asyncio: sync with Tulip

* Fix _WaitHandleFuture.cancel(): return the result of the parent cancel()
  method.
* _OverlappedFuture.cancel() now clears its reference to the overlapped object.
  Make also the _OverlappedFuture.ov attribute private.
* Check if _WaitHandleFuture completed before unregistering it in the callback.
  Add also _WaitHandleFuture._poll() and repr(_WaitHandleFuture).
* _WaitHandleFuture now unregisters its wait handler if WaitForSingleObject()
  raises an exception.
* _OverlappedFuture.set_exception() now cancels the overlapped operation.

Lib/asyncio/proactor_events.py

@@ -44,13 +44,9 @@ class _ProactorBasePipeTransport(transports._FlowControlMixin,
     def __repr__(self):
         info = [self.__class__.__name__, 'fd=%s' % self._sock.fileno()]
         if self._read_fut is not None:
-            ov = "pending" if self._read_fut.ov.pending else "completed"
-            info.append('read=%s' % ov)
+            info.append('read=%s' % self._read_fut)
         if self._write_fut is not None:
-            if self._write_fut.ov.pending:
-                info.append("write=pending=%s" % self._pending_write)
-            else:
-                info.append("write=completed")
+            info.append("write=%r" % self._write_fut)
         if self._buffer:
             bufsize = len(self._buffer)
             info.append('write_bufsize=%s' % bufsize)

Lib/asyncio/windows_events.py

@@ -40,22 +40,24 @@ class _OverlappedFuture(futures.Future):
         super().__init__(loop=loop)
         if self._source_traceback:
             del self._source_traceback[-1]
-        self.ov = ov
+        self._ov = ov
 
     def __repr__(self):
         info = [self._state.lower()]
-        state = 'pending' if self.ov.pending else 'completed'
-        info.append('overlapped=<%s, %#x>' % (state, self.ov.address))
+        if self._ov is not None:
+            state = 'pending' if self._ov.pending else 'completed'
+            info.append('overlapped=<%s, %#x>' % (state, self._ov.address))
         if self._state == futures._FINISHED:
             info.append(self._format_result())
         if self._callbacks:
             info.append(self._format_callbacks())
         return '<%s %s>' % (self.__class__.__name__, ' '.join(info))
 
-    def cancel(self):
-        if not self.done():
+    def _cancel_overlapped(self):
+        if self._ov is None:
+            return
         try:
-                self.ov.cancel()
+            self._ov.cancel()
         except OSError as exc:
             context = {
                 'message': 'Cancelling an overlapped future failed',
@@ -65,16 +67,42 @@ class _OverlappedFuture(futures.Future):
             if self._source_traceback:
                 context['source_traceback'] = self._source_traceback
             self._loop.call_exception_handler(context)
+        self._ov = None
+
+    def cancel(self):
+        self._cancel_overlapped()
         return super().cancel()
 
+    def set_exception(self, exception):
+        super().set_exception(exception)
+        self._cancel_overlapped()
+
 
 class _WaitHandleFuture(futures.Future):
     """Subclass of Future which represents a wait handle."""
 
-    def __init__(self, wait_handle, *, loop=None):
+    def __init__(self, handle, wait_handle, *, loop=None):
         super().__init__(loop=loop)
+        self._handle = handle
         self._wait_handle = wait_handle
 
+    def _poll(self):
+        # non-blocking wait: use a timeout of 0 millisecond
+        return (_winapi.WaitForSingleObject(self._handle, 0) ==
+                _winapi.WAIT_OBJECT_0)
+
+    def __repr__(self):
+        info = [self._state.lower()]
+        if self._wait_handle:
+            state = 'pending' if self._poll() else 'completed'
+            info.append('wait_handle=<%s, %#x>' % (state, self._wait_handle))
+        info.append('handle=<%#x>' % self._handle)
+        if self._state == futures._FINISHED:
+            info.append(self._format_result())
+        if self._callbacks:
+            info.append(self._format_callbacks())
+        return '<%s %s>' % (self.__class__.__name__, ' '.join(info))
+
     def _unregister(self):
         if self._wait_handle is None:
             return
@@ -88,7 +116,7 @@ class _WaitHandleFuture(futures.Future):
 
     def cancel(self):
         self._unregister()
-        super().cancel()
+        return super().cancel()
 
 
 class PipeServer(object):
@@ -370,18 +398,19 @@ class IocpProactor:
         ov = _overlapped.Overlapped(NULL)
         wh = _overlapped.RegisterWaitWithQueue(
             handle, self._iocp, ov.address, ms)
-        f = _WaitHandleFuture(wh, loop=self._loop)
+        f = _WaitHandleFuture(handle, wh, loop=self._loop)
 
         def finish_wait_for_handle(trans, key, ov):
-            f._unregister()
             # Note that this second wait means that we should only use
             # this with handles types where a successful wait has no
             # effect.  So events or processes are all right, but locks
             # or semaphores are not.  Also note if the handle is
             # signalled and then quickly reset, then we may return
             # False even though we have not timed out.
-            return (_winapi.WaitForSingleObject(handle, 0) ==
-                    _winapi.WAIT_OBJECT_0)
+            try:
+                return f._poll()
+            finally:
+                f._unregister()
 
         self._cache[ov.address] = (f, ov, None, finish_wait_for_handle)
         return f