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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kControl
#include "mongo/platform/basic.h"
#include "mongo/util/background_thread_clock_source.h"
#include <chrono>
#include <thread>
#include "mongo/stdx/memory.h"
#include "mongo/stdx/thread.h"
#include "mongo/util/concurrency/idle_thread_block.h"
#include "mongo/util/log.h"
#include "mongo/util/time_support.h"
namespace mongo {
BackgroundThreadClockSource::BackgroundThreadClockSource(std::unique_ptr<ClockSource> clockSource,
Milliseconds granularity)
: _clockSource(std::move(clockSource)), _granularity(granularity) {
_startTimerThread();
_tracksSystemClock = _clockSource->tracksSystemClock();
}
BackgroundThreadClockSource::~BackgroundThreadClockSource() {
{
stdx::unique_lock<stdx::mutex> lock(_mutex);
_inShutdown = true;
_condition.notify_one();
}
_timer.join();
}
Milliseconds BackgroundThreadClockSource::getPrecision() {
return _granularity;
}
Status BackgroundThreadClockSource::setAlarm(Date_t when, unique_function<void()> action) {
return _clockSource->setAlarm(when, std::move(action));
}
Date_t BackgroundThreadClockSource::now() {
// Since this is called very frequently by many threads, the common case should not write to
// shared memory.
if (MONGO_unlikely(_timerWillPause.load())) {
return _slowNow();
}
auto now = _current.load();
if (MONGO_unlikely(!now)) {
return _slowNow();
}
return Date_t::fromMillisSinceEpoch(now);
}
// This will be called at most once per _granularity per thread. In common cases it will only be
// called by a single thread per _granularity.
Date_t BackgroundThreadClockSource::_slowNow() {
_timerWillPause.store(false);
auto now = _current.load();
if (!now) {
stdx::lock_guard<stdx::mutex> lock(_mutex);
// Reload and check after locking since someone else may have done this for us.
now = _current.load();
if (!now) {
// Wake up timer but have it pause if no else calls now() for the next _granularity.
_condition.notify_one();
_timerWillPause.store(true);
now = _updateCurrent_inlock();
}
}
return Date_t::fromMillisSinceEpoch(now);
}
void BackgroundThreadClockSource::_startTimerThread() {
// Start the background thread that repeatedly sleeps for the specified duration of milliseconds
// and wakes up to store the current time.
_timer = stdx::thread([&]() {
setThreadName("BackgroundThreadClockSource");
stdx::unique_lock<stdx::mutex> lock(_mutex);
_started = true;
_condition.notify_one();
while (!_inShutdown) {
if (!_timerWillPause.swap(true)) {
_updateCurrent_inlock();
} else {
// Stop running if nothing has read the time since we last updated the time.
_current.store(0);
MONGO_IDLE_THREAD_BLOCK;
_condition.wait(lock, [this] { return _inShutdown || _current.load() != 0; });
}
const auto sleepUntil = Date_t::fromMillisSinceEpoch(_current.load()) + _granularity;
MONGO_IDLE_THREAD_BLOCK;
_clockSource->waitForConditionUntil(
_condition, lock, sleepUntil, [this] { return _inShutdown; });
}
});
// Wait for the thread to start. This prevents other threads from calling now() until the timer
// thread is at its first wait() call. While the code would work without this, it makes startup
// more predictable and therefore easier to test.
stdx::unique_lock<stdx::mutex> lock(_mutex);
_condition.wait(lock, [this] { return _started; });
}
int64_t BackgroundThreadClockSource::_updateCurrent_inlock() {
auto now = _clockSource->now().toMillisSinceEpoch();
if (!now) {
// We use 0 to indicate that the thread isn't running.
severe() << "ClockSource " << demangleName(typeid(*_clockSource)) << " reported time 0."
<< " Is it 1970?";
fassertFailed(40399);
}
_current.store(now);
return now;
}
} // namespace mongo
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