EventLoop: add run_until_complete method (bug 591760)

This emulates the asyncio.AbstractEventLoop.run_until_complete(future)
interface, which will make it possible to reduce latency in situations
where it is desirable for a loop to exit at the earliest opportunity.

The most tangible benefit of this change is that it provides a
migration path to asyncio, which will allow us to rely on a standard
library instead of our own internal event loop implementation.

In order to migrate to asyncio, more work is planned:

* Migrate all internal use of the EventLoop.iteration method to the new
run_until_complete(future) method, and remove the EventLoop.iteration
method (or make it private as long as it's needed to implement
run_until_complete for older python versions).

* Implement all EventLoop methods using asyncio.AbstractEventLoop
methods (but keep existing implementations for use with older python).

X-Gentoo-bug: 591760
X-Gentoo-bug-url: https://bugs.gentoo.org/show_bug.cgi?id=591760
Acked-by: Alexander Berntsen <bernalex@gentoo.org>

pym/portage/tests/ebuild/test_ipc_daemon.py

@@ -1,4 +1,4 @@
-# Copyright 2010-2015 Gentoo Foundation
+# Copyright 2010-2016 Gentoo Foundation
 # Distributed under the terms of the GNU General Public License v2
 
 import tempfile
@@ -16,6 +16,7 @@
 from portage.util._async.ForkProcess import ForkProcess
 from portage.util._async.TaskScheduler import TaskScheduler
 from portage.util._eventloop.global_event_loop import global_event_loop
+from portage.util.futures.futures import Future
 from _emerge.SpawnProcess import SpawnProcess
 from _emerge.EbuildBuildDir import EbuildBuildDir
 from _emerge.EbuildIpcDaemon import EbuildIpcDaemon
@@ -140,19 +141,23 @@ def exit_command_callback():
 				build_dir.unlock()
 			shutil.rmtree(tmpdir)
 
-	def _timeout_callback(self):
-		self._timed_out = True
+	def _timeout_callback(self, task_scheduler):
+		task_scheduler.cancel()
+		self._exit_callback(task_scheduler)
+
+	def _exit_callback(self, task_scheduler):
+		if not self._run_done.done():
+			self._run_done.set_result(True)
 
 	def _run(self, event_loop, task_scheduler, timeout):
-		self._timed_out = False
-		timeout_id = event_loop.timeout_add(timeout, self._timeout_callback)
+		self._run_done = Future()
+		timeout_id = event_loop.timeout_add(timeout,
+			self._timeout_callback, task_scheduler)
+		task_scheduler.addExitListener(self._exit_callback)
 
 		try:
 			task_scheduler.start()
-			while not self._timed_out and task_scheduler.poll() is None:
-				event_loop.iteration()
-			if self._timed_out:
-				task_scheduler.cancel()
+			event_loop.run_until_complete(self._run_done)
 			task_scheduler.wait()
 		finally:
 			event_loop.source_remove(timeout_id)

pym/portage/util/_eventloop/EventLoop.py

@@ -1,4 +1,4 @@
-# Copyright 1999-2014 Gentoo Foundation
+# Copyright 1999-2016 Gentoo Foundation
 # Distributed under the terms of the GNU General Public License v2
 
 from __future__ import division
@@ -577,6 +577,21 @@ def source_remove(self, reg_id):
 		del self._poll_event_handlers[f]
 		return True
 
+	def run_until_complete(self, future):
+		"""
+		Run until the Future is done.
+
+		@type future: asyncio.Future
+		@param future: a Future to wait for
+		@rtype: object
+		@return: the Future's result
+		@raise: the Future's exception
+		"""
+		while not future.done():
+			self.iteration()
+
+		return future.result()
+
 _can_poll_device = None
 
 def can_poll_device():