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/**
* Copyright (C) 2019-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.
*/
#pragma once
#include <map>
#include <memory>
#include <vector>
#include <boost/optional.hpp>
#include <boost/utility/in_place_factory.hpp>
#include "mongo/db/client_strand.h"
#include "mongo/db/repl/optime.h"
#include "mongo/db/service_context.h"
#include "mongo/executor/task_executor.h"
#include "mongo/platform/mutex.h"
#include "mongo/stdx/thread.h"
#include "mongo/util/concurrency/thread_pool.h"
#include "mongo/util/future.h"
namespace mongo {
namespace detail {
class AsyncConditionVariable {
public:
AsyncConditionVariable() : _current(boost::in_place()) {}
SemiFuture<void> onNotify() {
stdx::lock_guard lk(_mutex);
return _current->getFuture().semi();
}
void notifyAllAndReset() {
stdx::lock_guard lk(_mutex);
if (_inShutdown) {
return;
}
_current->emplaceValue();
_current = boost::in_place();
}
void notifyAllAndClose() {
stdx::lock_guard lk(_mutex);
if (_inShutdown) {
return;
}
_inShutdown = true;
_current->emplaceValue();
}
private:
mutable Mutex _mutex = MONGO_MAKE_LATCH("AsyncConditionVariable::_mutex");
boost::optional<SharedPromise<void>> _current;
bool _inShutdown{false};
};
} // namespace detail
class WaitForMajorityServiceImplBase {
public:
virtual ~WaitForMajorityServiceImplBase();
void startup(ServiceContext* ctx);
void shutDown();
SemiFuture<void> waitUntilMajority(const repl::OpTime& opTime,
const CancellationToken& cancelToken);
private:
enum class State { kNotStarted, kRunning, kShutdown };
// State is kNotStarted on construction, kRunning after WaitForMajorityService::startup() has
// been called, and kShutdown after WaitForMajorityService::shutdown() has been called. It is
// illegal to call WaitForMajorityService::waitUntilMajority before calling startup.
State _state{State::kNotStarted};
/**
* Internal representation of an individual request to wait on some particular optime.
*/
struct Request {
explicit Request(Promise<void> promise)
: hasBeenProcessed{false}, result(std::move(promise)) {}
AtomicWord<bool> hasBeenProcessed;
Promise<void> result;
};
using OpTimeWaitingMap = std::multimap<repl::OpTime, std::shared_ptr<Request>>;
/**
* Periodically checks the list of opTimes to wait for majority committed.
*/
SemiFuture<void> _periodicallyWaitForMajority();
virtual Status _waitForOpTime(OperationContext* opCtx, const repl::OpTime& opTime) = 0;
virtual StringData _getReadOrWrite() const = 0;
// The pool of threads available to wait on opTimes and cancel existing requests.
std::shared_ptr<ThreadPool> _pool;
// This future is completed when the service has finished all of its work and is ready for
// shutdown.
boost::optional<SemiFuture<void>> _backgroundWorkComplete;
// Manages the Client responsible for the thread that waits on opTimes.
ClientStrandPtr _waitForMajorityClient;
// Manages the Client responsible for the thread that cancels existing requests to wait on
// opTimes.
ClientStrandPtr _waitForMajorityCancellationClient;
// This mutex synchronizes access to the members declared below.
Mutex _mutex = MONGO_MAKE_LATCH("WaitForMajorityService::_mutex");
// Contains an ordered list of opTimes to wait to be majority comitted.
OpTimeWaitingMap _queuedOpTimes;
// Contains the last opTime that the background thread was able to successfully wait to be
// majority comitted.
repl::OpTime _lastOpTimeWaited;
// Use for signalling new opTime requests being queued.
detail::AsyncConditionVariable _hasNewOpTimeCV;
};
class WaitForMajorityServiceForReadImpl : public WaitForMajorityServiceImplBase {
private:
Status _waitForOpTime(OperationContext* opCtx, const repl::OpTime& opTime) final;
StringData _getReadOrWrite() const final {
return "Read"_sd;
}
};
class WaitForMajorityServiceForWriteImpl : public WaitForMajorityServiceImplBase {
private:
Status _waitForOpTime(OperationContext* opCtx, const repl::OpTime& opTime) final;
StringData _getReadOrWrite() const final {
return "Write"_sd;
}
};
/**
* Provides a facility for asynchronously waiting a local opTime to be majority committed.
*/
class WaitForMajorityService {
public:
~WaitForMajorityService();
static WaitForMajorityService& get(ServiceContext* service);
/**
* Sets up the background thread pool responsible for waiting for opTimes to be majority
* committed.
*/
void startup(ServiceContext* ctx);
/**
* Blocking method, which shuts down and joins the background thread.
*/
void shutDown();
/**
* Identical to waitUntilMajorityForWrite, which should be used instead.
*
* TODO(SERVER-74754): Remove this method and replace all uses with waitUntilMajorityForWrite.
*/
SemiFuture<void> waitUntilMajority(const repl::OpTime& opTime,
const CancellationToken& cancelToken);
/**
* Enqueue a request to wait for the given opTime to be majority committed.
*/
SemiFuture<void> waitUntilMajorityForRead(const repl::OpTime& opTime,
const CancellationToken& cancelToken);
/**
* Enqueue a request to wait for the given opTime to be majority committed on this primary.
* Returns a PrimarySteppedDown error if the primary steps down while waiting or if this is
* a secondary.
*/
SemiFuture<void> waitUntilMajorityForWrite(const repl::OpTime& opTime,
const CancellationToken& cancelToken);
private:
WaitForMajorityServiceForReadImpl _readService;
WaitForMajorityServiceForWriteImpl _writeService;
};
} // namespace mongo
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