Move the 3k reST doc tree in place.

1 files changed, 732 insertions, 0 deletions

diff --git a/Doc/library/threading.rst b/Doc/library/threading.rst
new file mode 100644
index 0000000..92ce02a
--- /dev/null
+++ b/Doc/library/threading.rst
@@ -0,0 +1,732 @@
+
+:mod:`threading` --- Higher-level threading interface
+=====================================================
+
+.. module:: threading
+   :synopsis: Higher-level threading interface.
+
+
+This module constructs higher-level threading interfaces on top of the  lower
+level :mod:`thread` module.
+
+The :mod:`dummy_threading` module is provided for situations where
+:mod:`threading` cannot be used because :mod:`thread` is missing.
+
+This module defines the following functions and objects:
+
+
+.. function:: activeCount()
+
+   Return the number of :class:`Thread` objects currently alive.  The returned
+   count is equal to the length of the list returned by :func:`enumerate`.
+
+
+.. function:: Condition()
+   :noindex:
+
+   A factory function that returns a new condition variable object. A condition
+   variable allows one or more threads to wait until they are notified by another
+   thread.
+
+
+.. function:: currentThread()
+
+   Return the current :class:`Thread` object, corresponding to the caller's thread
+   of control.  If the caller's thread of control was not created through the
+   :mod:`threading` module, a dummy thread object with limited functionality is
+   returned.
+
+
+.. function:: enumerate()
+
+   Return a list of all :class:`Thread` objects currently alive.  The list includes
+   daemonic threads, dummy thread objects created by :func:`currentThread`, and the
+   main thread.  It excludes terminated threads and threads that have not yet been
+   started.
+
+
+.. function:: Event()
+   :noindex:
+
+   A factory function that returns a new event object.  An event manages a flag
+   that can be set to true with the :meth:`set` method and reset to false with the
+   :meth:`clear` method.  The :meth:`wait` method blocks until the flag is true.
+
+
+.. class:: local
+
+   A class that represents thread-local data.  Thread-local data are data whose
+   values are thread specific.  To manage thread-local data, just create an
+   instance of :class:`local` (or a subclass) and store attributes on it::
+
+      mydata = threading.local()
+      mydata.x = 1
+
+   The instance's values will be different for separate threads.
+
+   For more details and extensive examples, see the documentation string of the
+   :mod:`_threading_local` module.
+
+   .. versionadded:: 2.4
+
+
+.. function:: Lock()
+
+   A factory function that returns a new primitive lock object.  Once a thread has
+   acquired it, subsequent attempts to acquire it block, until it is released; any
+   thread may release it.
+
+
+.. function:: RLock()
+
+   A factory function that returns a new reentrant lock object. A reentrant lock
+   must be released by the thread that acquired it. Once a thread has acquired a
+   reentrant lock, the same thread may acquire it again without blocking; the
+   thread must release it once for each time it has acquired it.
+
+
+.. function:: Semaphore([value])
+   :noindex:
+
+   A factory function that returns a new semaphore object.  A semaphore manages a
+   counter representing the number of :meth:`release` calls minus the number of
+   :meth:`acquire` calls, plus an initial value. The :meth:`acquire` method blocks
+   if necessary until it can return without making the counter negative.  If not
+   given, *value* defaults to 1.
+
+
+.. function:: BoundedSemaphore([value])
+
+   A factory function that returns a new bounded semaphore object.  A bounded
+   semaphore checks to make sure its current value doesn't exceed its initial
+   value.  If it does, :exc:`ValueError` is raised. In most situations semaphores
+   are used to guard resources with limited capacity.  If the semaphore is released
+   too many times it's a sign of a bug.  If not given, *value* defaults to 1.
+
+
+.. class:: Thread
+
+   A class that represents a thread of control.  This class can be safely
+   subclassed in a limited fashion.
+
+
+.. class:: Timer
+
+   A thread that executes a function after a specified interval has passed.
+
+
+.. function:: settrace(func)
+
+   .. index:: single: trace function
+
+   Set a trace function for all threads started from the :mod:`threading` module.
+   The *func* will be passed to  :func:`sys.settrace` for each thread, before its
+   :meth:`run` method is called.
+
+   .. versionadded:: 2.3
+
+
+.. function:: setprofile(func)
+
+   .. index:: single: profile function
+
+   Set a profile function for all threads started from the :mod:`threading` module.
+   The *func* will be passed to  :func:`sys.setprofile` for each thread, before its
+   :meth:`run` method is called.
+
+   .. versionadded:: 2.3
+
+
+.. function:: stack_size([size])
+
+   Return the thread stack size used when creating new threads.  The optional
+   *size* argument specifies the stack size to be used for subsequently created
+   threads, and must be 0 (use platform or configured default) or a positive
+   integer value of at least 32,768 (32kB). If changing the thread stack size is
+   unsupported, a :exc:`ThreadError` is raised.  If the specified stack size is
+   invalid, a :exc:`ValueError` is raised and the stack size is unmodified.  32kB
+   is currently the minimum supported stack size value to guarantee sufficient
+   stack space for the interpreter itself.  Note that some platforms may have
+   particular restrictions on values for the stack size, such as requiring a
+   minimum stack size > 32kB or requiring allocation in multiples of the system
+   memory page size - platform documentation should be referred to for more
+   information (4kB pages are common; using multiples of 4096 for the stack size is
+   the suggested approach in the absence of more specific information).
+   Availability: Windows, systems with POSIX threads.
+
+   .. versionadded:: 2.5
+
+Detailed interfaces for the objects are documented below.
+
+The design of this module is loosely based on Java's threading model. However,
+where Java makes locks and condition variables basic behavior of every object,
+they are separate objects in Python.  Python's :class:`Thread` class supports a
+subset of the behavior of Java's Thread class; currently, there are no
+priorities, no thread groups, and threads cannot be destroyed, stopped,
+suspended, resumed, or interrupted.  The static methods of Java's Thread class,
+when implemented, are mapped to module-level functions.
+
+All of the methods described below are executed atomically.
+
+
+.. _lock-objects:
+
+Lock Objects
+------------
+
+A primitive lock is a synchronization primitive that is not owned by a
+particular thread when locked.  In Python, it is currently the lowest level
+synchronization primitive available, implemented directly by the :mod:`thread`
+extension module.
+
+A primitive lock is in one of two states, "locked" or "unlocked". It is created
+in the unlocked state.  It has two basic methods, :meth:`acquire` and
+:meth:`release`.  When the state is unlocked, :meth:`acquire` changes the state
+to locked and returns immediately.  When the state is locked, :meth:`acquire`
+blocks until a call to :meth:`release` in another thread changes it to unlocked,
+then the :meth:`acquire` call resets it to locked and returns.  The
+:meth:`release` method should only be called in the locked state; it changes the
+state to unlocked and returns immediately. If an attempt is made to release an
+unlocked lock, a :exc:`RuntimeError` will be raised.
+
+When more than one thread is blocked in :meth:`acquire` waiting for the state to
+turn to unlocked, only one thread proceeds when a :meth:`release` call resets
+the state to unlocked; which one of the waiting threads proceeds is not defined,
+and may vary across implementations.
+
+All methods are executed atomically.
+
+
+.. method:: Lock.acquire([blocking=1])
+
+   Acquire a lock, blocking or non-blocking.
+
+   When invoked without arguments, block until the lock is unlocked, then set it to
+   locked, and return true.
+
+   When invoked with the *blocking* argument set to true, do the same thing as when
+   called without arguments, and return true.
+
+   When invoked with the *blocking* argument set to false, do not block.  If a call
+   without an argument would block, return false immediately; otherwise, do the
+   same thing as when called without arguments, and return true.
+
+
+.. method:: Lock.release()
+
+   Release a lock.
+
+   When the lock is locked, reset it to unlocked, and return.  If any other threads
+   are blocked waiting for the lock to become unlocked, allow exactly one of them
+   to proceed.
+
+   Do not call this method when the lock is unlocked.
+
+   There is no return value.
+
+
+.. _rlock-objects:
+
+RLock Objects
+-------------
+
+A reentrant lock is a synchronization primitive that may be acquired multiple
+times by the same thread.  Internally, it uses the concepts of "owning thread"
+and "recursion level" in addition to the locked/unlocked state used by primitive
+locks.  In the locked state, some thread owns the lock; in the unlocked state,
+no thread owns it.
+
+To lock the lock, a thread calls its :meth:`acquire` method; this returns once
+the thread owns the lock.  To unlock the lock, a thread calls its
+:meth:`release` method. :meth:`acquire`/:meth:`release` call pairs may be
+nested; only the final :meth:`release` (the :meth:`release` of the outermost
+pair) resets the lock to unlocked and allows another thread blocked in
+:meth:`acquire` to proceed.
+
+
+.. method:: RLock.acquire([blocking=1])
+
+   Acquire a lock, blocking or non-blocking.
+
+   When invoked without arguments: if this thread already owns the lock, increment
+   the recursion level by one, and return immediately.  Otherwise, if another
+   thread owns the lock, block until the lock is unlocked.  Once the lock is
+   unlocked (not owned by any thread), then grab ownership, set the recursion level
+   to one, and return.  If more than one thread is blocked waiting until the lock
+   is unlocked, only one at a time will be able to grab ownership of the lock.
+   There is no return value in this case.
+
+   When invoked with the *blocking* argument set to true, do the same thing as when
+   called without arguments, and return true.
+
+   When invoked with the *blocking* argument set to false, do not block.  If a call
+   without an argument would block, return false immediately; otherwise, do the
+   same thing as when called without arguments, and return true.
+
+
+.. method:: RLock.release()
+
+   Release a lock, decrementing the recursion level.  If after the decrement it is
+   zero, reset the lock to unlocked (not owned by any thread), and if any other
+   threads are blocked waiting for the lock to become unlocked, allow exactly one
+   of them to proceed.  If after the decrement the recursion level is still
+   nonzero, the lock remains locked and owned by the calling thread.
+
+   Only call this method when the calling thread owns the lock. A
+   :exc:`RuntimeError` is raised if this method is called when the lock is
+   unlocked.
+
+   There is no return value.
+
+
+.. _condition-objects:
+
+Condition Objects
+-----------------
+
+A condition variable is always associated with some kind of lock; this can be
+passed in or one will be created by default.  (Passing one in is useful when
+several condition variables must share the same lock.)
+
+A condition variable has :meth:`acquire` and :meth:`release` methods that call
+the corresponding methods of the associated lock. It also has a :meth:`wait`
+method, and :meth:`notify` and :meth:`notifyAll` methods.  These three must only
+be called when the calling thread has acquired the lock, otherwise a
+:exc:`RuntimeError` is raised.
+
+The :meth:`wait` method releases the lock, and then blocks until it is awakened
+by a :meth:`notify` or :meth:`notifyAll` call for the same condition variable in
+another thread.  Once awakened, it re-acquires the lock and returns.  It is also
+possible to specify a timeout.
+
+The :meth:`notify` method wakes up one of the threads waiting for the condition
+variable, if any are waiting.  The :meth:`notifyAll` method wakes up all threads
+waiting for the condition variable.
+
+Note: the :meth:`notify` and :meth:`notifyAll` methods don't release the lock;
+this means that the thread or threads awakened will not return from their
+:meth:`wait` call immediately, but only when the thread that called
+:meth:`notify` or :meth:`notifyAll` finally relinquishes ownership of the lock.
+
+Tip: the typical programming style using condition variables uses the lock to
+synchronize access to some shared state; threads that are interested in a
+particular change of state call :meth:`wait` repeatedly until they see the
+desired state, while threads that modify the state call :meth:`notify` or
+:meth:`notifyAll` when they change the state in such a way that it could
+possibly be a desired state for one of the waiters.  For example, the following
+code is a generic producer-consumer situation with unlimited buffer capacity::
+
+   # Consume one item
+   cv.acquire()
+   while not an_item_is_available():
+       cv.wait()
+   get_an_available_item()
+   cv.release()
+
+   # Produce one item
+   cv.acquire()
+   make_an_item_available()
+   cv.notify()
+   cv.release()
+
+To choose between :meth:`notify` and :meth:`notifyAll`, consider whether one
+state change can be interesting for only one or several waiting threads.  E.g.
+in a typical producer-consumer situation, adding one item to the buffer only
+needs to wake up one consumer thread.
+
+
+.. class:: Condition([lock])
+
+   If the *lock* argument is given and not ``None``, it must be a :class:`Lock` or
+   :class:`RLock` object, and it is used as the underlying lock.  Otherwise, a new
+   :class:`RLock` object is created and used as the underlying lock.
+
+
+.. method:: Condition.acquire(*args)
+
+   Acquire the underlying lock. This method calls the corresponding method on the
+   underlying lock; the return value is whatever that method returns.
+
+
+.. method:: Condition.release()
+
+   Release the underlying lock. This method calls the corresponding method on the
+   underlying lock; there is no return value.
+
+
+.. method:: Condition.wait([timeout])
+
+   Wait until notified or until a timeout occurs. If the calling thread has not
+   acquired the lock when this method is called, a :exc:`RuntimeError` is raised.
+
+   This method releases the underlying lock, and then blocks until it is awakened
+   by a :meth:`notify` or :meth:`notifyAll` call for the same condition variable in
+   another thread, or until the optional timeout occurs.  Once awakened or timed
+   out, it re-acquires the lock and returns.
+
+   When the *timeout* argument is present and not ``None``, it should be a floating
+   point number specifying a timeout for the operation in seconds (or fractions
+   thereof).
+
+   When the underlying lock is an :class:`RLock`, it is not released using its
+   :meth:`release` method, since this may not actually unlock the lock when it was
+   acquired multiple times recursively.  Instead, an internal interface of the
+   :class:`RLock` class is used, which really unlocks it even when it has been
+   recursively acquired several times. Another internal interface is then used to
+   restore the recursion level when the lock is reacquired.
+
+
+.. method:: Condition.notify()
+
+   Wake up a thread waiting on this condition, if any. Wait until notified or until
+   a timeout occurs. If the calling thread has not acquired the lock when this
+   method is called, a :exc:`RuntimeError` is raised.
+
+   This method wakes up one of the threads waiting for the condition variable, if
+   any are waiting; it is a no-op if no threads are waiting.
+
+   The current implementation wakes up exactly one thread, if any are waiting.
+   However, it's not safe to rely on this behavior.  A future, optimized
+   implementation may occasionally wake up more than one thread.
+
+   Note: the awakened thread does not actually return from its :meth:`wait` call
+   until it can reacquire the lock.  Since :meth:`notify` does not release the
+   lock, its caller should.
+
+
+.. method:: Condition.notifyAll()
+
+   Wake up all threads waiting on this condition.  This method acts like
+   :meth:`notify`, but wakes up all waiting threads instead of one. If the calling
+   thread has not acquired the lock when this method is called, a
+   :exc:`RuntimeError` is raised.
+
+
+.. _semaphore-objects:
+
+Semaphore Objects
+-----------------
+
+This is one of the oldest synchronization primitives in the history of computer
+science, invented by the early Dutch computer scientist Edsger W. Dijkstra (he
+used :meth:`P` and :meth:`V` instead of :meth:`acquire` and :meth:`release`).
+
+A semaphore manages an internal counter which is decremented by each
+:meth:`acquire` call and incremented by each :meth:`release` call.  The counter
+can never go below zero; when :meth:`acquire` finds that it is zero, it blocks,
+waiting until some other thread calls :meth:`release`.
+
+
+.. class:: Semaphore([value])
+
+   The optional argument gives the initial *value* for the internal counter; it
+   defaults to ``1``. If the *value* given is less than 0, :exc:`ValueError` is
+   raised.
+
+
+.. method:: Semaphore.acquire([blocking])
+
+   Acquire a semaphore.
+
+   When invoked without arguments: if the internal counter is larger than zero on
+   entry, decrement it by one and return immediately.  If it is zero on entry,
+   block, waiting until some other thread has called :meth:`release` to make it
+   larger than zero.  This is done with proper interlocking so that if multiple
+   :meth:`acquire` calls are blocked, :meth:`release` will wake exactly one of them
+   up.  The implementation may pick one at random, so the order in which blocked
+   threads are awakened should not be relied on.  There is no return value in this
+   case.
+
+   When invoked with *blocking* set to true, do the same thing as when called
+   without arguments, and return true.
+
+   When invoked with *blocking* set to false, do not block.  If a call without an
+   argument would block, return false immediately; otherwise, do the same thing as
+   when called without arguments, and return true.
+
+
+.. method:: Semaphore.release()
+
+   Release a semaphore, incrementing the internal counter by one.  When it was zero
+   on entry and another thread is waiting for it to become larger than zero again,
+   wake up that thread.
+
+
+.. _semaphore-examples:
+
+:class:`Semaphore` Example
+^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Semaphores are often used to guard resources with limited capacity, for example,
+a database server.  In any situation where the size of the resource size is
+fixed, you should use a bounded semaphore.  Before spawning any worker threads,
+your main thread would initialize the semaphore::
+
+   maxconnections = 5
+   ...
+   pool_sema = BoundedSemaphore(value=maxconnections)
+
+Once spawned, worker threads call the semaphore's acquire and release methods
+when they need to connect to the server::
+
+   pool_sema.acquire()
+   conn = connectdb()
+   ... use connection ...
+   conn.close()
+   pool_sema.release()
+
+The use of a bounded semaphore reduces the chance that a programming error which
+causes the semaphore to be released more than it's acquired will go undetected.
+
+
+.. _event-objects:
+
+Event Objects
+-------------
+
+This is one of the simplest mechanisms for communication between threads: one
+thread signals an event and other threads wait for it.
+
+An event object manages an internal flag that can be set to true with the
+:meth:`set` method and reset to false with the :meth:`clear` method.  The
+:meth:`wait` method blocks until the flag is true.
+
+
+.. class:: Event()
+
+   The internal flag is initially false.
+
+
+.. method:: Event.isSet()
+
+   Return true if and only if the internal flag is true.
+
+
+.. method:: Event.set()
+
+   Set the internal flag to true. All threads waiting for it to become true are
+   awakened. Threads that call :meth:`wait` once the flag is true will not block at
+   all.
+
+
+.. method:: Event.clear()
+
+   Reset the internal flag to false. Subsequently, threads calling :meth:`wait`
+   will block until :meth:`set` is called to set the internal flag to true again.
+
+
+.. method:: Event.wait([timeout])
+
+   Block until the internal flag is true. If the internal flag is true on entry,
+   return immediately.  Otherwise, block until another thread calls :meth:`set` to
+   set the flag to true, or until the optional timeout occurs.
+
+   When the timeout argument is present and not ``None``, it should be a floating
+   point number specifying a timeout for the operation in seconds (or fractions
+   thereof).
+
+
+.. _thread-objects:
+
+Thread Objects
+--------------
+
+This class represents an activity that is run in a separate thread of control.
+There are two ways to specify the activity: by passing a callable object to the
+constructor, or by overriding the :meth:`run` method in a subclass.  No other
+methods (except for the constructor) should be overridden in a subclass.  In
+other words,  *only*  override the :meth:`__init__` and :meth:`run` methods of
+this class.
+
+Once a thread object is created, its activity must be started by calling the
+thread's :meth:`start` method.  This invokes the :meth:`run` method in a
+separate thread of control.
+
+Once the thread's activity is started, the thread is considered 'alive'. It
+stops being alive when its :meth:`run` method terminates -- either normally, or
+by raising an unhandled exception.  The :meth:`isAlive` method tests whether the
+thread is alive.
+
+Other threads can call a thread's :meth:`join` method.  This blocks the calling
+thread until the thread whose :meth:`join` method is called is terminated.
+
+A thread has a name.  The name can be passed to the constructor, set with the
+:meth:`setName` method, and retrieved with the :meth:`getName` method.
+
+A thread can be flagged as a "daemon thread".  The significance of this flag is
+that the entire Python program exits when only daemon threads are left.  The
+initial value is inherited from the creating thread.  The flag can be set with
+the :meth:`setDaemon` method and retrieved with the :meth:`isDaemon` method.
+
+There is a "main thread" object; this corresponds to the initial thread of
+control in the Python program.  It is not a daemon thread.
+
+There is the possibility that "dummy thread objects" are created. These are
+thread objects corresponding to "alien threads", which are threads of control
+started outside the threading module, such as directly from C code.  Dummy
+thread objects have limited functionality; they are always considered alive and
+daemonic, and cannot be :meth:`join`\ ed.  They are never deleted, since it is
+impossible to detect the termination of alien threads.
+
+
+.. class:: Thread(group=None, target=None, name=None, args=(), kwargs={})
+
+   This constructor should always be called with keyword arguments.  Arguments are:
+
+   *group* should be ``None``; reserved for future extension when a
+   :class:`ThreadGroup` class is implemented.
+
+   *target* is the callable object to be invoked by the :meth:`run` method.
+   Defaults to ``None``, meaning nothing is called.
+
+   *name* is the thread name.  By default, a unique name is constructed of the form
+   "Thread-*N*" where *N* is a small decimal number.
+
+   *args* is the argument tuple for the target invocation.  Defaults to ``()``.
+
+   *kwargs* is a dictionary of keyword arguments for the target invocation.
+   Defaults to ``{}``.
+
+   If the subclass overrides the constructor, it must make sure to invoke the base
+   class constructor (``Thread.__init__()``) before doing anything else to the
+   thread.
+
+
+.. method:: Thread.start()
+
+   Start the thread's activity.
+
+   It must be called at most once per thread object.  It arranges for the object's
+   :meth:`run` method to be invoked in a separate thread of control.
+
+   This method will raise a :exc:`RuntimeException` if called more than once on the
+   same thread object.
+
+
+.. method:: Thread.run()
+
+   Method representing the thread's activity.
+
+   You may override this method in a subclass.  The standard :meth:`run` method
+   invokes the callable object passed to the object's constructor as the *target*
+   argument, if any, with sequential and keyword arguments taken from the *args*
+   and *kwargs* arguments, respectively.
+
+
+.. method:: Thread.join([timeout])
+
+   Wait until the thread terminates. This blocks the calling thread until the
+   thread whose :meth:`join` method is called terminates -- either normally or
+   through an unhandled exception -- or until the optional timeout occurs.
+
+   When the *timeout* argument is present and not ``None``, it should be a floating
+   point number specifying a timeout for the operation in seconds (or fractions
+   thereof). As :meth:`join` always  returns ``None``, you must call
+   :meth:`isAlive` to decide whether  a timeout happened.
+
+   When the *timeout* argument is not present or ``None``, the operation will block
+   until the thread terminates.
+
+   A thread can be :meth:`join`\ ed many times.
+
+   :meth:`join` may throw a :exc:`RuntimeError`, if an attempt is made to join the
+   current thread as that would cause a deadlock. It is also an error to
+   :meth:`join` a thread before it has been started and attempts to do so raises
+   same exception.
+
+
+.. method:: Thread.getName()
+
+   Return the thread's name.
+
+
+.. method:: Thread.setName(name)
+
+   Set the thread's name.
+
+   The name is a string used for identification purposes only. It has no semantics.
+   Multiple threads may be given the same name.  The initial name is set by the
+   constructor.
+
+
+.. method:: Thread.isAlive()
+
+   Return whether the thread is alive.
+
+   Roughly, a thread is alive from the moment the :meth:`start` method returns
+   until its :meth:`run` method terminates. The module function :func:`enumerate`
+   returns a list of all alive threads.
+
+
+.. method:: Thread.isDaemon()
+
+   Return the thread's daemon flag.
+
+
+.. method:: Thread.setDaemon(daemonic)
+
+   Set the thread's daemon flag to the Boolean value *daemonic*. This must be
+   called before :meth:`start` is called, otherwise :exc:`RuntimeError` is raised.
+
+   The initial value is inherited from the creating thread.
+
+   The entire Python program exits when no alive non-daemon threads are left.
+
+
+.. _timer-objects:
+
+Timer Objects
+-------------
+
+This class represents an action that should be run only after a certain amount
+of time has passed --- a timer.  :class:`Timer` is a subclass of :class:`Thread`
+and as such also functions as an example of creating custom threads.
+
+Timers are started, as with threads, by calling their :meth:`start` method.  The
+timer can be stopped (before its action has begun) by calling the :meth:`cancel`
+method.  The interval the timer will wait before executing its action may not be
+exactly the same as the interval specified by the user.
+
+For example::
+
+   def hello():
+       print "hello, world"
+
+   t = Timer(30.0, hello)
+   t.start() # after 30 seconds, "hello, world" will be printed
+
+
+.. class:: Timer(interval, function, args=[], kwargs={})
+
+   Create a timer that will run *function* with arguments *args* and  keyword
+   arguments *kwargs*, after *interval* seconds have passed.
+
+
+.. method:: Timer.cancel()
+
+   Stop the timer, and cancel the execution of the timer's action.  This will only
+   work if the timer is still in its waiting stage.
+
+
+.. _with-locks:
+
+Using locks, conditions, and semaphores in the :keyword:`with` statement
+------------------------------------------------------------------------
+
+All of the objects provided by this module that have :meth:`acquire` and
+:meth:`release` methods can be used as context managers for a :keyword:`with`
+statement.  The :meth:`acquire` method will be called when the block is entered,
+and :meth:`release` will be called when the block is exited.
+
+Currently, :class:`Lock`, :class:`RLock`, :class:`Condition`,
+:class:`Semaphore`, and :class:`BoundedSemaphore` objects may be used as
+:keyword:`with` statement context managers.  For example::
+
+   from __future__ import with_statement
+   import threading
+
+   some_rlock = threading.RLock()
+
+   with some_rlock:
+       print "some_rlock is locked while this executes"
+