base/watchdog.h

   1 // Copyright (c) 2006-2008 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_WATCHDOG_H__
  19 #define BASE_WATCHDOG_H__
  20 #pragma once
  21
  22 #include <string>
  23
  24 #include "base/condition_variable.h"
  25 #include "base/lock.h"
  26 #include "base/logging.h"
  27 #include "base/platform_thread.h"
  28 #include "base/time.h"
  29
  30 class Watchdog {
  31  public:
  32   // Constructor specifies how long the Watchdog will wait before alarming.
  33   Watchdog(const base::TimeDelta& duration,
  34            const std::string& thread_watched_name,
  35            bool enabled);
  36   virtual ~Watchdog();
  37
  38   // Start timing, and alarm when time expires (unless we're disarm()ed.)
  39   void Arm();  // Arm  starting now.
  40   void ArmSomeTimeDeltaAgo(const base::TimeDelta& time_delta);
  41   void ArmAtStartTime(const base::TimeTicks start_time);
  42
  43   // Reset time, and do not set off the alarm.
  44   void Disarm();
  45
  46   // Alarm is called if the time expires after an Arm() without someone calling
  47   // Disarm().  This method can be overridden to create testable classes.
  48   virtual void Alarm() {
  49     DLOG(INFO) << "Watchdog alarmed for " << thread_watched_name_;
  50   }
  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     Watchdog* watchdog_;
  64
  65     void SetThreadName() const;
  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 base::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   base::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 base::TimeTicks last_debugged_alarm_time_;
  91   // How long did we sit on a break in the debugger?
  92   static base::TimeDelta last_debugged_alarm_delay_;
  93
  94   DISALLOW_COPY_AND_ASSIGN(Watchdog);
  95 };
  96
  97 #endif  // BASE_WATCHDOG_H__