Clarified async documentation.

docs/spelling_wordlist

@@ -144,7 +144,6 @@ databrowse
 datafile
 dataset
 datasets
-datastores
 datatype
 datetimes
 Debian

docs/topics/async.txt

@@ -8,15 +8,15 @@ Asynchronous support
 
 Django has support for writing asynchronous ("async") views, along with an
 entirely async-enabled request stack if you are running under
-:doc:`ASGI </howto/deployment/asgi/index>` rather than WSGI. Async views will
+:doc:`ASGI </howto/deployment/asgi/index>`. Async views will still work under
-still work under WSGI, but with performance penalties, and without the ability
+WSGI, but with performance penalties, and without the ability to have efficient
-to have efficient long-running requests.
+long-running requests.
 
-We're still working on asynchronous support for the ORM and other parts of
+We're still working on async support for the ORM and other parts of Django.
-Django; you can expect to see these in future releases. For now, you can use
+You can expect to see this in future releases. For now, you can use the
-the :func:`sync_to_async` adapter to interact with normal Django, as well as
+:func:`sync_to_async` adapter to interact with the sync parts of Django.
-use a whole range of Python asyncio libraries natively. See below for more
+There is also a whole range of async-native Python libraries that you can
-details.
+integrate with.
 
 .. versionchanged:: 3.1
 
@@ -40,20 +40,21 @@ class-based view, this means making its ``__call__()`` method an ``async def``
     coroutine, ensure you set the ``_is_coroutine`` attribute of the view
     to ``asyncio.coroutines._is_coroutine`` so this function returns ``True``.
 
-Under a WSGI server, asynchronous views will run in their own, one-off event
+Under a WSGI server, async views will run in their own, one-off event loop.
-loop. This means that you can do things like parallel, async HTTP calls to APIs
+This means you can use async features, like parallel async HTTP requests,
-without any issues, but you will not get the benefits of an asynchronous
+without any issues, but you will not get the benefits of an async stack.
-request stack.
 
-If you want these benefits - which are mostly around the ability to service
+The main benefits are the ability to service hundreds of connections without
-hundreds of connections without using any Python threads (enabling slow
+using Python threads. This allows you to use slow streaming, long-polling, and
-streaming, long-polling, and other exciting response types) - you will need to
+other exciting response types.
-deploy Django using :doc:`ASGI </howto/deployment/asgi/index>` instead.
+
+If you want to use these, you will need to deploy Django using
+:doc:`ASGI </howto/deployment/asgi/index>` instead.
 
 .. warning::
 
     You will only get the benefits of a fully-asynchronous request stack if you
-    have *no synchronous middleware* loaded into your site; if there is a piece
+    have *no synchronous middleware* loaded into your site. If there is a piece
     of synchronous middleware, then Django must use a thread per request to
     safely emulate a synchronous environment for it.
 
@@ -63,22 +64,30 @@ deploy Django using :doc:`ASGI </howto/deployment/asgi/index>` instead.
     on debug logging for the ``django.request`` logger and look for log
     messages about *`"Synchronous middleware ... adapted"*.
 
-In either ASGI or WSGI mode, though, you can safely use asynchronous support to
+In both ASGI and WSGI mode, you can still safely use asynchronous support to
-run code in parallel rather than serially, which is especially handy when
+run code in parallel rather than serially. This is especially handy when
-dealing with external APIs or datastores.
+dealing with external APIs or data stores.
 
-If you want to call a part of Django that is still synchronous (like the ORM)
+If you want to call a part of Django that is still synchronous, like the ORM,
-you will need to wrap it in a :func:`sync_to_async` call, like this::
+you will need to wrap it in a :func:`sync_to_async` call. For example::
 
     from asgiref.sync import sync_to_async
 
-    results = sync_to_async(MyModel.objects.get)(pk=123)
+    results = sync_to_async(Blog.objects.get)(pk=123)
 
 You may find it easier to move any ORM code into its own function and call that
-entire function using :func:`sync_to_async`. If you accidentally try to call
+entire function using :func:`sync_to_async`. For example::
-part of Django that is still synchronous-only from an async view, you will
+
-trigger Django's :ref:`asynchronous safety protection <async-safety>` to
+    from asgiref.sync import sync_to_async
-protect your data from corruption.
+
+    @sync_to_async
+    def get_blog(pk):
+        return Blog.objects.select_related('author').get(pk=pk)
+
+If you accidentally try to call a part of Django that is still synchronous-only
+from an async view, you will trigger Django's
+:ref:`asynchronous safety protection <async-safety>` to protect your data from
+corruption.
 
 Performance
 -----------
@@ -88,56 +97,56 @@ WSGI, or a traditional sync view under ASGI), Django must emulate the other
 call style to allow your code to run. This context-switch causes a small
 performance penalty of around a millisecond.
 
-This is true of middleware as well, however. Django will attempt to minimize
+This is also true of middleware. Django will attempt to minimize the number of
-the number of context-switches. If you have an ASGI server, but all your
+context-switches between sync and async. If you have an ASGI server, but all
-middleware and views are synchronous, it will switch just once, before it
+your middleware and views are synchronous, it will switch just once, before it
 enters the middleware stack.
 
-If, however, you put synchronous middleware between an ASGI server and an
+However, if you put synchronous middleware between an ASGI server and an
 asynchronous view, it will have to switch into sync mode for the middleware and
-then back to asynchronous mode for the view, holding the synchronous thread
+then back to async mode for the view. Django will also hold the sync thread
-open for middleware exception propagation. This may not be noticeable, but bear
+open for middleware exception propagation. This may not be noticeable at first,
-in mind that even adding a single piece of synchronous middleware can drag your
+but adding this penalty of one thread per request can remove any async
-whole async project down to running with one thread per request, and the
+performance advantage.
-associated performance penalties.
 
-You should do your own performance testing to see what effect ASGI vs. WSGI has
+You should do your own performance testing to see what effect ASGI versus WSGI
-on your code. In some cases, there may be a performance increase even for
+has on your code. In some cases, there may be a performance increase even for
-purely-synchronous codebase under ASGI because the request-handling code is
+a purely synchronous codebase under ASGI because the request-handling code is
-still all running asynchronously. In general, though, you will only want to
+still all running asynchronously. In general you will only want to enable ASGI
-enable ASGI mode if you have asynchronous code in your site.
+mode if you have asynchronous code in your project.
 
 .. _async-safety:
 
-Async-safety
+Async safety
 ============
 
-Certain key parts of Django are not able to operate safely in an asynchronous
+Certain key parts of Django are not able to operate safely in an async
 environment, as they have global state that is not coroutine-aware. These parts
 of Django are classified as "async-unsafe", and are protected from execution in
-an asynchronous environment. The ORM is the main example, but there are other
+an async environment. The ORM is the main example, but there are other parts
-parts that are also protected in this way.
+that are also protected in this way.
 
 If you try to run any of these parts from a thread where there is a *running
 event loop*, you will get a
 :exc:`~django.core.exceptions.SynchronousOnlyOperation` error. Note that you
 don't have to be inside an async function directly to have this error occur. If
-you have called a synchronous function directly from an asynchronous function
+you have called a sync function directly from an async function,
-without going through something like :func:`sync_to_async` or a threadpool,
+without using :func:`sync_to_async` or similar, then it can also occur. This is
-then it can also occur, as your code is still running in an asynchronous
+because your code is still running in a thread with an active event loop, even
-context.
+though it may not be declared as async code.
 
 If you encounter this error, you should fix your code to not call the offending
-code from an async context; instead, write your code that talks to async-unsafe
+code from an async context. Instead, write your code that talks to async-unsafe
-in its own, synchronous function, and call that using
+functions in its own, sync function, and call that using
-:func:`asgiref.sync.sync_to_async`, or any other preferred way of running
+:func:`asgiref.sync.sync_to_async` (or any other way of running sync code in
-synchronous code in its own thread.
+its own thread).
 
-If you are *absolutely* in dire need to run this code from an asynchronous
+You may still be forced to run sync code from an async context. For example,
-context - for example, it is being forced on you by an external environment,
+if the requirement is forced on you by an external environment, such as in a
-and you are sure there is no chance of it being run concurrently (e.g. you are
+Jupyter_ notebook. If you are sure there is no chance of the code being run
-in a Jupyter_ notebook), then you can disable the warning with the
+concurrently, and you *absolutely* need to run this sync code from an async
-``DJANGO_ALLOW_ASYNC_UNSAFE`` environment variable.
+context, then you can disable the warning by setting the
+``DJANGO_ALLOW_ASYNC_UNSAFE`` environment variable to any value.
 
 .. warning::
 
@@ -147,6 +156,8 @@ in a Jupyter_ notebook), then you can disable the warning with the
 
 If you need to do this from within Python, do that with ``os.environ``::
 
+    import os
+
     os.environ["DJANGO_ALLOW_ASYNC_UNSAFE"] = "true"
 
 .. _Jupyter: https://jupyter.org/
@@ -154,11 +165,11 @@ If you need to do this from within Python, do that with ``os.environ``::
 Async adapter functions
 =======================
 
-It is necessary to adapt the calling style when calling synchronous code from
+It is necessary to adapt the calling style when calling sync code from an async
-an asynchronous context, or vice-versa. For this there are two adapter
+context, or vice-versa. For this there are two adapter functions, from the
-functions, made available from the ``asgiref.sync`` package:
+``asgiref.sync`` module: :func:`async_to_sync` and :func:`sync_to_async`. They
-:func:`async_to_sync` and :func:`sync_to_async`. They are used to transition
+are used to transition between the calling styles while preserving
-between sync and async calling styles while preserving compatibility.
+compatibility.
 
 These adapter functions are widely used in Django. The `asgiref`_ package
 itself is part of the Django project, and it is automatically installed as a
@@ -171,28 +182,31 @@ dependency when you install Django with ``pip``.
 
 .. function:: async_to_sync(async_function, force_new_loop=False)
 
-Wraps an asynchronous function and returns a synchronous function in its place.
+Takes an async function and returns a sync function that wraps it. Can be used
-Can be used as either a direct wrapper or a decorator::
+as either a direct wrapper or a decorator::
 
     from asgiref.sync import async_to_sync
 
-    sync_function = async_to_sync(async_function)
+    async def get_data(...):
-
-    @async_to_sync
-    async def async_function(...):
         ...
 
-The asynchronous function is run in the event loop for the current thread, if
+    sync_get_data = async_to_sync(get_data)
-one is present. If there is no current event loop, a new event loop is spun up
+
-specifically for the async function and shut down again once it completes. In
+    @async_to_sync
-either situation, the async function will execute on a different thread to the
+    async def get_other_data(...):
-calling code.
+        ...
+
+The async function is run in the event loop for the current thread, if one is
+present. If there is no current event loop, a new event loop is spun up
+specifically for the single async invocation and shut down again once it
+completes. In either situation, the async function will execute on a different
+thread to the calling code.
 
 Threadlocals and contextvars values are preserved across the boundary in both
 directions.
 
 :func:`async_to_sync` is essentially a more powerful version of the
-:py:func:`asyncio.run` function available in Python's standard library. As well
+:py:func:`asyncio.run` function in Python's standard library. As well
 as ensuring threadlocals work, it also enables the ``thread_sensitive`` mode of
 :func:`sync_to_async` when that wrapper is used below it.
 
@@ -201,8 +215,8 @@ as ensuring threadlocals work, it also enables the ``thread_sensitive`` mode of
 
 .. function:: sync_to_async(sync_function, thread_sensitive=False)
 
-Wraps a synchronous function and returns an asynchronous (awaitable) function
+Takes a sync function and returns an async function that wraps it. Can be used
-in its place. Can be used as either a direct wrapper or a decorator::
+as either a direct wrapper or a decorator::
 
     from asgiref.sync import sync_to_async
 
@@ -220,33 +234,32 @@ in its place. Can be used as either a direct wrapper or a decorator::
 Threadlocals and contextvars values are preserved across the boundary in both
 directions.
 
-Synchronous functions tend to be written assuming they all run in the main
+Sync functions tend to be written assuming they all run in the main
 thread, so :func:`sync_to_async` has two threading modes:
 
-* ``thread_sensitive=False`` (the default): the synchronous function will run
+* ``thread_sensitive=False`` (the default): the sync function will run in a
-  in a brand new thread which is then closed once it completes.
+  brand new thread which is then closed once the invocation completes.
 
-* ``thread_sensitive=True``: the synchronous function will run in the same
+* ``thread_sensitive=True``: the sync function will run in the same thread as
-  thread as all other ``thread_sensitive`` functions, and this will be the main
+  all other ``thread_sensitive`` functions. This will be the main thread, if
-  thread, if the main thread is synchronous and you are using the
+  the main thread is synchronous and you are using the :func:`async_to_sync`
-  :func:`async_to_sync` wrapper.
+  wrapper.
 
 Thread-sensitive mode is quite special, and does a lot of work to run all
 functions in the same thread. Note, though, that it *relies on usage of*
 :func:`async_to_sync` *above it in the stack* to correctly run things on the
-main thread. If you use ``asyncio.run()`` (or other options instead), it will
+main thread. If you use ``asyncio.run()`` or similar, it will fall back to
-fall back to just running thread-sensitive functions in a single, shared thread
+running thread-sensitive functions in a single, shared thread, but this will
-(but not the main thread).
+not be the main thread.
 
 The reason this is needed in Django is that many libraries, specifically
 database adapters, require that they are accessed in the same thread that they
-were created in, and a lot of existing Django code assumes it all runs in the
+were created in. Also a lot of existing Django code assumes it all runs in the
-same thread (e.g. middleware adding things to a request for later use by a
+same thread, e.g. middleware adding things to a request for later use in views.
-view).
 
 Rather than introduce potential compatibility issues with this code, we instead
-opted to add this mode so that all existing Django synchronous code runs in the
+opted to add this mode so that all existing Django sync code runs in the same
-same thread and thus is fully compatible with asynchronous mode. Note, that
+thread and thus is fully compatible with async mode. Note that sync code will
-synchronous code will always be in a *different* thread to any async code that
+always be in a *different* thread to any async code that is calling it, so you
-is calling it, so you should avoid passing raw database handles or other
+should avoid passing raw database handles or other thread-sensitive references
-thread-sensitive references around in any new code you write.
+around.

docs/topics/http/middleware.txt

@@ -308,10 +308,10 @@ on your middleware factory function or class:
   asynchronous requests. Defaults to ``False``.
 
 If your middleware has both ``sync_capable = True`` and
-``async_capable = True``, then Django will pass it the request in whatever form
+``async_capable = True``, then Django will pass it the request without
-it is currently in. You can work out what type of request you have by seeing
+converting it. In this case, you can work out if your middleware will receive
-if the ``get_response`` object you are passed is a coroutine function or not
+async requests by checking if the ``get_response`` object you are passed is a
-(using :py:func:`asyncio.iscoroutinefunction`).
+coroutine function, using :py:func:`asyncio.iscoroutinefunction`.
 
 The ``django.utils.decorators`` module contains
 :func:`~django.utils.decorators.sync_only_middleware`,
@@ -328,8 +328,7 @@ methods, if they are provided, should also be adapted to match the sync/async
 mode. However, Django will individually adapt them as required if you do not,
 at an additional performance penalty.
 
-Here's an example of how to detect and adapt your middleware if it supports
+Here's an example of how to create a middleware function that supports both::
-both::
 
     import asyncio
     from django.utils.decorators import sync_and_async_middleware

docs/topics/http/views.txt

@@ -205,25 +205,26 @@ in a test view. For example::
 
 .. _async-views:
 
-Asynchronous views
+Async views
-==================
+===========
 
 .. versionadded:: 3.1
 
 As well as being synchronous functions, views can also be asynchronous
-functions (``async def``). Django will automatically detect these and run them
+("async") functions, normally defined using Python's ``async def`` syntax.
-in an asynchronous context. You will need to be using an asynchronous (ASGI)
+Django will automatically detect these and run them in an async context.
-server to get the full power of them, however.
+However, you will need to use an async server based on ASGI to get their
+performance benefits.
 
-Here's an example of an asynchronous view::
+Here's an example of an async view::
 
-    from django.http import HttpResponse
     import datetime
+    from django.http import HttpResponse
 
     async def current_datetime(request):
         now = datetime.datetime.now()
         html = '<html><body>It is now %s.</body></html>' % now
         return HttpResponse(html)
 
-You can read more about Django's asynchronous support, and how to best use
+You can read more about Django's async support, and how to best use async
-asynchronous views, in :doc:`/topics/async`.
+views, in :doc:`/topics/async`.

docs/topics/testing/tools.txt

@@ -1808,7 +1808,7 @@ creates.
 
             @mock.patch(...)
             @async_to_sync
-            def test_my_thing(self):
+            async def test_my_thing(self):
                 ...
 
 .. _topics-testing-email: