1// Copyright (c) 2011 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5// The Watchdog class creates a second thread that can Alarm if a specific
6// duration of time passes without proper attention.  The duration of time is
7// specified at construction time.  The Watchdog may be used many times by
8// simply calling Arm() (to start timing) and Disarm() (to reset the timer).
9// The Watchdog is typically used under a debugger, where the stack traces on
10// other threads can be examined if/when the Watchdog alarms.
11
12// Some watchdogs will be enabled or disabled via command line switches. To
13// facilitate such code, an "enabled" argument for the constuctor can be used
14// to permanently disable the watchdog.  Disabled watchdogs don't even spawn
15// a second thread, and their methods call (Arm() and Disarm()) return very
16// quickly.
17
18#ifndef BASE_THREADING_WATCHDOG_H_
19#define BASE_THREADING_WATCHDOG_H_
20#pragma once
21
22#include <string>
23
24#include "base/base_api.h"
25#include "base/synchronization/condition_variable.h"
26#include "base/synchronization/lock.h"
27#include "base/threading/platform_thread.h"
28#include "base/time.h"
29
30namespace base {
31
32class BASE_API Watchdog {
33 public:
34  // Constructor specifies how long the Watchdog will wait before alarming.
35  Watchdog(const TimeDelta& duration,
36           const std::string& thread_watched_name,
37           bool enabled);
38  virtual ~Watchdog();
39
40  // Start timing, and alarm when time expires (unless we're disarm()ed.)
41  void Arm();  // Arm  starting now.
42  void ArmSomeTimeDeltaAgo(const TimeDelta& time_delta);
43  void ArmAtStartTime(const TimeTicks start_time);
44
45  // Reset time, and do not set off the alarm.
46  void Disarm();
47
48  // Alarm is called if the time expires after an Arm() without someone calling
49  // Disarm().  This method can be overridden to create testable classes.
50  virtual void Alarm();
51
52  // Reset static data to initial state. Useful for tests, to ensure
53  // they are independent.
54  static void ResetStaticData();
55
56 private:
57  class ThreadDelegate : public PlatformThread::Delegate {
58   public:
59    explicit ThreadDelegate(Watchdog* watchdog) : watchdog_(watchdog) {
60    }
61    virtual void ThreadMain();
62   private:
63    void SetThreadName() const;
64
65    Watchdog* watchdog_;
66  };
67
68  enum State {ARMED, DISARMED, SHUTDOWN };
69
70  bool init_successful_;
71
72  Lock lock_;  // Mutex for state_.
73  ConditionVariable condition_variable_;
74  State state_;
75  const TimeDelta duration_;  // How long after start_time_ do we alarm?
76  const std::string thread_watched_name_;
77  PlatformThreadHandle handle_;
78  ThreadDelegate delegate_;  // Store it, because it must outlive the thread.
79
80  TimeTicks start_time_;  // Start of epoch, and alarm after duration_.
81
82  // When the debugger breaks (when we alarm), all the other alarms that are
83  // armed will expire (also alarm).  To diminish this effect, we track any
84  // delay due to debugger breaks, and we *try* to adjust the effective start
85  // time of other alarms to step past the debugging break.
86  // Without this safety net, any alarm will typically trigger a host of follow
87  // on alarms from callers that specify old times.
88  static Lock static_lock_;  // Lock for access of static data...
89  // When did we last alarm and get stuck (for a while) in a debugger?
90  static TimeTicks last_debugged_alarm_time_;
91  // How long did we sit on a break in the debugger?
92  static TimeDelta last_debugged_alarm_delay_;
93
94  DISALLOW_COPY_AND_ASSIGN(Watchdog);
95};
96
97}  // namespace base
98
99#endif  // BASE_THREADING_WATCHDOG_H_
100