Use Mojo pipes to signal sync IPC events

ipc/ipc_sync_message_filter.cc

Index: ipc/ipc_sync_message_filter.cc
diff --git a/ipc/ipc_sync_message_filter.cc b/ipc/ipc_sync_message_filter.cc
index e917655cd85912b15210818516433c04cbeefa98..5fe03a269d948f0986156b0366f59f42462660ca 100644
--- a/ipc/ipc_sync_message_filter.cc
+++ b/ipc/ipc_sync_message_filter.cc
@@ -7,20 +7,36 @@
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/logging.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
+
 bool SyncMessageFilter::Send(Message* message) {
   if (!message->is_sync()) {
     {
       base::AutoLock auto_lock(lock_);
       if (!io_task_runner_.get()) {
-        pending_messages_.push_back(message);
+        pending_messages_.emplace_back(base::WrapUnique(message));
         return true;
       }
     }
@@ -30,9 +46,7 @@ bool SyncMessageFilter::Send(Message* message) {
     return true;
   }
 
-  base::WaitableEvent done_event(
-      base::WaitableEvent::ResetPolicy::MANUAL,
-      base::WaitableEvent::InitialState::NOT_SIGNALED);
+  MojoEvent done_event;
   PendingSyncMsg pending_message(
       SyncMessage::GetMessageId(*message),
       static_cast<SyncMessage*>(message)->GetReplyDeserializer(),
@@ -53,15 +67,33 @@ bool SyncMessageFilter::Send(Message* message) {
           FROM_HERE,
           base::Bind(&SyncMessageFilter::SendOnIOThread, this, message));
     } else {
-      pending_messages_.push_back(message);
+      pending_messages_.emplace_back(base::WrapUnique(message));
     }
   }
 
-  base::WaitableEvent* events[2] = { shutdown_event_, &done_event };
-  if (base::WaitableEvent::WaitMany(events, 2) == 1) {
+  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 };
+  bool result = registry->WatchAllHandles(stop_flags, 2);
+  DCHECK(result);
+  DCHECK(!error);
+
+  if (done) {
     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_);
@@ -73,26 +105,31 @@ bool SyncMessageFilter::Send(Message* message) {
 }
 
 void SyncMessageFilter::OnFilterAdded(Sender* sender) {
-  std::vector<Message*> pending_messages;
+  std::vector<std::unique_ptr<Message>> pending_messages;
   {
     base::AutoLock auto_lock(lock_);
     sender_ = sender;
     io_task_runner_ = base::ThreadTaskRunnerHandle::Get();
-    pending_messages_.release(&pending_messages);
+    shutdown_watcher_.StartWatching(
+        shutdown_event_,
+        base::Bind(&SyncMessageFilter::OnShutdownEventSignaled, this));
+    std::swap(pending_messages_, pending_messages);
   }
-  for (auto* msg : pending_messages)
-    SendOnIOThread(msg);
+  for (auto& msg : pending_messages)
+    SendOnIOThread(msg.release());
 }
 
 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();
 }
 
@@ -167,4 +204,9 @@ void SyncMessageFilter::SignalAllEvents() {
   }
 }
 
+void SyncMessageFilter::OnShutdownEventSignaled(base::WaitableEvent* event) {
+  DCHECK_EQ(event, shutdown_event_);
+  shutdown_mojo_event_.Signal();
+}
+
 }  // namespace IPC