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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.
#include "base/threading/watchdog.h"
#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/no_destructor.h"
#include "base/threading/platform_thread.h"
namespace base {
namespace {
// 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.
struct StaticData {
// Lock for access of static data...
Lock lock;
// When did we last alarm and get stuck (for a while) in a debugger?
TimeTicks last_debugged_alarm_time;
// How long did we sit on a break in the debugger?
TimeDelta last_debugged_alarm_delay;
};
StaticData* GetStaticData() {
static base::NoDestructor<StaticData> static_data;
return static_data.get();
}
} // namespace
// Start thread running in a Disarmed state.
Watchdog::Watchdog(const TimeDelta& duration,
const std::string& thread_watched_name,
bool enabled)
: enabled_(enabled),
lock_(),
condition_variable_(&lock_),
state_(DISARMED),
duration_(duration),
thread_watched_name_(thread_watched_name),
delegate_(this) {
if (!enabled_)
return; // Don't start thread, or doing anything really.
enabled_ = PlatformThread::Create(0, // Default stack size.
&delegate_,
&handle_);
DCHECK(enabled_);
}
// Notify watchdog thread, and wait for it to finish up.
Watchdog::~Watchdog() {
if (!enabled_)
return;
if (!IsJoinable())
Cleanup();
PlatformThread::Join(handle_);
}
void Watchdog::Cleanup() {
if (!enabled_)
return;
AutoLock lock(lock_);
state_ = SHUTDOWN;
condition_variable_.Signal();
}
bool Watchdog::IsJoinable() {
if (!enabled_)
return true;
AutoLock lock(lock_);
return (state_ == JOINABLE);
}
void Watchdog::Arm() {
ArmAtStartTime(TimeTicks::Now());
}
void Watchdog::ArmSomeTimeDeltaAgo(const TimeDelta& time_delta) {
ArmAtStartTime(TimeTicks::Now() - time_delta);
}
// Start clock for watchdog.
void Watchdog::ArmAtStartTime(const TimeTicks start_time) {
AutoLock lock(lock_);
start_time_ = start_time;
state_ = ARMED;
// Force watchdog to wake up, and go to sleep with the timer ticking with the
// proper duration.
condition_variable_.Signal();
}
// Disable watchdog so that it won't do anything when time expires.
void Watchdog::Disarm() {
AutoLock lock(lock_);
state_ = DISARMED;
// We don't need to signal, as the watchdog will eventually wake up, and it
// will check its state and time, and act accordingly.
}
void Watchdog::Alarm() {
DVLOG(1) << "Watchdog alarmed for " << thread_watched_name_;
}
//------------------------------------------------------------------------------
// Internal private methods that the watchdog thread uses.
void Watchdog::ThreadDelegate::ThreadMain() {
SetThreadName();
TimeDelta remaining_duration;
StaticData* static_data = GetStaticData();
while (1) {
AutoLock lock(watchdog_->lock_);
while (DISARMED == watchdog_->state_)
watchdog_->condition_variable_.Wait();
if (SHUTDOWN == watchdog_->state_) {
watchdog_->state_ = JOINABLE;
return;
}
DCHECK(ARMED == watchdog_->state_);
remaining_duration = watchdog_->duration_ -
(TimeTicks::Now() - watchdog_->start_time_);
if (remaining_duration.InMilliseconds() > 0) {
// Spurios wake? Timer drifts? Go back to sleep for remaining time.
watchdog_->condition_variable_.TimedWait(remaining_duration);
continue;
}
// We overslept, so this seems like a real alarm.
// Watch out for a user that stopped the debugger on a different alarm!
{
AutoLock static_lock(static_data->lock);
if (static_data->last_debugged_alarm_time > watchdog_->start_time_) {
// False alarm: we started our clock before the debugger break (last
// alarm time).
watchdog_->start_time_ += static_data->last_debugged_alarm_delay;
if (static_data->last_debugged_alarm_time > watchdog_->start_time_)
// Too many alarms must have taken place.
watchdog_->state_ = DISARMED;
continue;
}
}
watchdog_->state_ = DISARMED; // Only alarm at most once.
TimeTicks last_alarm_time = TimeTicks::Now();
{
AutoUnlock unlock(watchdog_->lock_);
watchdog_->Alarm(); // Set a break point here to debug on alarms.
}
TimeDelta last_alarm_delay = TimeTicks::Now() - last_alarm_time;
if (last_alarm_delay <= TimeDelta::FromMilliseconds(2))
continue;
// Ignore race of two alarms/breaks going off at roughly the same time.
AutoLock static_lock(static_data->lock);
// This was a real debugger break.
static_data->last_debugged_alarm_time = last_alarm_time;
static_data->last_debugged_alarm_delay = last_alarm_delay;
}
}
void Watchdog::ThreadDelegate::SetThreadName() const {
std::string name = watchdog_->thread_watched_name_ + " Watchdog";
PlatformThread::SetName(name);
DVLOG(1) << "Watchdog active: " << name;
}
// static
void Watchdog::ResetStaticData() {
StaticData* static_data = GetStaticData();
AutoLock lock(static_data->lock);
// See https://crbug.com/734232 for why this cannot be zero-initialized.
static_data->last_debugged_alarm_time = TimeTicks::Min();
static_data->last_debugged_alarm_delay = TimeDelta();
}
} // namespace base
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