Revert of Mojo C++ bindings: support sync methods - part 2

mojo/public/cpp/bindings/lib/sync_handle_watcher.h

-// 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.
-
-#ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_SYNC_HANDLE_WATCHER_H_
-#define MOJO_PUBLIC_CPP_BINDINGS_LIB_SYNC_HANDLE_WATCHER_H_
-
-#include <unordered_map>
-
-#include "base/callback.h"
-#include "base/macros.h"
-#include "base/message_loop/message_loop.h"
-#include "base/threading/thread_checker.h"
-#include "mojo/public/cpp/system/core.h"
-
-namespace mojo {
-namespace internal {
-
-// SyncHandleWatcher is used to support sync methods. While a sync call is
-// waiting for response, we would like incoming sync method requests on the same
-// thread to be able to reenter. We also would like master endpoints to continue
-// dispatching messages for associated endpoints on different threads.
-// Therefore, SyncHandleWatcher is used as thread-local storage to register all
-// handles that need to be watched while waiting for sync call responses.
-//
-// This class is not thread safe.
-class SyncHandleWatcher : public base::MessageLoop::DestructionObserver {
- public:
-  // Returns a thread-local object.
-  static SyncHandleWatcher* current();
-
-  using HandleCallback = base::Callback<void(MojoResult)>;
-  bool RegisterHandle(const Handle& handle,
-                      MojoHandleSignals handle_signals,
-                      const HandleCallback& callback);
-
-  void UnregisterHandle(const Handle& handle);
-
-  // Waits on all the registered handles and runs callbacks synchronously for
-  // those ready handles.
-  // The method:
-  //   - returns true when |*should_stop| is set to true;
-  //   - returns false when either |caller_handle| is unregistered or any error
-  //     occurs.
-  bool WatchAllHandles(const Handle& caller_handle, const bool* should_stop);
-
- private:
-  struct HandleHasher {
-    size_t operator()(const Handle& handle) const {
-      return std::hash<uint32_t>()(static_cast<uint32_t>(handle.value()));
-    }
-  };
-  using HandleMap = std::unordered_map<Handle, HandleCallback, HandleHasher>;
-
-  SyncHandleWatcher();
-  ~SyncHandleWatcher() override;
-
-  // base::MessageLoop::DestructionObserver implementation:
-  void WillDestroyCurrentMessageLoop() override;
-
-  HandleMap handles_;
-
-  ScopedHandle wait_set_handle_;
-
-  base::ThreadChecker thread_checker_;
-
-  DISALLOW_COPY_AND_ASSIGN(SyncHandleWatcher);
-};
-
-}  // namespace internal
-}  // namespace mojo
-
-#endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_SYNC_HANDLE_WATCHER_H_