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// Copyright (c) 2006-2008 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.
// The Watchdog class creates a second thread that can Alarm if a specific
// duration of time passes without proper attention. The duration of time is
// specified at construction time. The Watchdog may be used many times by
// simply calling Arm() (to start timing) and Disarm() (to reset the timer).
// The Watchdog is typically used under a debugger, where the stack traces on
// other threads can be examined if/when the Watchdog alarms.
// Some watchdogs will be enabled or disabled via command line switches. To
// facilitate such code, an "enabled" argument for the constuctor can be used
// to permanently disable the watchdog. Disabled watchdogs don't even spawn
// a second thread, and their methods call (Arm() and Disarm()) return very
// quickly.
#include <string>
#include "base/condition_variable.h"
#include "base/lock.h"
#include "base/logging.h"
#include "base/platform_thread.h"
#include "base/time.h"
class Watchdog {
// Constructor specifies how long the Watchdog will wait before alarming.
Watchdog(const base::TimeDelta& duration,
const std::string& thread_watched_name,
bool enabled);
virtual ~Watchdog();
// Start timing, and alarm when time expires (unless we're disarm()ed.)
void Arm(); // Arm starting now.
void ArmSomeTimeDeltaAgo(const base::TimeDelta& time_delta);
void ArmAtStartTime(const base::TimeTicks start_time);
// Reset time, and do not set off the alarm.
void Disarm();
// Alarm is called if the time expires after an Arm() without someone calling
// Disarm(). This method can be overridden to create testable classes.
virtual void Alarm() {
DLOG(INFO) << "Watchdog alarmed for " << thread_watched_name_;
// Reset static data to initial state. Useful for tests, to ensure
// they are independent.
static void ResetStaticData();
class ThreadDelegate : public PlatformThread::Delegate {
explicit ThreadDelegate(Watchdog* watchdog) : watchdog_(watchdog) {
virtual void ThreadMain();
Watchdog* watchdog_;
void SetThreadName() const;
bool init_successful_;
Lock lock_; // Mutex for state_.
ConditionVariable condition_variable_;
State state_;
const base::TimeDelta duration_; // How long after start_time_ do we alarm?
const std::string thread_watched_name_;
PlatformThreadHandle handle_;
ThreadDelegate delegate_; // Store it, because it must outlive the thread.
base::TimeTicks start_time_; // Start of epoch, and alarm after duration_.
// When the debugger breaks (when we alarm), all the other alarms that are
// armed will expire (also alarm). To diminish this effect, we track any
// delay due to debugger breaks, and we *try* to adjust the effective start
// time of other alarms to step past the debugging break.
// Without this safety net, any alarm will typically trigger a host of follow
// on alarms from callers that specify old times.
static Lock static_lock_; // Lock for access of static data...
// When did we last alarm and get stuck (for a while) in a debugger?
static base::TimeTicks last_debugged_alarm_time_;
// How long did we sit on a break in the debugger?
static base::TimeDelta last_debugged_alarm_delay_;
#endif // BASE_WATCHDOG_H__
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