base/threading/watchdog.cc

   1 // Copyright (c) 2012 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 #include "base/threading/watchdog.h"
   6
   7 #include "base/compiler_specific.h"
   8 #include "base/lazy_instance.h"
   9 #include "base/logging.h"
  10 #include "base/threading/platform_thread.h"
  11
  12 namespace base {
  13
  14 namespace {
  15
  16 // When the debugger breaks (when we alarm), all the other alarms that are
  17 // armed will expire (also alarm).  To diminish this effect, we track any
  18 // delay due to debugger breaks, and we *try* to adjust the effective start
  19 // time of other alarms to step past the debugging break.
  20 // Without this safety net, any alarm will typically trigger a host of follow
  21 // on alarms from callers that specify old times.
  22
  23 struct StaticData {
  24   // Lock for access of static data...
  25   Lock lock;
  26
  27   // When did we last alarm and get stuck (for a while) in a debugger?
  28   TimeTicks last_debugged_alarm_time;
  29
  30   // How long did we sit on a break in the debugger?
  31   TimeDelta last_debugged_alarm_delay;
  32 };
  33
  34 LazyInstance<StaticData>::Leaky g_static_data = LAZY_INSTANCE_INITIALIZER;
  35
  36 }  // namespace
  37
  38 // Start thread running in a Disarmed state.
  39 Watchdog::Watchdog(const TimeDelta& duration,
  40                    const std::string& thread_watched_name,
  41                    bool enabled)
  42   : enabled_(enabled),
  43     lock_(),
  44     condition_variable_(&lock_),
  45     state_(DISARMED),
  46     duration_(duration),
  47     thread_watched_name_(thread_watched_name),
  48     delegate_(this) {
  49   if (!enabled_)
  50     return;  // Don't start thread, or doing anything really.
  51   enabled_ = PlatformThread::Create(0,  // Default stack size.
  52                                     &delegate_,
  53                                     &handle_);
  54   DCHECK(enabled_);
  55 }
  56
  57 // Notify watchdog thread, and wait for it to finish up.
  58 Watchdog::~Watchdog() {
  59   if (!enabled_)
  60     return;
  61   if (!IsJoinable())
  62     Cleanup();
  63   condition_variable_.Signal();
  64   PlatformThread::Join(handle_);
  65 }
  66
  67 void Watchdog::Cleanup() {
  68   if (!enabled_)
  69     return;
  70   {
  71     AutoLock lock(lock_);
  72     state_ = SHUTDOWN;
  73   }
  74   condition_variable_.Signal();
  75 }
  76
  77 bool Watchdog::IsJoinable() {
  78   if (!enabled_)
  79     return true;
  80   AutoLock lock(lock_);
  81   return (state_ == JOINABLE);
  82 }
  83
  84 void Watchdog::Arm() {
  85   ArmAtStartTime(TimeTicks::Now());
  86 }
  87
  88 void Watchdog::ArmSomeTimeDeltaAgo(const TimeDelta& time_delta) {
  89   ArmAtStartTime(TimeTicks::Now() - time_delta);
  90 }
  91
  92 // Start clock for watchdog.
  93 void Watchdog::ArmAtStartTime(const TimeTicks start_time) {
  94   {
  95     AutoLock lock(lock_);
  96     start_time_ = start_time;
  97     state_ = ARMED;
  98   }
  99   // Force watchdog to wake up, and go to sleep with the timer ticking with the
 100   // proper duration.
 101   condition_variable_.Signal();
 102 }
 103
 104 // Disable watchdog so that it won't do anything when time expires.
 105 void Watchdog::Disarm() {
 106   AutoLock lock(lock_);
 107   state_ = DISARMED;
 108   // We don't need to signal, as the watchdog will eventually wake up, and it
 109   // will check its state and time, and act accordingly.
 110 }
 111
 112 void Watchdog::Alarm() {
 113   DVLOG(1) << "Watchdog alarmed for " << thread_watched_name_;
 114 }
 115
 116 //------------------------------------------------------------------------------
 117 // Internal private methods that the watchdog thread uses.
 118
 119 void Watchdog::ThreadDelegate::ThreadMain() {
 120   SetThreadName();
 121   TimeDelta remaining_duration;
 122   StaticData* static_data = g_static_data.Pointer();
 123   while (1) {
 124     AutoLock lock(watchdog_->lock_);
 125     while (DISARMED == watchdog_->state_)
 126       watchdog_->condition_variable_.Wait();
 127     if (SHUTDOWN == watchdog_->state_) {
 128       watchdog_->state_ = JOINABLE;
 129       return;
 130     }
 131     DCHECK(ARMED == watchdog_->state_);
 132     remaining_duration = watchdog_->duration_ -
 133         (TimeTicks::Now() - watchdog_->start_time_);
 134     if (remaining_duration.InMilliseconds() > 0) {
 135       // Spurios wake?  Timer drifts?  Go back to sleep for remaining time.
 136       watchdog_->condition_variable_.TimedWait(remaining_duration);
 137       continue;
 138     }
 139     // We overslept, so this seems like a real alarm.
 140     // Watch out for a user that stopped the debugger on a different alarm!
 141     {
 142       AutoLock static_lock(static_data->lock);
 143       if (static_data->last_debugged_alarm_time > watchdog_->start_time_) {
 144         // False alarm: we started our clock before the debugger break (last
 145         // alarm time).
 146         watchdog_->start_time_ += static_data->last_debugged_alarm_delay;
 147         if (static_data->last_debugged_alarm_time > watchdog_->start_time_)
 148           // Too many alarms must have taken place.
 149           watchdog_->state_ = DISARMED;
 150         continue;
 151       }
 152     }
 153     watchdog_->state_ = DISARMED;  // Only alarm at most once.
 154     TimeTicks last_alarm_time = TimeTicks::Now();
 155     {
 156       AutoUnlock unlock(watchdog_->lock_);
 157       watchdog_->Alarm();  // Set a break point here to debug on alarms.
 158     }
 159     TimeDelta last_alarm_delay = TimeTicks::Now() - last_alarm_time;
 160     if (last_alarm_delay <= TimeDelta::FromMilliseconds(2))
 161       continue;
 162     // Ignore race of two alarms/breaks going off at roughly the same time.
 163     AutoLock static_lock(static_data->lock);
 164     // This was a real debugger break.
 165     static_data->last_debugged_alarm_time = last_alarm_time;
 166     static_data->last_debugged_alarm_delay = last_alarm_delay;
 167   }
 168 }
 169
 170 void Watchdog::ThreadDelegate::SetThreadName() const {
 171   std::string name = watchdog_->thread_watched_name_ + " Watchdog";
 172   PlatformThread::SetName(name.c_str());
 173   DVLOG(1) << "Watchdog active: " << name;
 174 }
 175
 176 // static
 177 void Watchdog::ResetStaticData() {
 178   StaticData* static_data = g_static_data.Pointer();
 179   AutoLock lock(static_data->lock);
 180   static_data->last_debugged_alarm_time = TimeTicks();
 181   static_data->last_debugged_alarm_delay = TimeDelta();
 182 }
 183
 184 }  // namespace base