[Python-checkins] peps: Allow Handlers as callbacks. Add EventLoop.close().

[guido.van.rossum]

http://hg.python.org/peps/rev/d30c3d0eeea2
changeset:   4661:d30c3d0eeea2
user:        Guido van Rossum <guido at python.org>
date:        Tue Jan 08 19:39:28 2013 -0800
summary:
  Allow Handlers as callbacks. Add EventLoop.close().

files:
  pep-3156.txt |  62 +++++++++++++++++++++++----------------
  1 files changed, 37 insertions(+), 25 deletions(-)


diff --git a/pep-3156.txt b/pep-3156.txt
--- a/pep-3156.txt
+++ b/pep-3156.txt
@@ -148,10 +148,18 @@
 Event Loop Interface
 --------------------
 
-(A note about times: as usual in Python, all timeouts, intervals and
+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()``.)
+default implementation uses ``time.monotonic()``.
+
+A note about callbacks and Handlers: any function that takes a
+callback and a variable number of arguments for it can also be given a
+Handler object instead of the callback.  Then no arguments should be
+given, and the Handler should represent an immediate callback (as
+returned from ``call_soon()``), not a delayed callback (as returned
+from ``call_later()``).  If the Handler is already cancelled, the
+call is a no-op.
 
 A conforming event loop object has the following methods:
 
@@ -173,15 +181,6 @@
 
   TBD: How many variants of this do we really need?
 
-- ``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.
-
-  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_forever()``.  Runs the event loop until ``stop()`` is called.
 
 - ``run_until_complete(future, timeout=None)``.  Runs the event loop
@@ -205,6 +204,20 @@
   ``call_soon()``, causing an infinite loop, ``run_once()`` should
   still return.
 
+- ``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.
+
+  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.
+
+- ``close()``.  Closes the event loop, releasing any resources it may
+  hold, such as the file descriptor used by ``epoll()`` or
+  ``kqueue()``.  This should not be called while the event loop is
+  running.  It may be called multiple times.
+
 - ``call_later(delay, callback, *args)``.  Arrange for
   ``callback(*args)`` to be called approximately ``delay`` seconds in
   the future, once, unless cancelled.  Returns
@@ -232,24 +245,25 @@
 - ``add_signal_handler(sig, callback, *args).  Whenever signal ``sig``
   is received, arrange for ``callback(*args)`` to be called.  Returns
   a ``Handler`` which can be used to cancel the signal callback.
+  (Cancelling the handler causes ``remove_signal_handler()`` to be
+  called the next time the signal arrives.  Explicitly calling
+  ``remove_signal_handler()`` is preferred.)
   Specifying another callback for the same signal replaces the
   previous handler (only one handler can be active per signal).  The
   ``sig`` must be a valid sigal number defined in the ``signal``
   module.  If the signal cannot be handled this raises an exception:
-  ValueError if it is not a valid signal or if it is an uncatchable
-  signale (e.g. ``SIGKILL``), RuntimeError if this particular event
+  ``ValueError`` if it is not a valid signal or if it is an uncatchable
+  signale (e.g. ``SIGKILL``), ``RuntimeError`` if this particular event
   loop instance cannot handle signals (since signals are global per
   process, only an event loop associated with the main thread can
   handle signals).
 
 - ``remove_signal_handler(sig)``.  Removes the handler for signal
   ``sig``, if one is set.  Raises the same exceptions as
-  ``add_signal_handler()``.
-
-- TBD: A way to register a callback that is already wrapped in a
-  ``Handler``.  Maybe ``call_soon()`` could just check
-  ``isinstance(callback, Handler)``?  It should silently skip
-  a cancelled callback.
+  ``add_signal_handler()`` (except that it may return ``False``
+  instead raising ``RuntimeError`` for uncatchable signals).  Returns
+  ``True``e\ if a handler was removed successfully, ``False`` if no
+  handler was set.
 
 Some methods in the standard conforming interface return Futures:
 
@@ -257,15 +271,13 @@
   instance of ``concurrent.futures.Future``) and returns a Future
   compatible with the event loop (i.e., a ``tulip.Future`` instance).
 
-- ``run_in_executor(executor, function, *args)``.  Arrange to call
-  ``function(*args)`` in an executor (see PEP 3148).  Returns a Future
+- ``run_in_executor(executor, callback, *args)``.  Arrange to call
+  ``callback(*args)`` in an executor (see PEP 3148).  Returns a Future
   whose result on success is the return value that call.  This is
-  equivalent to ``wrap_future(executor.submit(function, *args))``.  If
+  equivalent to ``wrap_future(executor.submit(callback, *args))``.  If
   ``executor`` is ``None``, a default ``ThreadPoolExecutor`` with 5
   threads is used.  (TBD: Should the default executor be shared
-  between different event loops?  Should we even have a default
-  executor?  Should be be able to set its thread count?  Shoul we even
-  have this method?)
+  between different event loops?)
 
 - ``set_default_executor(executor)``.  Set the default executor used
   by ``run_in_executor()``.

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