddr - Set Thread Stack Address
----------------------------------------------------
.. index:: pthread_attr_setstackaddr
.. index:: set thread stack address

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_setstackaddr(
    pthread_attr_t \*attr,
    void           \*stackaddr
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

**DESCRIPTION:**

The ``pthread_attr_setstackaddr`` routine is used to set the``stackaddr`` attribute in the ``attr`` thread attribute
object.

**NOTES:**

As required by POSIX, RTEMS defines the feature symbol``_POSIX_THREAD_ATTR_STACKADDR`` to indicate that this
routine is supported.

It is imperative to the proper operation of the system that
each thread have sufficient stack space.

pthread_attr_getstackaddr - Get Thread Stack Address
----------------------------------------------------
.. index:: pthread_attr_getstackaddr
.. index:: get thread stack address

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_getstackaddr(
    const pthread_attr_t  \*attr,
    void                 \**stackaddr
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The stackaddr pointer argument is invalid.

**DESCRIPTION:**

The ``pthread_attr_getstackaddr`` routine is used to obtain the``stackaddr`` attribute in the ``attr`` thread attribute
object.

**NOTES:**

As required by POSIX, RTEMS defines the feature symbol``_POSIX_THREAD_ATTR_STACKADDR`` to indicate that this
routine is supported.

pthread_attr_setscope - Set Thread Scheduling Scope
---------------------------------------------------
.. index:: pthread_attr_setscope
.. index:: set thread scheduling scope

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_setscope(
    pthread_attr_t \*attr,
    int             contentionscope
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The contention scope specified is not valid.

*ENOTSUP*
    The contention scope specified (PTHREAD_SCOPE_SYSTEM) is not supported.

**DESCRIPTION:**

The ``pthread_attr_setscope`` routine is used to set the contention
scope field in the thread attribute object ``attr`` to the value
specified by ``contentionscope``.

The ``contentionscope`` must be either ``PTHREAD_SCOPE_SYSTEM``
to indicate that the thread is to be within system scheduling contention
or ``PTHREAD_SCOPE_PROCESS`` indicating that the thread is to be
within the process scheduling contention scope.

**NOTES:**

As required by POSIX, RTEMS defines the feature symbol``_POSIX_THREAD_PRIORITY_SCHEDULING`` to indicate that the
family of routines to which this routine belongs is supported.

pthread_attr_getscope - Get Thread Scheduling Scope
---------------------------------------------------
.. index:: pthread_attr_getscope
.. index:: get thread scheduling scope

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_getscope(
    const pthread_attr_t \*attr,
    int                  \*contentionscope
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The contentionscope pointer argument is invalid.

**DESCRIPTION:**

The ``pthread_attr_getscope`` routine is used to obtain the
value of the contention scope field in the thread attributes
object ``attr``. The current value is returned in``contentionscope``.

**NOTES:**

As required by POSIX, RTEMS defines the feature symbol``_POSIX_THREAD_PRIORITY_SCHEDULING`` to indicate that the
family of routines to which this routine belongs is supported.

pthread_attr_setinheritsched - Set Inherit Scheduler Flag
---------------------------------------------------------
.. index:: pthread_attr_setinheritsched
.. index:: set inherit scheduler flag

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_setinheritsched(
    pthread_attr_t \*attr,
    int             inheritsched
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The specified scheduler inheritance argument is invalid.

**DESCRIPTION:**

The ``pthread_attr_setinheritsched`` routine is used to set the
inherit scheduler field in the thread attribute object ``attr`` to
the value specified by ``inheritsched``.

The ``contentionscope`` must be either ``PTHREAD_INHERIT_SCHED``
to indicate that the thread is to inherit the scheduling policy
and parameters fromthe creating thread, or ``PTHREAD_EXPLICIT_SCHED``
to indicate that the scheduling policy and parameters for this thread
are to be set from the corresponding values in the attributes object.
If ``contentionscope`` is ``PTHREAD_INHERIT_SCHED``, then the
scheduling attributes in the ``attr`` structure will be ignored
at thread creation time.

**NOTES:**

As required by POSIX, RTEMS defines the feature symbol``_POSIX_THREAD_PRIORITY_SCHEDULING`` to indicate that the
family of routines to which this routine belongs is supported.

pthread_attr_getinheritsched - Get Inherit Scheduler Flag
---------------------------------------------------------
.. index:: pthread_attr_getinheritsched
.. index:: get inherit scheduler flag

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_getinheritsched(
    const pthread_attr_t \*attr,
    int                  \*inheritsched
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The inheritsched pointer argument is invalid.

**DESCRIPTION:**

The ``pthread_attr_getinheritsched`` routine is used to
object the current value of the inherit scheduler field in
the thread attribute object ``attr``.

**NOTES:**

As required by POSIX, RTEMS defines the feature symbol``_POSIX_THREAD_PRIORITY_SCHEDULING`` to indicate that the
family of routines to which this routine belongs is supported.

pthread_attr_setschedpolicy - Set Scheduling Policy
---------------------------------------------------
.. index:: pthread_attr_setschedpolicy
.. index:: set scheduling policy

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_setschedpolicy(
    pthread_attr_t \*attr,
    int             policy
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*ENOTSUP*
    The specified scheduler policy argument is invalid.

**DESCRIPTION:**

The ``pthread_attr_setschedpolicy`` routine is used to set the
scheduler policy field in the thread attribute object ``attr`` to
the value specified by ``policy``.

Scheduling policies may be one of the following:

- ``SCHED_DEFAULT``

- ``SCHED_FIFO``

- ``SCHED_RR``

- ``SCHED_SPORADIC``

- ``SCHED_OTHER``

The precise meaning of each of these is discussed elsewhere in this
manual.

**NOTES:**

As required by POSIX, RTEMS defines the feature symbol``_POSIX_THREAD_PRIORITY_SCHEDULING`` to indicate that the
family of routines to which this routine belongs is supported.

pthread_attr_getschedpolicy - Get Scheduling Policy
---------------------------------------------------
.. index:: pthread_attr_getschedpolicy
.. index:: get scheduling policy

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_getschedpolicy(
    const pthread_attr_t \*attr,
    int                  \*policy
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The specified scheduler policy argument pointer is invalid.

**DESCRIPTION:**

The ``pthread_attr_getschedpolicy`` routine is used to obtain the
scheduler policy field from the thread attribute object ``attr``.
The value of this field is returned in ``policy``.

**NOTES:**

As required by POSIX, RTEMS defines the feature symbol``_POSIX_THREAD_PRIORITY_SCHEDULING`` to indicate that the
family of routines to which this routine belongs is supported.

pthread_attr_setschedparam - Set Scheduling Parameters
------------------------------------------------------
.. index:: pthread_attr_setschedparam
.. index:: set scheduling parameters

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_setschedparam(
    pthread_attr_t           \*attr,
    const struct sched_param  param
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The specified scheduler parameter argument is invalid.

**DESCRIPTION:**

The ``pthread_attr_setschedparam`` routine is used to set the
scheduler parameters field in the thread attribute object ``attr`` to
the value specified by ``param``.

**NOTES:**

As required by POSIX, RTEMS defines the feature symbol``_POSIX_THREAD_PRIORITY_SCHEDULING`` to indicate that the
family of routines to which this routine belongs is supported.

pthread_attr_getschedparam - Get Scheduling Parameters
------------------------------------------------------
.. index:: pthread_attr_getschedparam
.. index:: get scheduling parameters

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_attr_getschedparam(
    const pthread_attr_t \*attr,
    struct sched_param   \*param
    );

**STATUS CODES:**

*EINVAL*
    The attribute pointer argument is invalid.

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The specified scheduler parameter argument pointer is invalid.

**DESCRIPTION:**

The ``pthread_attr_getschedparam`` routine is used to obtain the
scheduler parameters field from the thread attribute object ``attr``.
The value of this field is returned in ``param``.

**NOTES:**

As required by POSIX, RTEMS defines the feature symbol``_POSIX_THREAD_PRIORITY_SCHEDULING`` to indicate that the
family of routines to which this routine belongs is supported.

pthread_attr_getaffinity_np - Get Thread Affinity Attribute
-----------------------------------------------------------

**CALLING SEQUENCE:**

.. code:: c

    #define _GNU_SOURCE
    #include <pthread.h>
    int pthread_attr_getaffinity_np(
    const pthread_attr_t \*attr,
    size_t                cpusetsize,
    cpu_set_t            \*cpuset
    );

**STATUS CODES:**

*EFAULT*
    The attribute pointer argument is invalid.

*EFAULT*
    The cpuset pointer argument is invalid.

*EINVAL*
    The ``cpusetsize`` does not match the value of ``affinitysetsize``
    field in the thread attribute object.

**DESCRIPTION:**

The ``pthread_attr_getaffinity_np`` routine is used to obtain the``affinityset`` field from the thread attribute object ``attr``.
The value of this field is returned in ``cpuset``.

**NOTES:**

NONE

pthread_attr_setaffinity_np - Set Thread Affinity Attribute
-----------------------------------------------------------

**CALLING SEQUENCE:**

.. code:: c

    #define _GNU_SOURCE
    #include <pthread.h>
    int pthread_attr_setaffinity_np(
    pthread_attr_t    \*attr,
    size_t             cpusetsize,
    const cpu_set_t   \*cpuset
    );

**STATUS CODES:**

*EFAULT*
    The attribute pointer argument is invalid.

*EFAULT*
    The cpuset pointer argument is invalid.

*EINVAL*
    The ``cpusetsize`` does not match the value of ``affinitysetsize``
    field in the thread attribute object.

*EINVAL*
    The ``cpuset`` did not select a valid cpu.

*EINVAL*
    The ``cpuset`` selected a cpu that was invalid.

**DESCRIPTION:**

The ``pthread_attr_setaffinity_np`` routine is used to set the``affinityset`` field in the thread attribute object ``attr``.
The value of this field is returned in ``cpuset``.

**NOTES:**

NONE

pthread_create - Create a Thread
--------------------------------
.. index:: pthread_create
.. index:: create a thread

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_create(
    pthread_t             \*thread,
    const pthread_attr_t  \*attr,
    void                 (\*start_routine)( void \*),
    void                  \*arg
    );

**STATUS CODES:**

*EINVAL*
    The attribute set is not initialized.

*EINVAL*
    The user specified a stack address and the size of the area was not
    large enough to meet this processor’s minimum stack requirements.

*EINVAL*
    The specified scheduler inheritance policy was invalid.

*ENOTSUP*
    The specified contention scope was PTHREAD_SCOPE_PROCESS.

*EINVAL*
    The specified thread priority was invalid.

*EINVAL*
    The specified scheduling policy was invalid.

*EINVAL*
    The scheduling policy was SCHED_SPORADIC and the specified replenishment
    period is less than the initial budget.

*EINVAL*
    The scheduling policy was SCHED_SPORADIC and the specified low priority
    is invalid.

*EAGAIN*
    The system lacked the necessary resources to create another thread, or the
    self imposed limit on the total number of threads in a process
    PTHREAD_THREAD_MAX would be exceeded.

*EINVAL*
    Invalid argument passed.

**DESCRIPTION:**

The ``pthread_create`` routine is used to create a new thread with
the attributes specified by ``attr``. If the ``attr`` argument
is ``NULL``, then the default attribute set will be used. Modification
of the contents of ``attr`` after this thread is created does not
have an impact on this thread.

The thread begins execution at the address specified by ``start_routine``
with ``arg`` as its only argument. If ``start_routine`` returns,
then it is functionally equivalent to the thread executing the``pthread_exit`` service.

Upon successful completion, the ID of the created thread is returned in the``thread`` argument.

**NOTES:**

There is no concept of a single main thread in RTEMS as there is in
a tradition UNIX system. POSIX requires that the implicit return of
the main thread results in the same effects as if there were a call
to ``exit``. This does not occur in RTEMS.

The signal mask of the newly created thread is inherited from its
creator and the set of pending signals for this thread is empty.

pthread_exit - Terminate the Current Thread
-------------------------------------------
.. index:: pthread_exit
.. index:: terminate the current thread

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    void pthread_exit(
    void \*status
    );

**STATUS CODES:**

*NONE*

**DESCRIPTION:**

The ``pthread_exit`` routine is used to terminate the calling thread.
The ``status`` is made available to any successful join with the
terminating thread.

When a thread returns from its start routine, it results in an
implicit call to the ``pthread_exit`` routine with the return
value of the function serving as the argument to ``pthread_exit``.

**NOTES:**

Any cancellation cleanup handlers that hace been pushed and not yet popped
shall be popped in reverse of the order that they were pushed. After
all cancellation cleanup handlers have been executed, if the
thread has any thread-specific data, destructors for that data will
be invoked.

Thread termination does not release or free any application visible
resources including byt not limited to mutexes, file descriptors, allocated
memory, etc.. Similarly, exitting a thread does not result in any
process-oriented cleanup activity.

There is no concept of a single main thread in RTEMS as there is in
a tradition UNIX system. POSIX requires that the implicit return of
the main thread results in the same effects as if there were a call
to ``exit``. This does not occur in RTEMS.

All access to any automatic variables allocated by the threads is lost
when the thread exits. Thus references (i.e. pointers) to local variables
of a thread should not be used in a global manner without care. As
a specific example, a pointer to a local variable should NOT be used
as the return value.

pthread_detach - Detach a Thread
--------------------------------
.. index:: pthread_detach
.. index:: detach a thread

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_detach(
    pthread_t thread
    );

**STATUS CODES:**

*ESRCH*
    The thread specified is invalid.

*EINVAL*
    The thread specified is not a joinable thread.

**DESCRIPTION:**

The ``pthread_detach`` routine is used to to indicate that storage
for ``thread`` can be reclaimed when the thread terminates without
another thread joinging with it.

**NOTES:**

If any threads have previously joined with the specified thread, then they
will remain joined with that thread. Any subsequent calls to``pthread_join`` on the specified thread will fail.

.. COMMENT: pthread_getattr_np

pthread_getattr_np - Get Thread Attributes
------------------------------------------
.. index:: pthread_getattr_np
.. index:: get thread attributes

**CALLING SEQUENCE:**

.. code:: c

    #define _GNU_SOURCE
    #include <pthread.h>
    int pthread_getattr_np(
    pthread_t       thread,
    pthread_attr_t \*attr
    );

**STATUS CODES:**

*ESRCH*
    The thread specified is invalid.

*EINVAL*
    The attribute pointer argument is invalid.

**DESCRIPTION:**

The ``pthread_getattr_np`` routine is used to obtain the
attributes associated with ``thread``.

**NOTES:**

Modification of the execution modes and priority through the Classic API
may result in a combination that is not representable in the POSIX API.

pthread_join - Wait for Thread Termination
------------------------------------------
.. index:: pthread_join
.. index:: wait for thread termination

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_join(
    pthread_t    thread,
    void       \**value_ptr
    );

**STATUS CODES:**

*ESRCH*
    The thread specified is invalid.

*EINVAL*
    The thread specified is not a joinable thread.

*EDEADLK*
    A deadlock was detected or thread is the calling thread.

**DESCRIPTION:**

The ``pthread_join`` routine suspends execution of the calling thread
until ``thread`` terminates. If ``thread`` has already terminated,
then this routine returns immediately. The value returned by ``thread``
(i.e. passed to ``pthread_exit`` is returned in ``value_ptr``.

When this routine returns, then ``thread`` has been terminated.

**NOTES:**

The results of multiple simultaneous joins on the same thread is undefined.

If any threads have previously joined with the specified thread, then they
will remain joined with that thread. Any subsequent calls to``pthread_join`` on the specified thread will fail.

If value_ptr is NULL, then no value is returned.

pthread_self - Get Thread ID
----------------------------
.. index:: pthread_self
.. index:: get thread id

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    pthread_t pthread_self( void );

**STATUS CODES:**

The value returned is the ID of the calling thread.

**DESCRIPTION:**

This routine returns the ID of the calling thread.

**NOTES:**

NONE

pthread_equal - Compare Thread IDs
----------------------------------
.. index:: pthread_equal
.. index:: compare thread ids

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_equal(
    pthread_t t1,
    pthread_t t2
    );

**STATUS CODES:**

*zero*
    The thread ids are not equal.

*non-zero*
    The thread ids are equal.

**DESCRIPTION:**

The ``pthread_equal`` routine is used to compare two thread
IDs and determine if they are equal.

**NOTES:**

The behavior is undefined if the thread IDs are not valid.

pthread_once - Dynamic Package Initialization
---------------------------------------------
.. index:: pthread_once
.. index:: dynamic package initialization

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    pthread_once_t once_control = PTHREAD_ONCE_INIT;
    int pthread_once(
    pthread_once_t   \*once_control,
    void            (\*init_routine)(void)
    );

**STATUS CODES:**

NONE

**DESCRIPTION:**

The ``pthread_once`` routine is used to provide controlled initialization
of variables. The first call to ``pthread_once`` by any thread with the
same ``once_control`` will result in the ``init_routine`` being
invoked with no arguments. Subsequent calls to ``pthread_once`` with
the same ``once_control`` will have no effect.

The ``init_routine`` is guaranteed to have run to completion when
this routine returns to the caller.

**NOTES:**

The behavior of ``pthread_once`` is undefined if ``once_control``
is automatic storage (i.e. on a task stack) or is not initialized using``PTHREAD_ONCE_INIT``.

pthread_setschedparam - Set Thread Scheduling Parameters
--------------------------------------------------------
.. index:: pthread_setschedparam
.. index:: set thread scheduling parameters

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_setschedparam(
    pthread_t           thread,
    int                 policy,
    struct sched_param \*param
    );

**STATUS CODES:**

*EINVAL*
    The scheduling parameters indicated by the parameter param is invalid.

*EINVAL*
    The value specified by policy is invalid.

*EINVAL*
    The scheduling policy was SCHED_SPORADIC and the specified replenishment
    period is less than the initial budget.

*EINVAL*
    The scheduling policy was SCHED_SPORADIC and the specified low priority
    is invalid.

*ESRCH*
    The thread indicated was invalid.

**DESCRIPTION:**

The ``pthread_setschedparam`` routine is used to set the
scheduler parameters currently associated with the thread specified
by ``thread`` to the policy specified by ``policy``. The
contents of ``param`` are interpreted based upon the ``policy``
argument.

**NOTES:**

As required by POSIX, RTEMS defines the feature symbol``_POSIX_THREAD_PRIORITY_SCHEDULING`` to indicate that the
family of routines to which this routine belongs is supported.

pthread_getschedparam - Get Thread Scheduling Parameters
--------------------------------------------------------
.. index:: pthread_getschedparam
.. index:: get thread scheduling parameters

**CALLING SEQUENCE:**

.. code:: c

    #include <pthread.h>
    int pthread_getschedparam(
    pthread_t           thread,
    int                \*policy,
    struct sched_param \*param
    );

**STATUS CODES:**

*EINVAL*
    The policy pointer argument is invalid.

*EINVAL*
    The scheduling parameters pointer argument is invalid.

*ESRCH*
    The thread indicated by the parameter thread is invalid.

**DESCRIPTION:**

The ``pthread_getschedparam`` routine is used to obtain the
scheduler policy and parameters associated with ``thread``.
The current policy and associated parameters values returned in``policy`` and ``param``, respectively.

**NOTES:**

As required by POSIX, RTEMS defines the feature symbol``_POSIX_THREAD_PRIORITY_SCHEDULING`` to indicate that the
family of routines to which this routine belongs is supported.

.. COMMENT: pthread_getaffinity_np

pthread_getaffinity_np - Get Thread Affinity
--------------------------------------------

**CALLING SEQUENCE:**

.. code:: c

    #define _GNU_SOURCE
    #include <pthread.h>
    int pthread_getaffinity_np(
    const pthread_t       id,
    size_t                cpusetsize,
    cpu_set_t            \*cpuset
    );

**STATUS CODES:**

*EFAULT*
    The cpuset pointer argument is invalid.

*EINVAL*
    The ``cpusetsize`` does not match the value of ``affinitysetsize``
    field in the thread attribute object.

**DESCRIPTION:**

The ``pthread_getaffinity_np`` routine is used to obtain the``affinity.set`` field from the thread control object associated
with the ``id``.  The value of this field is returned in ``cpuset``.

**NOTES:**

NONE

.. COMMENT: pthread_setaffinity_np

pthread_setaffinity_np - Set Thread Affinity
--------------------------------------------

**CALLING SEQUENCE:**

.. code:: c

    #define _GNU_SOURCE
    #include <pthread.h>
    int pthread_setaffinity_np(
    pthread_t          id,
    size_t             cpusetsize,
    const cpu_set_t   \*cpuset
    );

**STATUS CODES:**

*EFAULT*
    The cpuset pointer argument is invalid.

*EINVAL*
    The ``cpusetsize`` does not match the value of ``affinitysetsize``
    field in the thread attribute object.

*EINVAL*
    The ``cpuset`` did not select a valid cpu.

*EINVAL*
    The ``cpuset`` selected a cpu that was invalid.

**DESCRIPTION:**

The ``pthread_setaffinity_np`` routine is used to set the``affinityset`` field of the thread object ``id``.
The value of this field is returned in ``cpuset``

**NOTES:**

NONE

.. COMMENT: COPYRIGHT (c) 1988-2002.

.. COMMENT: On-Line Applications Research Corporation (OAR).

.. COMMENT: All rights reserved.