[Python-checkins] peps: Small tweaks and clarifications.

[guido.van.rossum]

http://hg.python.org/peps/rev/1f95b1f65c8c
changeset:   4623:1f95b1f65c8c
user:        Guido van Rossum <guido at google.com>
date:        Wed Dec 19 19:35:42 2012 -0800
summary:
  Small tweaks and clarifications.

files:
  pep-3156.txt |  75 ++++++++++++++++++++-------------------
  1 files changed, 38 insertions(+), 37 deletions(-)


diff --git a/pep-3156.txt b/pep-3156.txt
--- a/pep-3156.txt
+++ b/pep-3156.txt
@@ -148,66 +148,69 @@
 Event Loop Interface
 --------------------
 
+(A note about times: as usual in Python, all timeouts, intervals and
+delays are measured in seconds, and may be ints or floats.  The
+accuracy and precision of the clock are up to the implementation; the
+default implementation uses ``time.monotonic()``.)
+
 A conforming event loop object has the following methods:
 
-..
-  Look for a better way to format method docs.  PEP 12 doesn't seem to
-  have one.  PEP 418 uses ^^^, which makes sub-headings.  PEP 3148
-  uses a markup which generates rather heavy layout using blockquote,
-  causing a blank line between each method heading and its
-  description.  Also think of adding subheadings for different
-  categories of methods.
-
 - ``run()``.  Runs the event loop until there is nothing left to do.
   This means, in particular:
 
-  - No more calls scheduled with ``call_later()`` (except for canceled
-    calls).
+  - No more calls scheduled with ``call_later()``,
+  ``call_repeatedly()``, ``call_soon()``, or
+  ``call_soon_threadsafe()``, except for canceled calls.
 
   - No more registered file descriptors.  It is up to the registering
     party to unregister a file descriptor when it is closed.
 
-  Note: run() blocks until the termination condition is met.
+  Note: ``run()`` blocks until the termination condition is met,
+  or until ``stop()`` is called.
+
+  Note: if you schedule a call with ``call_repeatedly()``, ``run()``
+  will not exit until you cancel it.
 
 - ``stop()``.  Stops the event loop as soon as it is convenient.  It
   is fine to restart the loop with ``run()`` (or one of its variants)
-  subsequently.  (TBD: How should this interact with ``run_once()``
-  and ``run_until_complete()``?)
+  subsequently.
 
-  Note: How soon exactly is up to the implementation.  It is
-  reasonable to implement this so that ``run()`` simply stops calling
-  ``run_once()`` when this is called.
+  Note: How soon exactly is up to the implementation.  All immediate
+  callbacks that were already scheduled to run before ``stop()`` is
+  called must still be run, but callbacks scheduled after it is called
+  (or scheduled to be run later) will not be run.
 
 - ``run_until_complete(future, timeout=None)``.  Runs the event loop
-  until a Future is done.  If a timeout is given, it waits at most
+  until the Future is done.  If a timeout is given, it waits at most
   that long.  If the Future is done, its result is returned, or its
   exception is raised; if the timeout expires before the Future is
-  done, TimeoutError is raised (but the Future is not cancelled).
-  This cannot be called when the event loop is already running.
+  done, or if ``stop()`` is called, ``TimeoutError`` is raised (but
+  the Future is not cancelled).  This cannot be called when the event
+  loop is already running.
   
   Note: This API is most useful for tests and the like.  It should not
   be used as a substitute for ``yield from future`` or other ways to
   wait for a Future (e.g. registering a done callback).
 
 - ``run_once(timeout=None)``.  Run the event loop for a little while.
-  If a timeout is given, an I/O poll will be given at most that timeout;
-  otherwise, an I/O poll is not constrained in time.
+  If a timeout is given, an I/O poll made will block at most that
+  long; otherwise, an I/O poll is not constrained in time.
 
-  Note: Exactlly what this does is up to the implementation.  One
-  constraint: if a callback immediately schedules itself using
-  ``call_soon()``, ``run_once()`` should still return.
+  Note: Exactlly how much work this does is up to the implementation.
+  One constraint: if a callback immediately schedules itself using
+  ``call_soon()``, causing an infinite loop, ``run_once()`` should
+  still return.
 
 - ``call_later(delay, callback, *args)``.  Arrange for
   ``callback(*args)`` to be called approximately ``delay`` seconds in
-  the future, once, unless canceled.  As usual in Python, ``delay`` may
-  be a floating point number to represent smaller intervals.  Returns
+  the future, once, unless canceled.  Returns
   a ``Handler`` object representing the callback, whose
   ``cancel()`` method can be used to cancel the callback.
 
 - ``call_repeatedly(interval, callback, **args)``.  Like ``call_later()``
   but calls the callback repeatedly, every ``interval`` seconds,
   until the ``Handler`` returned is cancelled.  The first call is in
-  ``interval`` seconds.  May be a float.
+  ``interval`` seconds.
 
 - ``call_soon(callback, *args)``.  Equivalent to ``call_later(0,
   callback, *args)``.
@@ -225,8 +228,6 @@
   ``isinstance(callback, Handler)``?  It should silently skip
   a canceled callback.
 
-- TBD: Repeatable timers.
-
 Some methods in the standard conforming interface return Futures:
 
 - ``wrap_future(future)``.  This takes a PEP 3148 Future (i.e., an
@@ -336,10 +337,8 @@
 
 TBD: What about multiple callbacks per fd?  The current semantics is
 that ``add_reader()/add_writer()`` replace a previously registered
-callback.
-
-TBD: Should ``remove_*()`` return a bool telling is whether it removed
-anything?
+callback.  Change this to raise an exception if a callback is already
+registered.
 
 The following methods for doing async I/O on sockets are optional.
 They are alternative to the previous set of optional methods, intended
@@ -353,7 +352,8 @@
 - ``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?)
+  semantics?  I think ``sendall()`` -- but perhaps it should still
+  be *named* ``send()``?)
 
 - ``sock_connect(sock, address)``.  Connect to the given address.
   Returns a Future whose result on success will be ``None``.
@@ -605,9 +605,10 @@
 
 TBD: Provide flow control the other way -- the transport may need to
 suspend the protocol if the amount of data buffered becomes a burden.
-One option: let the transport call ``protocol.pause()`` and
-``protocol.resume()`` if they exist; if they don't exist, the protocol
-doesn't support flow control.
+Proposal: let the transport call ``protocol.pause()`` and
+``protocol.resume()`` if they exist; if they don't exist, the
+protocol doesn't support flow control.  (Perhaps different names
+to avoid confusion between protocols and transports?)
 
 Protocols
 ---------

-- 
Repository URL: http://hg.python.org/peps