Use Mojo pipes to signal sync IPC events

mojo/public/cpp/bindings/lib/sync_handle_registry.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_REGISTRY_H_
-#define MOJO_PUBLIC_CPP_BINDINGS_LIB_SYNC_HANDLE_REGISTRY_H_
-
-#include <unordered_map>
-
-#include "base/callback.h"
-#include "base/macros.h"
-#include "base/memory/ref_counted.h"
-#include "base/threading/thread_checker.h"
-#include "mojo/public/cpp/system/core.h"
-
-namespace mojo {
-namespace internal {
-
-// SyncHandleRegistry is a thread-local storage to register handles that want to
-// be watched together.
-//
-// This class is not thread safe.
-class SyncHandleRegistry : public base::RefCounted<SyncHandleRegistry> {
- public:
-  // Returns a thread-local object.
-  static scoped_refptr<SyncHandleRegistry> 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 any element of |should_stop| is set to true;
-  //   - returns false when any error occurs.
-  bool WatchAllHandles(const bool* should_stop[], size_t count);
-
- private:
-  friend class base::RefCounted<SyncHandleRegistry>;
-
-  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>;
-
-  SyncHandleRegistry();
-  ~SyncHandleRegistry();
-
-  HandleMap handles_;
-
-  ScopedHandle wait_set_handle_;
-
-  base::ThreadChecker thread_checker_;
-
-  DISALLOW_COPY_AND_ASSIGN(SyncHandleRegistry);
-};
-
-}  // namespace internal
-}  // namespace mojo
-
-#endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_SYNC_HANDLE_REGISTRY_H_