Update side effect document

Author: aisk

Doc/library/multiprocessing.rst

@@ -867,6 +867,10 @@ For an example of the usage of queues for interprocess communication see
    locks/semaphores.  When a process first puts an item on the queue a feeder
    thread is started which transfers objects from a buffer into the pipe.
 
+   If the global start method has not been set, calling this function will
+   have the side effect of setting the current global start method.
+   See the :func:`get_context` function.
+
    The usual :exc:`queue.Empty` and :exc:`queue.Full` exceptions from the
    standard library's :mod:`queue` module are raised to signal timeouts.
 
@@ -977,6 +981,10 @@ For an example of the usage of queues for interprocess communication see
 
    It is a simplified :class:`Queue` type, very close to a locked :class:`Pipe`.
 
+   If the global start method has not been set, calling this function will
+   have the side effect of setting the current global start method.
+   See the :func:`get_context` function.
+
    .. method:: close()
 
       Close the queue: release internal resources.
@@ -1007,6 +1015,10 @@ For an example of the usage of queues for interprocess communication see
    :class:`JoinableQueue`, a :class:`Queue` subclass, is a queue which
    additionally has :meth:`task_done` and :meth:`join` methods.
 
+   If the global start method has not been set, calling this function will
+   have the side effect of setting the current global start method.
+   See the :func:`get_context` function.
+
    .. method:: task_done()
 
       Indicate that a formerly enqueued task is complete. Used by queue
@@ -1361,13 +1373,21 @@ object -- see :ref:`multiprocessing-managers`.
 
    A barrier object: a clone of :class:`threading.Barrier`.
 
+   If the global start method has not been set, calling this function will
+   have the side effect of setting the current global start method.
+   See the :func:`get_context` function.
+
    .. versionadded:: 3.3
 
 .. class:: BoundedSemaphore([value])
 
    A bounded semaphore object: a close analog of
    :class:`threading.BoundedSemaphore`.
 
+   If the global start method has not been set, calling this function will
+   have the side effect of setting the current global start method.
+   See the :func:`get_context` function.
+
    A solitary difference from its close analog exists: its ``acquire`` method's
    first argument is named *block*, as is consistent with :meth:`Lock.acquire`.
 
@@ -1388,13 +1408,20 @@ object -- see :ref:`multiprocessing-managers`.
    If *lock* is specified then it should be a :class:`Lock` or :class:`RLock`
    object from :mod:`multiprocessing`.
 
+   If the global start method has not been set, calling this function will
+   have the side effect of setting the current global start method.
+   See the :func:`get_context` function.
+
    .. versionchanged:: 3.3
       The :meth:`~threading.Condition.wait_for` method was added.
 
 .. class:: Event()
 
    A clone of :class:`threading.Event`.
 
+   If the global start method has not been set, calling this function will
+   have the side effect of setting the current global start method.
+   See the :func:`get_context` function.
 
 .. class:: Lock()
 
@@ -1410,6 +1437,10 @@ object -- see :ref:`multiprocessing-managers`.
    instance of ``multiprocessing.synchronize.Lock`` initialized with a
    default context.
 
+   If the global start method has not been set, calling this function will
+   have the side effect of setting the current global start method.
+   See the :func:`get_context` function.
+
    :class:`Lock` supports the :term:`context manager` protocol and thus may be
    used in :keyword:`with` statements.
 
@@ -1467,6 +1498,10 @@ object -- see :ref:`multiprocessing-managers`.
    instance of ``multiprocessing.synchronize.RLock`` initialized with a
    default context.
 
+   If the global start method has not been set, calling this function will
+   have the side effect of setting the current global start method.
+   See the :func:`get_context` function.
+
    :class:`RLock` supports the :term:`context manager` protocol and thus may be
    used in :keyword:`with` statements.
 
@@ -1526,6 +1561,10 @@ object -- see :ref:`multiprocessing-managers`.
 
    A semaphore object: a close analog of :class:`threading.Semaphore`.
 
+   If the global start method has not been set, calling this function will
+   have the side effect of setting the current global start method.
+   See the :func:`get_context` function.
+
    A solitary difference from its close analog exists: its ``acquire`` method's
    first argument is named *block*, as is consistent with :meth:`Lock.acquire`.
 
@@ -2330,7 +2369,9 @@ with the :class:`Pool` class.
    the worker processes.  Usually a pool is created using the
    function :func:`multiprocessing.Pool` or the :meth:`Pool` method
    of a context object.  In both cases *context* is set
-   appropriately.
+   appropriately. If ``None``, calling this function will have the side effect
+   of setting the current global start method if it has not been set already.
+   See the :func:`get_context` function.
 
    Note that the methods of the pool object should only be called by
    the process which created the pool.