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// Copyright 2017 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 "base/callback.h"
#include "base/macros.h"
#include "mojo/public/c/system/types.h"
#include "mojo/public/cpp/system/handle.h"
#include "mojo/public/cpp/system/simple_watcher.h"
#include "mojo/public/cpp/system/system_export.h"
namespace mojo {
// This class helps track the state of specific signal on a handle so that
// the user doesn't have to manually query the signal state every time they
// want to know the handle's state.
// Usage of this class is specifically targeting cases where the signal state
// changes infrequently but must be queried frequently. If either condition does
// not hold, consider using Handle::QuerySignalsState (or
// MojoQueryHandleSignalsState) directly instead.
class MOJO_CPP_SYSTEM_EXPORT HandleSignalTracker {
using NotificationCallback =
base::Callback<void(const HandleSignalsState& signals_state)>;
// Constructs a tracker which tracks |signals| on |handle|. |signals| may
// be any single signal flag or any combination of signal flags.
HandleSignalTracker(Handle handle, MojoHandleSignals signals);
const HandleSignalsState& last_known_state() const {
return last_known_state_;
// Sets an optional callback to be invoked any time the tracker is notified of
// a relevant state change.
void set_notification_callback(const NotificationCallback& callback) {
notification_callback_ = callback;
class State;
void Arm();
void OnNotify(MojoResult result, const HandleSignalsState& state);
NotificationCallback notification_callback_;
// The last known signaliing state of the handle.
HandleSignalsState last_known_state_ = {0, 0};
// Watches for the signal(s) to be signaled. May only be armed when
// |low_watcher_| is not.
SimpleWatcher high_watcher_;
// Watches for the signal(s) to be cleared. May only be armed when
// |high_watcher_| is not.
SimpleWatcher low_watcher_;
} // namespace mojo