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 30 namespace base { 31 32 class 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
