Add base::RunLoop and update ui_test_utils to use it to reduce flakiness

base/message_loop.cc

Index: base/message_loop.cc
diff --git a/base/message_loop.cc b/base/message_loop.cc
index a207659a4a922203a2e3850bbcdde4b1425dd21d..db3a3e6f388c3b7f052951641db6dd3f97194a10 100644
--- a/base/message_loop.cc
+++ b/base/message_loop.cc
@@ -303,17 +303,25 @@ void MessageLoop::PostNonNestableDelayedTask(
 }
 
 void MessageLoop::Run() {
-  AutoRunState save_state(this);
+  AutoRunState save_state(this, NULL);
+  RunHandler();
+}
+
+void MessageLoop::RunWithID(const RunID& run_id) {
+  DCHECK(run_id.get() && !run_id->used_);
+  AutoRunState save_state(this, run_id);
+  if (run_id->quit_now_received_)

[jar (doing other things), 2012/06/18 19:43:21]

If you want to make the DCHECK in line 311 more valuable, you should add to this
clause:
run_id->used_ = true;

[jbates, 2012/06/18 23:14:03]

It's done by the AutoRunState constructor. I moved the DCHECK there to be more
clear.

+    return;
   RunHandler();
 }
 
 void MessageLoop::RunAllPending() {
-  AutoRunState save_state(this);
+  AutoRunState save_state(this, NULL);
   state_->quit_received = true;  // Means run until we would otherwise block.
   RunHandler();
 }
 
-void MessageLoop::Quit() {
+void MessageLoop::QuitWhenIdle() {
   DCHECK_EQ(this, current());
   if (state_) {
     state_->quit_received = true;
@@ -331,13 +339,51 @@ void MessageLoop::QuitNow() {
   }
 }
 
-static void QuitCurrent() {
-  MessageLoop::current()->Quit();
+void MessageLoop::QuitNowWithID(const RunID& run_id) {
+  DCHECK_EQ(this, current());
+  if (!state_)
+    return;
+  // If the state_ pointer matches that of the RunIDObject, we're at the same
+  // Run scope, so quit now.
+  if (state_ == run_id->run_state_)
+    QuitNow();
+
+  // Set quit_now_received_ so that the corresponding Run scope is quit as soon
+  // as it is returned to. It's also possible that the corresponding Run has not
+  // begun; in that case, this will cause the Run to immediately return.

[jar (doing other things), 2012/06/18 19:43:21]

Is the case of calling quit before the RunWithId() useful?  IF so, this
justifies the separate bool.

Does this let us run exactly one task in a message loop? Is there another
scenario for this?

[jbates, 2012/06/18 23:14:03]

Explained in response to your other comment in message_loop.h. This feature
should allow some simplification of test code that is currently responsible for
tracking run/quit states. I added some new tests to verify behavior when
QuitWithID is used before, during and after RunWithID.

+  run_id->quit_now_received_ = true;
+}
+
+static void QuitCurrentWhenIdle() {
+  MessageLoop::current()->QuitWhenIdle();
+}
+
+static void QuitCurrentNow() {
+  MessageLoop::current()->QuitNow();
+}
+
+static void QuitCurrentNowWithID(const MessageLoop::RunID& run_id) {
+  MessageLoop::current()->QuitNowWithID(run_id);
+}
+
+// static
+base::Closure MessageLoop::QuitWhenIdleClosure() {
+  return base::Bind(&QuitCurrentWhenIdle);
+}
+
+// static
+base::Closure MessageLoop::QuitNowClosure() {
+  return base::Bind(&QuitCurrentNow);
 }
 
 // static
-base::Closure MessageLoop::QuitClosure() {
-  return base::Bind(&QuitCurrent);
+base::Closure MessageLoop::QuitNowWithIDClosure(
+    const RunID& run_id) {
+  return base::Bind(&QuitCurrentNowWithID, run_id);
+}
+
+MessageLoop::RunID MessageLoop::GetRunID() {
+  return new RunIDObject();
 }
 
 void MessageLoop::SetNestableTasksAllowed(bool allowed) {
@@ -716,9 +762,19 @@ void MessageLoop::ReleaseSoonInternal(
 }
 
 //------------------------------------------------------------------------------
+// MessageLoop::RunState
+
+MessageLoop::RunState::RunState() {
+}
+
+MessageLoop::RunState::~RunState() {
+}
+
+//------------------------------------------------------------------------------
 // MessageLoop::AutoRunState
 
-MessageLoop::AutoRunState::AutoRunState(MessageLoop* loop) : loop_(loop) {
+MessageLoop::AutoRunState::AutoRunState(MessageLoop* loop, const RunID& run_id)
+    : loop_(loop) {
   // Make the loop reference us.
   previous_state_ = loop_->state_;
   if (previous_state_) {
@@ -728,6 +784,12 @@ MessageLoop::AutoRunState::AutoRunState(MessageLoop* loop) : loop_(loop) {
   }
   loop_->state_ = this;
 
+  if (run_id.get()) {
+    run_state_id = run_id;
+    run_state_id->used_ = true;
+    run_state_id->run_state_ = this;
+  }
+
   // Initialize the other fields:
   quit_received = false;
 #if !defined(OS_MACOSX) && !defined(OS_ANDROID)
@@ -737,6 +799,13 @@ MessageLoop::AutoRunState::AutoRunState(MessageLoop* loop) : loop_(loop) {
 
 MessageLoop::AutoRunState::~AutoRunState() {
   loop_->state_ = previous_state_;
+  if (run_state_id.get()) {
+    // run_state_id->run_state_ points to 'this', so clear it.
+    run_state_id->run_state_ = NULL;
+  }
+  if (previous_state_ && previous_state_->run_state_id.get()
+      && previous_state_->run_state_id->quit_now_received_)
+    MessageLoop::current()->QuitNow();
 }
 
 //------------------------------------------------------------------------------
@@ -765,13 +834,20 @@ void MessageLoopForUI::RemoveObserver(Observer* observer) {
 }
 
 void MessageLoopForUI::RunWithDispatcher(Dispatcher* dispatcher) {
-  AutoRunState save_state(this);
+  AutoRunState save_state(this, NULL);
+  state_->dispatcher = dispatcher;
+  RunHandler();
+}
+
+void MessageLoopForUI::RunWithDispatcher(Dispatcher* dispatcher,
+                                         const RunID& run_id) {
+  AutoRunState save_state(this, run_id);
   state_->dispatcher = dispatcher;
   RunHandler();
 }
 
 void MessageLoopForUI::RunAllPendingWithDispatcher(Dispatcher* dispatcher) {
-  AutoRunState save_state(this);
+  AutoRunState save_state(this, NULL);
   state_->dispatcher = dispatcher;
   state_->quit_received = true;  // Means run until we would otherwise block.
   RunHandler();