(Merge 3.4) asyncio, tulip issue 196: ProactorIocp._register() now registers

the overlapped in the _cache dictionary, even if we already got the result. We
need to keep a reference to the overlapped object, otherwise the memory may be
reused and GetQueuedCompletionStatus() may use random bytes and behaves badly.

There is still a hack for ConnectNamedPipe(): the overlapped object is not
register into _cache if the overlapped object completed directly.

Log also an error in debug mode in ProactorIocp._loop() if we get an unexpected
event.

Add a protection in ProactorIocp.close() to avoid blocking, even if it should
not happen. I still don't understand exactly why some the completion of some
overlapped objects are not notified.

Lib/asyncio/windows_events.py

@@ -369,7 +369,10 @@ class IocpProactor:
             ov.getresult()
             return pipe
 
-        return self._register(ov, pipe, finish_accept_pipe)
+        # FIXME: Tulip issue 196: why to we neeed register=False?
+        # See also the comment in the _register() method
+        return self._register(ov, pipe, finish_accept_pipe,
+                              register=False)
 
     def connect_pipe(self, address):
         ov = _overlapped.Overlapped(NULL)
@@ -429,17 +432,13 @@ class IocpProactor:
             # to avoid sending notifications to completion port of ops
             # that succeed immediately.
 
-    def _register(self, ov, obj, callback, wait_for_post=False):
+    def _register(self, ov, obj, callback,
+                  wait_for_post=False, register=True):
         # Return a future which will be set with the result of the
         # operation when it completes.  The future's value is actually
         # the value returned by callback().
         f = _OverlappedFuture(ov, loop=self._loop)
-        if ov.pending or wait_for_post:
-            # Register the overlapped operation for later.  Note that
-            # we only store obj to prevent it from being garbage
-            # collected too early.
-            self._cache[ov.address] = (f, ov, obj, callback)
-        else:
+        if not ov.pending and not wait_for_post:
             # The operation has completed, so no need to postpone the
             # work.  We cannot take this short cut if we need the
             # NumberOfBytes, CompletionKey values returned by
@@ -450,6 +449,23 @@ class IocpProactor:
                 f.set_exception(e)
             else:
                 f.set_result(value)
+            # Even if GetOverlappedResult() was called, we have to wait for the
+            # notification of the completion in GetQueuedCompletionStatus().
+            # Register the overlapped operation to keep a reference to the
+            # OVERLAPPED object, otherwise the memory is freed and Windows may
+            # read uninitialized memory.
+            #
+            # For an unknown reason, ConnectNamedPipe() behaves differently:
+            # the completion is not notified by GetOverlappedResult() if we
+            # already called GetOverlappedResult(). For this specific case, we
+            # don't expect notification (register is set to False).
+        else:
+            register = True
+        if register:
+            # Register the overlapped operation for later.  Note that
+            # we only store obj to prevent it from being garbage
+            # collected too early.
+            self._cache[ov.address] = (f, ov, obj, callback)
         return f
 
     def _get_accept_socket(self, family):
@@ -476,6 +492,14 @@ class IocpProactor:
             try:
                 f, ov, obj, callback = self._cache.pop(address)
             except KeyError:
+                if self._loop.get_debug():
+                    self._loop.call_exception_handler({
+                        'message': ('GetQueuedCompletionStatus() returned an '
+                                    'unexpected event'),
+                        'status': ('err=%s transferred=%s key=%#x address=%#x'
+                                   % (err, transferred, key, address)),
+                    })
+
                 # key is either zero, or it is used to return a pipe
                 # handle which should be closed to avoid a leak.
                 if key not in (0, _overlapped.INVALID_HANDLE_VALUE):
@@ -483,15 +507,11 @@ class IocpProactor:
                 ms = 0
                 continue
 
-            if ov.pending:
-                # False alarm: the overlapped operation is not completed.
-                # FIXME: why do we get false alarms?
-                self._cache[address] = (f, ov, obj, callback)
-                continue
-
             if obj in self._stopped_serving:
                 f.cancel()
-            elif not f.cancelled():
+            # Don't call the callback if _register() already read the result or
+            # if the overlapped has been cancelled
+            elif not f.done():
                 try:
                     value = callback(transferred, key, ov)
                 except OSError as e:
@@ -516,6 +536,9 @@ class IocpProactor:
                 # queues a task to Windows' thread pool.  This cannot
                 # be cancelled, so just forget it.
                 del self._cache[address]
+            # FIXME: Tulip issue 196: remove this case, it should not happen
+            elif fut.done() and not fut.cancelled():
+                del self._cache[address]
             else:
                 try:
                     fut.cancel()