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// Copyright (c) 2012 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/base_export.h"
#include "base/compiler_specific.h"
#include "base/synchronization/condition_variable.h"
#include "base/synchronization/lock.h"
#include "base/threading/platform_thread.h"
#include "base/time.h"
namespace base {
class BASE_EXPORT Watchdog {
// Constructor specifies how long the Watchdog will wait before alarming.
Watchdog(const TimeDelta& duration,
const std::string& thread_watched_name,
bool enabled);
virtual ~Watchdog();
// Notify watchdog thread to finish up. Sets the state_ to SHUTDOWN.
void Cleanup();
// Returns true if we state_ is JOINABLE (which indicates that Watchdog has
// exited).
bool IsJoinable();
// Start timing, and alarm when time expires (unless we're disarm()ed.)
void Arm(); // Arm starting now.
void ArmSomeTimeDeltaAgo(const TimeDelta& time_delta);
void ArmAtStartTime(const 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();
// 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() override;
void SetThreadName() const;
Watchdog* watchdog_;
bool enabled_;
Lock lock_; // Mutex for state_.
ConditionVariable condition_variable_;
State state_;
const 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.
TimeTicks start_time_; // Start of epoch, and alarm after duration_.
} // namespace base