Add optional socket calls returning a Future. Some TBD rearrangements.

pep-3156.txt

@@ -157,6 +157,13 @@ A conforming event loop object has the following methods:
   - No more registered file descriptors.  It is up to the registering
     party to unregister a file descriptor when it is closed.
 
+- TBD: Do we need an API for stopping the event loop, given that we
+  have the termination condition?  Is the termination condition
+  compatible with other frameworks?
+
+- TBD: Do we need an API to run the event loop for a little while
+  (e.g.  a single iteration)?  If so, exactly what should it do?
+
 - ``call_later(when, callback, *args)``.  Arrange for
   ``callback(*args)`` to be called approximately ``when`` seconds in
   the future, once, unless canceled.  As usual in Python, ``when`` may
@@ -176,9 +183,15 @@ A conforming event loop object has the following methods:
   ``ev.call_soon_threadsafe(ev.call_later, when, callback, *args)``.)
 
 The following methods for registering callbacks for file descriptors
-are optional.  The default implementation provides them but the user
-normally doesn't use these directly -- they are used by the transport
-implementations exclusively:
+are optional.  If they are not implemented, accessing the method
+(without calling it) returns AttributeError.  The default
+implementation provides them but the user normally doesn't use these
+directly -- they are used by the transport implementations
+exclusively.  Also, on Windows these may be present or not depending
+on whether a select-based or IOCP-based event loop is used.  These
+take integer file descriptors only, not objects with a fileno()
+method.  The file descriptor should represent something pollable --
+i.e. no disk files.
 
 - ``add_reader(fd, callback, *args)``.  Arrange for
   ``callback(*args)`` to be called whenever file descriptor ``fd`` is
@@ -201,12 +214,41 @@ implementations exclusively:
 - ``remove_writer(fd)``.  This is to ``add_writer()`` as
   ``remove_reader()`` is to ``add_reader()``.
 
+The following methods for doing async I/O on sockets are optional.
+They are alternative to the previous set of optional methods, intended
+for transport implementations on Windows using IOCP (if the event loop
+supports it).  The socket argument has to be a non-blocking socket.
+
+- ``sock_recv(sock, n)``.  Receive up to ``n`` bytes from socket
+  ``sock``.  Returns a ``Future`` whose result on success will be a
+  bytes object on success.
+
+- ``sock_sendall(sock, data)``.  Send bytes ``data`` to the socket
+  ``sock``.  Returns a ``Future`` whose result on success will be
+  ``None``.  (TBD: Is it better to emulate ``sendall()`` or ``send()``
+  semantics?)
+
+- ``sock_connect(sock, address)``.  Connect to the given address.
+  Returns a ``Future`` whose result on success will be ``None``.
+
+- ``sock_accept(sock)``.  Accept a connection from a socket.  The
+  socket must be in listening mode and bound to an address.  Returns a
+  ``Future`` whose result on success will be a tuple ``(conn, peer)``
+  where ``conn`` is a connected non-blocking socket and ``peer`` is
+  the peer address.
+
+Other TBD:
+
 - TBD: A method to submit a call to a PEP 3148 executor.  Or a method
   to wait for a PEP 3148 Future.  Or both.
 
 - TBD: Methods that return ``Futures``, in particular to make a
   connection and to set up a listener.
 
+- TBD: Do we need introspection APIs?  E.g. asking for the read
+  callback given a file descriptor.  Or when the next scheduled call
+  is.  Or the list of file descriptors registered with callbacks.
+
 Callback Sequencing
 -------------------
 
@@ -218,7 +260,7 @@ in the order in which they are registered.  For example::
 
 guarantees that ``foo()`` is called before ``bar()``.
 
-If ``call_soon()`` is used, this guarantee is even true if the system
+If ``call_soon()`` is used, this guarantee is true even if the system
 clock were to run backwards.  This is also the case for
 ``call_later(0, callback, *args)``.  However, if ``call_later()`` is
 used with a nonzero ``when`` argument, all bets are off if the system
@@ -242,6 +284,8 @@ The DelayedCall Class
 TBD.  (Only one method, ``cancel()``, and a read-only property,
 ``canceled``.  Perhaps also ``callback`` and ``args`` properties.)
 
+TBD: Find a better name?
+
 Futures
 -------
 
@@ -292,16 +336,6 @@ policy.)
 Open Issues
 ===========
 
-- What have I missed that hasn't been marked with TBD yet?
-
-- A better name for ``DelayedCall`` (I really don't like adjectives. :-)
-
-- Do we need an API for stopping the event loop, given that we have
-  the termination condition?  Is the termination condition compatible
-  with other frameworks?
-
-- Do we need an API to run the event loop for a little while?
-
 - Should we have ``future.add_callback(callback, *args)``, using the
   convention from the section "Callback Style" above, or should we
   stick with the PEP 3148 specification of
@@ -310,8 +344,18 @@ Open Issues
   name since add_done_callback() does not guarantee that the callback
   will be called in the right context.)
 
-- Do we need introspection APIs?  E.g. asking for the read callback
-  given a file descriptor.
+- Returning a Future is relatively expensive, and it is quite possible
+  that some types of calls _usually_ complete immediately
+  (e.g. writing small amounts of data to a socket).  A trick used by
+  Richard Oudkerk in the tulip project's proactor branch makes calls
+  like recv() either return a regular result or _raise_ a Future.  The
+  caller (likely a transport) must then write code like this::
+
+    try:
+      res = ev.sock_recv(sock, 8192)
+    except Future as f:
+      yield from sch.block_future(f)
+      res = f.result()
 
 
 Acknowledgments