Implements a monitor to watch for the browser hanging.

components/browser_watcher/window_hang_monitor_win.h

+// Copyright 2015 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 COMPONENTS_BROWSER_WATCHER_WINDOW_HANG_MONITOR_WIN_H_
+#define COMPONENTS_BROWSER_WATCHER_WINDOW_HANG_MONITOR_WIN_H_
+
+#include <windows.h>
+
+#include "base/callback_forward.h"
+#include "base/macros.h"
+#include "base/process/process.h"
+#include "base/strings/string16.h"
+#include "base/time/time.h"
+#include "base/timer/timer.h"
+
+namespace browser_watcher {
+
+// Monitors a window for hanging by periodically sending it a WM_NULL message
+// and timing the response.
+class WindowHangMonitor {
+ public:
+  enum WindowEvent {
+    WINDOW_HUNG,
+    WINDOW_VANISHED,
+  };
+  // Called when a hang is detected or when the window has gone away.
+  // Called precisely zero or once.

[erikwright (departed), 2015/03/25 18:57:22]

zero or one time(s).

[Sigurður Ásgeirsson, 2015/03/25 19:56:53]

Done.

+  typedef base::Callback<void(WindowEvent)> WindowEventCallback;
+
+  // Initialize the monitor with an event callback.
+  explicit WindowHangMonitor(const WindowEventCallback& callback);
+  ~WindowHangMonitor();
+
+  // Initializes the watcher to monitor the window answering to |window_name|.
+  // Returns true on success.
+  bool Initialize(const base::string16& window_name);
+
+  // Testing accessors.
+  bool IsIdleForTesting() const { return !timer_.IsRunning(); }
+  void SetPingIntervalForTesting(base::TimeDelta ping_interval);
+  void SetHangTimeoutForTesting(base::TimeDelta hang_timeout);
+
+  HWND window() const { return window_; }
+  const base::Process& window_process() const { return window_process_; }
+
+ private:
+  static void CALLBACK
+  SendAsyncProc(HWND window, UINT msg, ULONG_PTR data, LRESULT lresult);
+
+  // Checks that |window_| is still valid, and sends it a ping.

[erikwright (departed), 2015/03/25 18:57:21]

Comments for the other methods?

[Sigurður Ásgeirsson, 2015/03/25 19:56:53]

Done.

+  // Issues a |WINDOW_VANISHED| callback if the window's no longer valid.
+  // Schedules OnHangTimeout in case of success.
+  // Returns true on success, false if the window is no longer valid or other
+  // failure.
+  bool MaybeSendPing();
+  void OnPongReceived(LRESULT lresult);
+  void OnHangTimeout();
+  void OnRetryTimeout();
+
+  struct OutstandingPing {
+    WindowHangMonitor* monitor;

[erikwright (departed), 2015/03/25 18:57:21]

I believe the ordering rules would have this go above all method declaration in
the private section.

[Sigurður Ásgeirsson, 2015/03/25 19:56:53]

Done.

+  };
+
+  // Invoked on significant window events.
+  WindowEventCallback callback_;
+
+  // The registry path where a hang event will be recorded.

[erikwright (departed), 2015/03/25 18:57:21]

comment invalid

[Sigurður Ásgeirsson, 2015/03/25 19:56:53]

Done.

+  base::string16 window_name_;
+
+  // The monitored window handle.
+  HWND window_;
+
+  // The process that owned |window_| when Initialize was called.
+  base::Process window_process_;
+
+  // The time the last message was sent.
+  base::Time last_ping_;
+
+  // The ping interval, must be larger than |hang_timeout_|.
+  base::TimeDelta ping_interval_;
+  // The time after which |window_| is assumed hung.
+  base::TimeDelta hang_timeout_;
+
+  // The timer used to schedule polls.
+  base::Timer timer_;
+
+  // Non-null when there is an outstanding ping.
+  // This is intentionally leaked when a hang is detected.
+  OutstandingPing* outstanding_ping_;
+
+  DISALLOW_COPY_AND_ASSIGN(WindowHangMonitor);
+};
+
+}  // namespace browser_watcher
+
+#endif  // COMPONENTS_BROWSER_WATCHER_WINDOW_HANG_MONITOR_WIN_H_