Give AwakableList's wake-up method the old state in addition to the new state.

mojo/edk/system/local_message_pipe_endpoint.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "mojo/edk/system/local_message_pipe_endpoint.h"
 
 #include <string.h>
 
 #include <utility>
 
@@ skipping 21 matching lines @@
 
 bool LocalMessagePipeEndpoint::OnPeerClose() {
   DCHECK(is_open_);
   DCHECK(is_peer_open_);
 
   HandleSignalsState old_state = GetHandleSignalsState();
   is_peer_open_ = false;
   HandleSignalsState new_state = GetHandleSignalsState();
 
   if (!new_state.equals(old_state))
-    awakable_list_.AwakeForStateChange(new_state);
+    awakable_list_.OnStateChange(old_state, new_state);
 
   return true;
 }
 
 void LocalMessagePipeEndpoint::EnqueueMessage(
     std::unique_ptr<MessageInTransit> message) {
   DCHECK(is_open_);
   DCHECK(is_peer_open_);
 
-  bool was_empty = message_queue_.IsEmpty();
+  HandleSignalsState old_state = GetHandleSignalsState();
   message_queue_.AddMessage(std::move(message));
-  if (was_empty)
-    awakable_list_.AwakeForStateChange(GetHandleSignalsState());
+  HandleSignalsState new_state = GetHandleSignalsState();
+
+  if (!new_state.equals(old_state))
+    awakable_list_.OnStateChange(old_state, new_state);
 }
 
 void LocalMessagePipeEndpoint::Close() {
   DCHECK(is_open_);
   is_open_ = false;
   message_queue_.Clear();
 }
 
 void LocalMessagePipeEndpoint::CancelAllState() {
   DCHECK(is_open_);
@@ skipping 42 matching lines @@
       }
     }
   } else {
     if (num_handles)
       *num_handles = 0;
   }
 
   message = nullptr;
 
   if (enough_space || (flags & MOJO_READ_MESSAGE_FLAG_MAY_DISCARD)) {
+    HandleSignalsState old_state = GetHandleSignalsState();
     message_queue_.DiscardMessage();
+    HandleSignalsState new_state = GetHandleSignalsState();
 
-    // Now it's empty, thus no longer readable.
-    if (message_queue_.IsEmpty()) {
-      // It's currently not possible to wait for non-readability, but we should
-      // do the state change anyway.
-      awakable_list_.AwakeForStateChange(GetHandleSignalsState());
-    }
+    if (!new_state.equals(old_state))
+      awakable_list_.OnStateChange(old_state, new_state);
   }
 
   if (!enough_space)
     return MOJO_RESULT_RESOURCE_EXHAUSTED;
 
   return MOJO_RESULT_OK;
 }
 
 HandleSignalsState LocalMessagePipeEndpoint::GetHandleSignalsState() const {
   HandleSignalsState rv;
@@ skipping 52 matching lines @@
     uint64_t context,
     HandleSignalsState* signals_state) {
   DCHECK(is_open_);
   awakable_list_.RemoveWithContext(awakable, context);
   if (signals_state)
     *signals_state = GetHandleSignalsState();
 }
 
 }  // namespace system
 }  // namespace mojo