Make HandleWatcher watch on the same thread if the thread is running a MessagePumpMojo.

mojo/common/handle_watcher.cc

Index: mojo/common/handle_watcher.cc
diff --git a/mojo/common/handle_watcher.cc b/mojo/common/handle_watcher.cc
index 33bb0bdeaa7daae80a0c74e46b688052b1164c9c..eeb3e043b4e3d7f41105d408f1d16fbfd2730fec 100644
--- a/mojo/common/handle_watcher.cc
+++ b/mojo/common/handle_watcher.cc
@@ -9,6 +9,8 @@
 #include "base/atomic_sequence_num.h"
 #include "base/bind.h"
 #include "base/lazy_instance.h"
+#include "base/logging.h"
+#include "base/macros.h"
 #include "base/memory/singleton.h"
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop/message_loop.h"
@@ -31,14 +33,6 @@ namespace {
 
 const char kWatcherThreadName[] = "handle-watcher-thread";
 
-// TODO(sky): this should be unnecessary once MessageLoop has been refactored.
-MessagePumpMojo* message_pump_mojo = NULL;
-
-scoped_ptr<base::MessagePump> CreateMessagePumpMojo() {
-  message_pump_mojo = new MessagePumpMojo;
-  return scoped_ptr<base::MessagePump>(message_pump_mojo).Pass();
-}
-
 base::TimeTicks MojoDeadlineToTimeTicks(MojoDeadline deadline) {
   return deadline == MOJO_DEADLINE_INDEFINITE ? base::TimeTicks() :
       internal::NowTicks() + base::TimeDelta::FromMicroseconds(deadline);
@@ -106,9 +100,9 @@ void WatcherBackend::StartWatching(const WatchData& data) {
   DCHECK_EQ(0u, handle_to_data_.count(data.handle));
 
   handle_to_data_[data.handle] = data;
-  message_pump_mojo->AddHandler(this, data.handle,
-                                data.handle_signals,
-                                data.deadline);
+  MessagePumpMojo::current()->AddHandler(this, data.handle,
+                                         data.handle_signals,
+                                         data.deadline);
 }
 
 void WatcherBackend::StopWatching(WatcherID watcher_id) {
@@ -117,7 +111,7 @@ void WatcherBackend::StopWatching(WatcherID watcher_id) {
   Handle handle;
   if (GetMojoHandleByWatcherID(watcher_id, &handle)) {
     handle_to_data_.erase(handle);
-    message_pump_mojo->RemoveHandler(handle);
+    MessagePumpMojo::current()->RemoveHandler(handle);
   }
 }
 
@@ -128,7 +122,7 @@ void WatcherBackend::RemoveAndNotify(const Handle& handle,
 
   const WatchData data(handle_to_data_[handle]);
   handle_to_data_.erase(handle);
-  message_pump_mojo->RemoveHandler(handle);
+  MessagePumpMojo::current()->RemoveHandler(handle);
   data.message_loop->PostTask(FROM_HERE, base::Bind(data.callback, result));
 }
 
@@ -312,58 +306,43 @@ void WatcherThreadManager::ProcessRequestsOnBackendThread() {
 WatcherThreadManager::WatcherThreadManager()
     : thread_(kWatcherThreadName) {
   base::Thread::Options thread_options;
-  thread_options.message_pump_factory = base::Bind(&CreateMessagePumpMojo);
+  thread_options.message_pump_factory = base::Bind(&MessagePumpMojo::Create);
   thread_.StartWithOptions(thread_options);
 }
 
-// HandleWatcher::State --------------------------------------------------------
+// HandleWatcher::StateBase and subclasses -------------------------------------
 
-// Represents the state of the HandleWatcher. Owns the user's callback and
+// The base class of HandleWatcher's state. Owns the user's callback and
 // monitors the current thread's MessageLoop to know when to force the callback
 // to run (with an error) even though the pipe hasn't been signaled yet.
-class HandleWatcher::State : public base::MessageLoop::DestructionObserver {
+class HandleWatcher::StateBase : public base::MessageLoop::DestructionObserver {
  public:
-  State(HandleWatcher* watcher,
-        const Handle& handle,
-        MojoHandleSignals handle_signals,
-        MojoDeadline deadline,
-        const base::Callback<void(MojoResult)>& callback)
+  StateBase(HandleWatcher* watcher,
+            const base::Callback<void(MojoResult)>& callback)
       : watcher_(watcher),
         callback_(callback),
-        got_ready_(false),
-        weak_factory_(this) {
+        got_ready_(false) {
     base::MessageLoop::current()->AddDestructionObserver(this);
-
-    watcher_id_ = WatcherThreadManager::GetInstance()->StartWatching(
-        handle,
-        handle_signals,
-        MojoDeadlineToTimeTicks(deadline),
-        base::Bind(&State::OnHandleReady, weak_factory_.GetWeakPtr()));
   }
 
-  virtual ~State() {
+  virtual ~StateBase() {
     base::MessageLoop::current()->RemoveDestructionObserver(this);
+  }
 
-    // If we've been notified the handle is ready (|got_ready_| is true) then
-    // the watch has been implicitly removed by
-    // WatcherThreadManager/MessagePumpMojo and we don't have to call
-    // StopWatching(). To do so would needlessly entail posting a task and
-    // blocking until the background thread services it.
-    if (!got_ready_)
-      WatcherThreadManager::GetInstance()->StopWatching(watcher_id_);
+ protected:
+  void NotifyHandleReady(MojoResult result) {
+    got_ready_ = true;
+    NotifyAndDestroy(result);
   }
 
+  bool got_ready() const { return got_ready_; }
+
  private:
   virtual void WillDestroyCurrentMessageLoop() OVERRIDE {
     // The current thread is exiting. Simulate a watch error.
     NotifyAndDestroy(MOJO_RESULT_ABORTED);
   }
 
-  void OnHandleReady(MojoResult result) {
-    got_ready_ = true;
-    NotifyAndDestroy(result);
-  }
-
   void NotifyAndDestroy(MojoResult result) {
     base::Callback<void(MojoResult)> callback = callback_;
     watcher_->Stop();  // Destroys |this|.
@@ -372,14 +351,96 @@ class HandleWatcher::State : public base::MessageLoop::DestructionObserver {
   }
 
   HandleWatcher* watcher_;
-  WatcherID watcher_id_;
   base::Callback<void(MojoResult)> callback_;
 
   // Have we been notified that the handle is ready?
   bool got_ready_;
 
+  DISALLOW_COPY_AND_ASSIGN(StateBase);
+};
+
+// If the thread on which HandleWatcher is used runs MessagePumpMojo,
+// SameThreadWatchingState is used to directly watch the handle on the same
+// thread.
+class HandleWatcher::SameThreadWatchingState : public StateBase,
+                                               public MessagePumpMojoHandler {
+ public:
+  SameThreadWatchingState(HandleWatcher* watcher,
+                          const Handle& handle,
+                          MojoHandleSignals handle_signals,
+                          MojoDeadline deadline,
+                          const base::Callback<void(MojoResult)>& callback)
+      : StateBase(watcher, callback),
+        handle_(handle) {
+    DCHECK(MessagePumpMojo::IsCurrent());
+
+    MessagePumpMojo::current()->AddHandler(
+        this, handle, handle_signals, MojoDeadlineToTimeTicks(deadline));
+  }
+
+  virtual ~SameThreadWatchingState() {
+    if (!got_ready())
+      MessagePumpMojo::current()->RemoveHandler(handle_);
+  }
+
+ private:
+  // MessagePumpMojoHandler overrides:
+  virtual void OnHandleReady(const Handle& handle) OVERRIDE {
+    StopWatchingAndNotifyReady(handle, MOJO_RESULT_OK);
+  }
+
+  virtual void OnHandleError(const Handle& handle, MojoResult result) OVERRIDE {
+    StopWatchingAndNotifyReady(handle, result);
+  }
+
+  void StopWatchingAndNotifyReady(const Handle& handle, MojoResult result) {
+    DCHECK_EQ(handle.value(), handle_.value());
+    MessagePumpMojo::current()->RemoveHandler(handle_);
+    NotifyHandleReady(result);
+  }
+
+  Handle handle_;
+
+  DISALLOW_COPY_AND_ASSIGN(SameThreadWatchingState);
+};
+
+// If the thread on which HandleWatcher is used runs a message pump different
+// from MessagePumpMojo, SecondaryThreadWatchingState is used to watch the
+// handle on the handle watcher thread.
+class HandleWatcher::SecondaryThreadWatchingState : public StateBase {
+ public:
+  SecondaryThreadWatchingState(HandleWatcher* watcher,
+                               const Handle& handle,
+                               MojoHandleSignals handle_signals,
+                               MojoDeadline deadline,
+                               const base::Callback<void(MojoResult)>& callback)
+      : StateBase(watcher, callback),
+        weak_factory_(this) {
+    watcher_id_ = WatcherThreadManager::GetInstance()->StartWatching(
+        handle,
+        handle_signals,
+        MojoDeadlineToTimeTicks(deadline),
+        base::Bind(&SecondaryThreadWatchingState::NotifyHandleReady,
+                   weak_factory_.GetWeakPtr()));
+  }
+
+  virtual ~SecondaryThreadWatchingState() {
+    // If we've been notified the handle is ready (|got_ready()| is true) then
+    // the watch has been implicitly removed by
+    // WatcherThreadManager/MessagePumpMojo and we don't have to call
+    // StopWatching(). To do so would needlessly entail posting a task and
+    // blocking until the background thread services it.
+    if (!got_ready())
+      WatcherThreadManager::GetInstance()->StopWatching(watcher_id_);
+  }
+
+ private:
+  WatcherID watcher_id_;
+
   // Used to weakly bind |this| to the WatcherThreadManager.
-  base::WeakPtrFactory<State> weak_factory_;
+  base::WeakPtrFactory<SecondaryThreadWatchingState> weak_factory_;
+
+  DISALLOW_COPY_AND_ASSIGN(SecondaryThreadWatchingState);
 };
 
 // HandleWatcher ---------------------------------------------------------------
@@ -397,7 +458,13 @@ void HandleWatcher::Start(const Handle& handle,
   DCHECK(handle.is_valid());
   DCHECK_NE(MOJO_HANDLE_SIGNAL_NONE, handle_signals);
 
-  state_.reset(new State(this, handle, handle_signals, deadline, callback));
+  if (MessagePumpMojo::IsCurrent()) {
+    state_.reset(new SameThreadWatchingState(
+        this, handle, handle_signals, deadline, callback));
+  } else {
+    state_.reset(new SecondaryThreadWatchingState(
+        this, handle, handle_signals, deadline, callback));
+  }
 }
 
 void HandleWatcher::Stop() {