Revert Mojo-based SyncChannel waiting again

ipc/ipc_sync_message_filter.cc

 // Copyright (c) 2012 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 "ipc/ipc_sync_message_filter.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.h"
-#include "base/macros.h"
-#include "base/memory/ptr_util.h"
-#include "base/memory/ref_counted.h"
-#include "base/message_loop/message_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "ipc/ipc_channel.h"
 #include "ipc/ipc_sync_message.h"
-#include "ipc/mojo_event.h"
-#include "mojo/public/cpp/bindings/sync_handle_registry.h"
 
 namespace IPC {
 
-namespace {
-
-// A generic callback used when watching handles synchronously. Sets |*signal|
-// to true. Also sets |*error| to true in case of an error.
-void OnSyncHandleReady(bool* signal, bool* error, MojoResult result) {
-  *signal = true;
-  *error = result != MOJO_RESULT_OK;
-}
-
-}  // namespace
-
-// A helper class created by SyncMessageFilter to watch the lifetime of the IO
-// MessageLoop. This holds a weak ref to the SyncMessageFilter and notifies it
-// on its own thread if the SyncMessageFilter is still alive at the time of
-// IO MessageLoop destruction.
-class SyncMessageFilter::IOMessageLoopObserver
-    : public base::MessageLoop::DestructionObserver,
-      public base::RefCountedThreadSafe<IOMessageLoopObserver> {
- public:
-  IOMessageLoopObserver(
-      base::WeakPtr<SyncMessageFilter> weak_filter,
-      scoped_refptr<base::SingleThreadTaskRunner> filter_task_runner)
-      : weak_filter_(weak_filter), filter_task_runner_(filter_task_runner) {}
-
-  void StartOnIOThread() {
-    DCHECK(!watching_);
-    watching_ = true;
-    io_task_runner_ = base::ThreadTaskRunnerHandle::Get();
-    base::MessageLoop::current()->AddDestructionObserver(this);
-  }
-
-  void Stop() {
-    if (!io_task_runner_)
-      return;
-
-    if (io_task_runner_->BelongsToCurrentThread()) {
-      StopOnIOThread();
-    } else {
-      io_task_runner_->PostTask(
-          FROM_HERE, base::Bind(&IOMessageLoopObserver::StopOnIOThread, this));
-    }
-  }
-
- private:
-  void StopOnIOThread() {
-    DCHECK(io_task_runner_->BelongsToCurrentThread());
-    if (!watching_)
-      return;
-    watching_ = false;
-    base::MessageLoop::current()->RemoveDestructionObserver(this);
-  }
-
-  // base::MessageLoop::DestructionObserver:
-  void WillDestroyCurrentMessageLoop() override {
-    DCHECK(io_task_runner_ && io_task_runner_->BelongsToCurrentThread());
-    DCHECK(watching_);
-    StopOnIOThread();
-    filter_task_runner_->PostTask(
-        FROM_HERE,
-        base::Bind(&SyncMessageFilter::OnIOMessageLoopDestroyed, weak_filter_));
-  }
-
-  friend class base::RefCountedThreadSafe<IOMessageLoopObserver>;
-
-  ~IOMessageLoopObserver() override {}
-
-  bool watching_ = false;
-  base::WeakPtr<SyncMessageFilter> weak_filter_;
-  scoped_refptr<base::SingleThreadTaskRunner> filter_task_runner_;
-  scoped_refptr<base::SingleThreadTaskRunner> io_task_runner_;
-
-  DISALLOW_COPY_AND_ASSIGN(IOMessageLoopObserver);
-};
-
 bool SyncMessageFilter::Send(Message* message) {
   if (!message->is_sync()) {
     {
       base::AutoLock auto_lock(lock_);
       if (sender_ && is_channel_send_thread_safe_) {
         sender_->Send(message);
         return true;
       } else if (!io_task_runner_.get()) {
-        pending_messages_.emplace_back(base::WrapUnique(message));
+        pending_messages_.push_back(message);
         return true;
       }
     }
     io_task_runner_->PostTask(
         FROM_HERE,
         base::Bind(&SyncMessageFilter::SendOnIOThread, this, message));
     return true;
   }
 
-  MojoEvent done_event;
+  base::WaitableEvent done_event(
+      base::WaitableEvent::ResetPolicy::MANUAL,
+      base::WaitableEvent::InitialState::NOT_SIGNALED);
   PendingSyncMsg pending_message(
       SyncMessage::GetMessageId(*message),
       static_cast<SyncMessage*>(message)->GetReplyDeserializer(),
       &done_event);
 
   {
     base::AutoLock auto_lock(lock_);
     // Can't use this class on the main thread or else it can lead to deadlocks.
     // Also by definition, can't use this on IO thread since we're blocking it.
     if (base::ThreadTaskRunnerHandle::IsSet()) {
       DCHECK(base::ThreadTaskRunnerHandle::Get() != listener_task_runner_);
       DCHECK(base::ThreadTaskRunnerHandle::Get() != io_task_runner_);
     }
     pending_sync_messages_.insert(&pending_message);
 
     if (io_task_runner_.get()) {
       io_task_runner_->PostTask(
           FROM_HERE,
           base::Bind(&SyncMessageFilter::SendOnIOThread, this, message));
     } else {
-      pending_messages_.emplace_back(base::WrapUnique(message));
+      pending_messages_.push_back(message);
     }
   }
 
-  bool done = false;
-  bool shutdown = false;
-  bool error = false;
-  scoped_refptr<mojo::SyncHandleRegistry> registry =
-      mojo::SyncHandleRegistry::current();
-  registry->RegisterHandle(shutdown_mojo_event_.GetHandle(),
-                           MOJO_HANDLE_SIGNAL_READABLE,
-                           base::Bind(&OnSyncHandleReady, &shutdown, &error));
-  registry->RegisterHandle(done_event.GetHandle(),
-                           MOJO_HANDLE_SIGNAL_READABLE,
-                           base::Bind(&OnSyncHandleReady, &done, &error));
-
-  const bool* stop_flags[] = { &done, &shutdown };
-  registry->WatchAllHandles(stop_flags, 2);
-  DCHECK(!error);
-
-  if (done) {
+  base::WaitableEvent* events[2] = { shutdown_event_, &done_event };
+  if (base::WaitableEvent::WaitMany(events, 2) == 1) {
     TRACE_EVENT_FLOW_END0(TRACE_DISABLED_BY_DEFAULT("ipc.flow"),
                           "SyncMessageFilter::Send", &done_event);
   }
-  registry->UnregisterHandle(shutdown_mojo_event_.GetHandle());
-  registry->UnregisterHandle(done_event.GetHandle());
 
   {
     base::AutoLock auto_lock(lock_);
     delete pending_message.deserializer;
     pending_sync_messages_.erase(&pending_message);
   }
 
   return pending_message.send_result;
 }
 
 void SyncMessageFilter::OnFilterAdded(Sender* sender) {
-  std::vector<std::unique_ptr<Message>> pending_messages;
+  std::vector<Message*> pending_messages;
   {
     base::AutoLock auto_lock(lock_);
     sender_ = sender;
     io_task_runner_ = base::ThreadTaskRunnerHandle::Get();
-    shutdown_watcher_.StartWatching(
-        shutdown_event_,
-        base::Bind(&SyncMessageFilter::OnShutdownEventSignaled, this));
-    io_message_loop_observer_->StartOnIOThread();
-    std::swap(pending_messages_, pending_messages);
+    pending_messages_.release(&pending_messages);
   }
-  for (auto& msg : pending_messages)
-    SendOnIOThread(msg.release());
+  for (auto* msg : pending_messages)
+    SendOnIOThread(msg);
 }
 
 void SyncMessageFilter::OnChannelError() {
   base::AutoLock auto_lock(lock_);
   sender_ = NULL;
-  shutdown_watcher_.StopWatching();
   SignalAllEvents();
 }
 
 void SyncMessageFilter::OnChannelClosing() {
   base::AutoLock auto_lock(lock_);
   sender_ = NULL;
-  shutdown_watcher_.StopWatching();
   SignalAllEvents();
 }
 
 bool SyncMessageFilter::OnMessageReceived(const Message& message) {
   base::AutoLock auto_lock(lock_);
   for (PendingSyncMessages::iterator iter = pending_sync_messages_.begin();
        iter != pending_sync_messages_.end(); ++iter) {
     if (SyncMessage::IsMessageReplyTo(message, (*iter)->id)) {
       if (!message.is_reply_error()) {
         (*iter)->send_result =
             (*iter)->deserializer->SerializeOutputParameters(message);
       }
       TRACE_EVENT_FLOW_BEGIN0(TRACE_DISABLED_BY_DEFAULT("ipc.flow"),
                               "SyncMessageFilter::OnMessageReceived",
                               (*iter)->done_event);
       (*iter)->done_event->Signal();
       return true;
     }
   }
 
   return false;
 }
 
 SyncMessageFilter::SyncMessageFilter(base::WaitableEvent* shutdown_event,
                                      bool is_channel_send_thread_safe)
     : sender_(NULL),
       is_channel_send_thread_safe_(is_channel_send_thread_safe),
       listener_task_runner_(base::ThreadTaskRunnerHandle::Get()),
-      shutdown_event_(shutdown_event),
-      weak_factory_(this) {
-  io_message_loop_observer_ = new IOMessageLoopObserver(
-      weak_factory_.GetWeakPtr(), listener_task_runner_);
+      shutdown_event_(shutdown_event) {
 }
 
 SyncMessageFilter::~SyncMessageFilter() {
-  io_message_loop_observer_->Stop();
 }
 
 void SyncMessageFilter::SendOnIOThread(Message* message) {
   if (sender_) {
     sender_->Send(message);
     return;
   }
 
   if (message->is_sync()) {
     // We don't know which thread sent it, but it doesn't matter, just signal
     // them all.
     base::AutoLock auto_lock(lock_);
     SignalAllEvents();
   }
 
   delete message;
 }
 
 void SyncMessageFilter::SignalAllEvents() {
   lock_.AssertAcquired();
   for (PendingSyncMessages::iterator iter = pending_sync_messages_.begin();
        iter != pending_sync_messages_.end(); ++iter) {
     TRACE_EVENT_FLOW_BEGIN0(TRACE_DISABLED_BY_DEFAULT("ipc.flow"),
                             "SyncMessageFilter::SignalAllEvents",
                             (*iter)->done_event);
     (*iter)->done_event->Signal();
   }
 }
 
-void SyncMessageFilter::OnShutdownEventSignaled(base::WaitableEvent* event) {
-  DCHECK_EQ(event, shutdown_event_);
-  shutdown_mojo_event_.Signal();
-}
-
-void SyncMessageFilter::OnIOMessageLoopDestroyed() {
-  // Since we use an async WaitableEventWatcher to watch the shutdown event
-  // from the IO thread, we can't forward the shutdown signal after the IO
-  // message loop is destroyed. Since that destruction indicates shutdown
-  // anyway, we manually signal the shutdown event in this case.
-  shutdown_mojo_event_.Signal();
-}
-
 }  // namespace IPC