1 files changed, 48 insertions, 0 deletions
diff --git a/Doc/library/asyncio-dev.rst b/Doc/library/asyncio-dev.rst
index 7083e60061..ce1275b4e0 100644
--- a/Doc/library/asyncio-dev.rst
+++ b/Doc/library/asyncio-dev.rst
@@ -40,6 +40,43 @@ Examples of effects of the debug mode:
    <asyncio-logger>`.
 
 
+Cancellation
+------------
+
+Cancellation of tasks is not common in classic programming. In asynchronous
+programming, not only it is something common, but you have to prepare your
+code to handle it.
+
+Futures and tasks can be cancelled explicitly with their :meth:`Future.cancel`
+method. The :func:`wait_for` function cancels the waited task when the timeout
+occurs. There are many other cases where a task can be cancelled indirectly.
+
+Don't call :meth:`~Future.set_result` or :meth:`~Future.set_exception` method
+of :class:`Future` if the future is cancelled: it would fail with an exception.
+For example, write::
+
+    if not fut.cancelled():
+        fut.set_result('done')
+
+Don't schedule directly a call to the :meth:`~Future.set_result` or the
+:meth:`~Future.set_exception` method of a future with
+:meth:`BaseEventLoop.call_soon`: the future can be cancelled before its method
+is called.
+
+If you wait for a future, you should check early if the future was cancelled to
+avoid useless operations. Example::
+
+    @coroutine
+    def slow_operation(fut):
+        if fut.cancelled():
+            return
+        # ... slow computation ...
+        yield from fut
+        # ...
+
+The :func:`shield` function can also be used to ignore cancellation.
+
+
 .. _asyncio-multithreading:
 
 Concurrency and multithreading
@@ -335,3 +372,14 @@ traceback where the task was created. Example of log in debug mode::
 
    :ref:`Detect coroutine objects never scheduled <asyncio-coroutine-not-scheduled>`.
 
+
+Close transports
+----------------
+
+When a transport is no more needed, call its ``close()`` method to release
+resources.
+
+If a transport (or an event loop) is not closed explicitly, a
+:exc:`ResourceWarning` warning will be emitted in its destructor. The
+:exc:`ResourceWarning` warnings are hidden by default: use the ``-Wd`` command
+line option of Python to show them.