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

mojo/edk/system/data_pipe.cc

Index: mojo/edk/system/data_pipe.cc
diff --git a/mojo/edk/system/data_pipe.cc b/mojo/edk/system/data_pipe.cc
index 7167873266e740e66894892897d7a054f6f2e730..cff209af838e2f3bee4ea4cd18e2b57f2b6f31f9 100644
--- a/mojo/edk/system/data_pipe.cc
+++ b/mojo/edk/system/data_pipe.cc
@@ -290,10 +290,8 @@ MojoResult DataPipe::ProducerSetOptions(uint32_t write_threshold_num_bytes) {
   HandleSignalsState old_producer_state =
       impl_->ProducerGetHandleSignalsState();
   producer_write_threshold_num_bytes_ = write_threshold_num_bytes;
-  HandleSignalsState new_producer_state =
-      impl_->ProducerGetHandleSignalsState();
-  if (!new_producer_state.equals(old_producer_state))
-    AwakeProducerAwakablesForStateChangeNoLock(new_producer_state);
+  OnProducerMaybeStateChange(old_producer_state,
+                             impl_->ProducerGetHandleSignalsState());
   return MOJO_RESULT_OK;
 }
 
@@ -328,10 +326,8 @@ MojoResult DataPipe::ProducerWriteData(UserPointer<const void> elements,
       impl_->ConsumerGetHandleSignalsState();
   MojoResult rv = impl_->ProducerWriteData(
       elements, num_bytes, max_num_bytes_to_write, min_num_bytes_to_write);
-  HandleSignalsState new_consumer_state =
-      impl_->ConsumerGetHandleSignalsState();
-  if (!new_consumer_state.equals(old_consumer_state))
-    AwakeConsumerAwakablesForStateChangeNoLock(new_consumer_state);
+  OnConsumerMaybeStateChange(old_consumer_state,
+                             impl_->ConsumerGetHandleSignalsState());
   return rv;
 }
 
@@ -368,6 +364,8 @@ MojoResult DataPipe::ProducerEndWriteData(uint32_t num_bytes_written) {
 
   HandleSignalsState old_consumer_state =
       impl_->ConsumerGetHandleSignalsState();
+  HandleSignalsState old_producer_state =
+      impl_->ProducerGetHandleSignalsState();
   MojoResult rv;
   if (num_bytes_written > producer_two_phase_max_num_bytes_written_ ||
       num_bytes_written % element_num_bytes() != 0) {
@@ -380,14 +378,10 @@ MojoResult DataPipe::ProducerEndWriteData(uint32_t num_bytes_written) {
   DCHECK(!producer_in_two_phase_write_no_lock());
   // If we're now writable, we *became* writable (since we weren't writable
   // during the two-phase write), so awake producer awakables.
-  HandleSignalsState new_producer_state =
-      impl_->ProducerGetHandleSignalsState();
-  if (new_producer_state.satisfies(MOJO_HANDLE_SIGNAL_WRITABLE))
-    AwakeProducerAwakablesForStateChangeNoLock(new_producer_state);
-  HandleSignalsState new_consumer_state =
-      impl_->ConsumerGetHandleSignalsState();
-  if (!new_consumer_state.equals(old_consumer_state))
-    AwakeConsumerAwakablesForStateChangeNoLock(new_consumer_state);
+  OnProducerMaybeStateChange(old_producer_state,
+                             impl_->ProducerGetHandleSignalsState());
+  OnConsumerMaybeStateChange(old_consumer_state,
+                             impl_->ConsumerGetHandleSignalsState());
   return rv;
 }
 
@@ -491,10 +485,8 @@ MojoResult DataPipe::ConsumerSetOptions(uint32_t read_threshold_num_bytes) {
   HandleSignalsState old_consumer_state =
       impl_->ConsumerGetHandleSignalsState();
   consumer_read_threshold_num_bytes_ = read_threshold_num_bytes;
-  HandleSignalsState new_consumer_state =
-      impl_->ConsumerGetHandleSignalsState();
-  if (!new_consumer_state.equals(old_consumer_state))
-    AwakeConsumerAwakablesForStateChangeNoLock(new_consumer_state);
+  OnConsumerMaybeStateChange(old_consumer_state,
+                             impl_->ConsumerGetHandleSignalsState());
   return MOJO_RESULT_OK;
 }
 
@@ -527,10 +519,8 @@ MojoResult DataPipe::ConsumerReadData(UserPointer<void> elements,
       impl_->ProducerGetHandleSignalsState();
   MojoResult rv = impl_->ConsumerReadData(
       elements, num_bytes, max_num_bytes_to_read, min_num_bytes_to_read, peek);
-  HandleSignalsState new_producer_state =
-      impl_->ProducerGetHandleSignalsState();
-  if (!new_producer_state.equals(old_producer_state))
-    AwakeProducerAwakablesForStateChangeNoLock(new_producer_state);
+  OnProducerMaybeStateChange(old_producer_state,
+                             impl_->ProducerGetHandleSignalsState());
   return rv;
 }
 
@@ -556,10 +546,8 @@ MojoResult DataPipe::ConsumerDiscardData(UserPointer<uint32_t> num_bytes,
       impl_->ProducerGetHandleSignalsState();
   MojoResult rv = impl_->ConsumerDiscardData(
       num_bytes, max_num_bytes_to_discard, min_num_bytes_to_discard);
-  HandleSignalsState new_producer_state =
-      impl_->ProducerGetHandleSignalsState();
-  if (!new_producer_state.equals(old_producer_state))
-    AwakeProducerAwakablesForStateChangeNoLock(new_producer_state);
+  OnProducerMaybeStateChange(old_producer_state,
+                             impl_->ProducerGetHandleSignalsState());
   return rv;
 }
 
@@ -613,14 +601,10 @@ MojoResult DataPipe::ConsumerEndReadData(uint32_t num_bytes_read) {
   DCHECK(!consumer_in_two_phase_read_no_lock());
   // If we're now readable, we *became* readable (since we weren't readable
   // during the two-phase read), so awake consumer awakables.
-  HandleSignalsState new_consumer_state =
-      impl_->ConsumerGetHandleSignalsState();
-  if (!new_consumer_state.equals(old_consumer_state))
-    AwakeConsumerAwakablesForStateChangeNoLock(new_consumer_state);
-  HandleSignalsState new_producer_state =
-      impl_->ProducerGetHandleSignalsState();
-  if (!new_producer_state.equals(old_producer_state))
-    AwakeProducerAwakablesForStateChangeNoLock(new_producer_state);
+  OnConsumerMaybeStateChange(old_consumer_state,
+                             impl_->ConsumerGetHandleSignalsState());
+  OnProducerMaybeStateChange(old_producer_state,
+                             impl_->ProducerGetHandleSignalsState());
   return rv;
 }
 
@@ -787,27 +771,31 @@ void DataPipe::SetConsumerClosedNoLock() {
 void DataPipe::ProducerCloseNoLock() {
   mutex_.AssertHeld();
   DCHECK(producer_open_);
+  HandleSignalsState old_consumer_state =
+      impl_->ConsumerGetHandleSignalsState();
   producer_open_ = false;
   if (has_local_producer_no_lock()) {
     ProducerCancelAllStateNoLock();
     producer_awakable_list_.reset();
     impl_->ProducerClose();
-    AwakeConsumerAwakablesForStateChangeNoLock(
-        impl_->ConsumerGetHandleSignalsState());
   }
+  OnConsumerMaybeStateChange(old_consumer_state,
+                             impl_->ConsumerGetHandleSignalsState());
 }
 
 void DataPipe::ConsumerCloseNoLock() {
   mutex_.AssertHeld();
   DCHECK(consumer_open_);
+  HandleSignalsState old_producer_state =
+      impl_->ProducerGetHandleSignalsState();
   consumer_open_ = false;
   if (has_local_consumer_no_lock()) {
     ConsumerCancelAllStateNoLock();
     consumer_awakable_list_.reset();
     impl_->ConsumerClose();
-    AwakeProducerAwakablesForStateChangeNoLock(
-        impl_->ProducerGetHandleSignalsState());
   }
+  OnProducerMaybeStateChange(old_producer_state,
+                             impl_->ProducerGetHandleSignalsState());
 }
 
 bool DataPipe::OnReadMessage(unsigned port, MessageInTransit* message) {
@@ -821,14 +809,10 @@ bool DataPipe::OnReadMessage(unsigned port, MessageInTransit* message) {
 
   bool rv = impl_->OnReadMessage(port, message);
 
-  HandleSignalsState new_producer_state =
-      impl_->ProducerGetHandleSignalsState();
-  if (!new_producer_state.equals(old_producer_state))
-    AwakeProducerAwakablesForStateChangeNoLock(new_producer_state);
-  HandleSignalsState new_consumer_state =
-      impl_->ConsumerGetHandleSignalsState();
-  if (!new_consumer_state.equals(old_consumer_state))
-    AwakeConsumerAwakablesForStateChangeNoLock(new_consumer_state);
+  OnProducerMaybeStateChange(old_producer_state,
+                             impl_->ProducerGetHandleSignalsState());
+  OnConsumerMaybeStateChange(old_consumer_state,
+                             impl_->ConsumerGetHandleSignalsState());
 
   return rv;
 }
@@ -844,30 +828,32 @@ void DataPipe::OnDetachFromChannel(unsigned port) {
 
   impl_->OnDetachFromChannel(port);
 
-  HandleSignalsState new_producer_state =
-      impl_->ProducerGetHandleSignalsState();
-  if (!new_producer_state.equals(old_producer_state))
-    AwakeProducerAwakablesForStateChangeNoLock(new_producer_state);
-  HandleSignalsState new_consumer_state =
-      impl_->ConsumerGetHandleSignalsState();
-  if (!new_consumer_state.equals(old_consumer_state))
-    AwakeConsumerAwakablesForStateChangeNoLock(new_consumer_state);
+  OnProducerMaybeStateChange(old_producer_state,
+                             impl_->ProducerGetHandleSignalsState());
+  OnConsumerMaybeStateChange(old_consumer_state,
+                             impl_->ConsumerGetHandleSignalsState());
 }
 
-void DataPipe::AwakeProducerAwakablesForStateChangeNoLock(
+void DataPipe::OnProducerMaybeStateChange(
+    const HandleSignalsState& old_producer_state,
     const HandleSignalsState& new_producer_state) {
   mutex_.AssertHeld();
-  if (!has_local_producer_no_lock())
-    return;
-  producer_awakable_list_->AwakeForStateChange(new_producer_state);
+  if (!new_producer_state.equals(old_producer_state) &&
+      has_local_producer_no_lock()) {
+    producer_awakable_list_->OnStateChange(old_producer_state,
+                                           new_producer_state);
+  }
 }
 
-void DataPipe::AwakeConsumerAwakablesForStateChangeNoLock(
+void DataPipe::OnConsumerMaybeStateChange(
+    const HandleSignalsState& old_consumer_state,
     const HandleSignalsState& new_consumer_state) {
   mutex_.AssertHeld();
-  if (!has_local_consumer_no_lock())
-    return;
-  consumer_awakable_list_->AwakeForStateChange(new_consumer_state);
+  if (!new_consumer_state.equals(old_consumer_state) &&
+      has_local_consumer_no_lock()) {
+    consumer_awakable_list_->OnStateChange(old_consumer_state,
+                                           new_consumer_state);
+  }
 }
 
 void DataPipe::SetProducerClosed() {