Mojo: Armed Watchers

mojo/public/cpp/bindings/lib/connector.cc

Index: mojo/public/cpp/bindings/lib/connector.cc
diff --git a/mojo/public/cpp/bindings/lib/connector.cc b/mojo/public/cpp/bindings/lib/connector.cc
index 4426defa934cd0362ecc2eec712730a55dbf04a9..4b029abc9902b18a6d16f11eb438c4e45b946368 100644
--- a/mojo/public/cpp/bindings/lib/connector.cc
+++ b/mojo/public/cpp/bindings/lib/connector.cc
@@ -188,6 +188,12 @@ void Connector::SetWatcherHeapProfilerTag(const char* tag) {
   }
 }
 
+void Connector::EnableNestedDispatch(bool enabled) {
+  nested_dispatch_enabled_ = enabled;
+  handle_watcher_.reset();
+  WaitToReadMore();
+}
+
 void Connector::OnWatcherHandleReady(MojoResult result) {
   OnHandleReadyInternal(result);
 }
@@ -211,6 +217,7 @@ void Connector::OnHandleReadyInternal(MojoResult result) {
     HandleError(result != MOJO_RESULT_FAILED_PRECONDITION, false);
     return;
   }
+
   ReadAllAvailableMessages();
   // At this point, this object might have been deleted. Return.
 }
@@ -219,10 +226,11 @@ void Connector::WaitToReadMore() {
   CHECK(!paused_);
   DCHECK(!handle_watcher_);
 
-  handle_watcher_.reset(new Watcher(FROM_HERE, task_runner_));
+  handle_watcher_.reset(new SimpleWatcher(
+      FROM_HERE, SimpleWatcher::ArmingPolicy::MANUAL, task_runner_));
   if (heap_profiler_tag_)
     handle_watcher_->set_heap_profiler_tag(heap_profiler_tag_);
-  MojoResult rv = handle_watcher_->Start(
+  MojoResult rv = handle_watcher_->Watch(
       message_pipe_.get(), MOJO_HANDLE_SIGNAL_READABLE,
       base::Bind(&Connector::OnWatcherHandleReady, base::Unretained(this)));
 
@@ -232,6 +240,8 @@ void Connector::WaitToReadMore() {
     task_runner_->PostTask(
         FROM_HERE,
         base::Bind(&Connector::OnWatcherHandleReady, weak_self_, rv));
+  } else {
+    handle_watcher_->ArmOrNotify();
   }
 
   if (allow_woken_up_by_others_) {
@@ -253,6 +263,13 @@ bool Connector::ReadSingleMessage(MojoResult* read_result) {
   const MojoResult rv = ReadMessage(message_pipe_.get(), &message);
   *read_result = rv;
 
+  if (nested_dispatch_enabled_) {
+    // When supporting nested dispatch, we have to rearm the Watcher immediately
+    // after reading each message (i.e. before dispatch) to ensure that the next
+    // inbound message can trigger OnHandleReady on the nested loop.
+    handle_watcher_->ArmOrNotify();
+  }
+
   if (rv == MOJO_RESULT_OK) {
     receiver_result =
         incoming_receiver_ && incoming_receiver_->Accept(&message);
@@ -278,19 +295,36 @@ bool Connector::ReadSingleMessage(MojoResult* read_result) {
 
 void Connector::ReadAllAvailableMessages() {
   while (!error_) {
+    base::WeakPtr<Connector> weak_self = weak_self_;
     MojoResult rv;
 
-    if (!ReadSingleMessage(&rv)) {
-      // Return immediately without touching any members. |this| may have been
-      // destroyed.
+    // May delete |this.|
+    if (!ReadSingleMessage(&rv))
       return;
-    }
 
-    if (paused_)
+    if (!weak_self || paused_)
       return;
 
-    if (rv == MOJO_RESULT_SHOULD_WAIT)
-      break;
+    DCHECK(rv == MOJO_RESULT_OK || rv == MOJO_RESULT_SHOULD_WAIT);
+
+    if (rv == MOJO_RESULT_SHOULD_WAIT) {
+      // Attempt to re-arm the Watcher.
+      MojoResult ready_result;
+      MojoResult rv = handle_watcher_->Arm(&ready_result);

[yzshen1, 2017/03/11 00:44:58]

Please consider using a different name, it hides |rv| of the outer scope.

[Ken Rockot(use gerrit already), 2017/03/12 22:24:13]

Done

+      if (rv == MOJO_RESULT_OK)
+        return;
+
+      // The watcher is already ready to notify again.
+      DCHECK_EQ(MOJO_RESULT_FAILED_PRECONDITION, rv);
+
+      if (ready_result == MOJO_RESULT_FAILED_PRECONDITION) {
+        HandleError(false, false);
+        return;
+      }
+
+      // There's more to read now, so we'll just keep looping.
+      DCHECK_EQ(MOJO_RESULT_OK, ready_result);
+    }
   }
 }