Use Mojo pipes to signal sync IPC events

ipc/mojo_event.cc

+// Copyright 2016 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/mojo_event.h"
+
+namespace IPC {
+
+MojoEvent::MojoEvent() {
+  mojo::MessagePipe pipe;
+  signal_handle_ = std::move(pipe.handle0);
+  wait_handle_ = std::move(pipe.handle1);
+}
+
+MojoEvent::~MojoEvent() {}
+
+void MojoEvent::Signal() {
+  base::AutoLock lock(lock_);
+  if (is_signaled_)
+    return;
+  is_signaled_ = true;
+  MojoResult rv = mojo::WriteMessageRaw(
+      signal_handle_.get(), nullptr, 0, nullptr, 0,
+      MOJO_WRITE_MESSAGE_FLAG_NONE);
+  DCHECK_EQ(rv, MOJO_RESULT_OK);
+}
+
+void MojoEvent::Reset() {
+  base::AutoLock lock(lock_);
+  if (!is_signaled_)
+    return;
+  is_signaled_ = false;
+  MojoResult rv = mojo::ReadMessageRaw(
+      wait_handle_.get(), nullptr, nullptr, nullptr, nullptr,
+      MOJO_READ_MESSAGE_FLAG_NONE);
+  DCHECK_EQ(rv, MOJO_RESULT_OK);
+}
+
+}  // namespace IPC