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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.
*/
#pragma once
#include <atomic>
#include <functional>
#include <memory>
#include "mongo/base/status.h"
#include "mongo/config.h"
#include "mongo/db/client.h"
#include "mongo/db/service_context.h"
#include "mongo/platform/atomic_word.h"
#include "mongo/platform/mutex.h"
#include "mongo/stdx/thread.h"
#include "mongo/transport/message_compressor_base.h"
#include "mongo/transport/service_entry_point.h"
#include "mongo/transport/service_executor.h"
#include "mongo/transport/session.h"
#include "mongo/transport/transport_mode.h"
#include "mongo/util/future.h"
#include "mongo/util/net/ssl_manager.h"
namespace mongo {
namespace transport {
/*
* The ServiceStateMachine holds the state of a single client connection and represents the
* lifecycle of each user request as a state machine. It is the glue between the stateless
* ServiceEntryPoint and TransportLayer that ties network and database logic together for a
* user.
*/
class ServiceStateMachine : public std::enable_shared_from_this<ServiceStateMachine> {
ServiceStateMachine(ServiceStateMachine&) = delete;
ServiceStateMachine& operator=(ServiceStateMachine&) = delete;
public:
ServiceStateMachine(ServiceStateMachine&&) = delete;
ServiceStateMachine& operator=(ServiceStateMachine&&) = delete;
/*
* Construct a ServiceStateMachine for a given Client.
*/
ServiceStateMachine(ServiceContext::UniqueClient client);
/*
* Any state may transition to EndSession in case of an error, otherwise the valid state
* transitions are:
* Source -> SourceWait -> Process -> SinkWait -> Source (standard RPC)
* Source -> SourceWait -> Process -> SinkWait -> Process -> SinkWait ... (exhaust)
* Source -> SourceWait -> Process -> Source (fire-and-forget)
*/
enum class State {
Created, // The session has been created, but no operations have been performed yet
Source, // Request a new Message from the network to handle
SourceWait, // Wait for the new Message to arrive from the network
Process, // Run the Message through the database
SinkWait, // Wait for the database result to be sent by the network
EndSession, // End the session - the ServiceStateMachine will be invalid after this
Ended // The session has ended. It is illegal to call any method besides
// state() if this is the current state.
};
/*
* When start() is called with Ownership::kOwned, the SSM will swap the Client/thread name
* whenever it runs a stage of the state machine, and then unswap them out when leaving the SSM.
*
* With Ownership::kStatic, it will assume that the SSM will only ever be run from one thread,
* and that thread will not be used for other SSM's. It will swap in the Client/thread name
* for the first run and leave them in place.
*
* kUnowned is used internally to mark that the SSM is inactive.
*/
enum class Ownership { kUnowned, kOwned, kStatic };
/*
* start() schedules a call to _runOnce() in the future.
*/
void start();
/*
* Gets the current state of connection for testing/diagnostic purposes.
*/
State state();
/*
* Terminates the associated transport Session, regardless of tags.
*
* This will not block on the session terminating cleaning itself up, it returns immediately.
*/
void terminate();
/*
* Terminates the associated transport Session if its tags don't match the supplied tags.
* If the session is in a pending state, before any tags have been set, it will not be
* terminated.
*
* This will not block on the session terminating cleaning itself up, it returns immediately.
*/
void terminateIfTagsDontMatch(transport::Session::TagMask tags);
/*
* Sets a function to be called after the session is ended
*/
void setCleanupHook(std::function<void()> hook);
private:
/*
* A class that wraps up lifetime management of the _dbClient and _threadName for
* each step in _runOnce();
*/
class ThreadGuard;
friend class ThreadGuard;
/*
* Terminates the associated transport Session if status indicate error.
*
* This will not block on the session terminating cleaning itself up, it returns immediately.
*/
void _terminateAndLogIfError(Status status);
/*
* This is a helper function to schedule tasks on the serviceExecutor maintaining a shared_ptr
* copy to anchor the lifetime of the SSM while waiting for callbacks to run.
*
* If scheduling the function fails, the SSM will be terminated and cleaned up immediately
*/
void _scheduleNextWithGuard(ThreadGuard guard,
transport::ServiceExecutor::ScheduleFlags flags,
Ownership ownershipModel = Ownership::kOwned);
/*
* Gets the transport::Session associated with this connection
*/
const transport::SessionHandle& _session() const;
/*
* Gets the transport::ServiceExecutor associated with this connection.
*/
ServiceExecutor* _executor();
/*
* This function actually calls into the database and processes a request. It's broken out
* into its own inline function for better readability.
*/
Future<void> _processMessage(ThreadGuard guard);
/*
* These get called by the TransportLayer when requested network I/O has completed.
*/
void _sourceCallback(Status status);
void _sinkCallback(Status status);
/*
* Source/Sink message from the TransportLayer. These will invalidate the ThreadGuard just
* before waiting on the TL.
*/
Future<void> _sourceMessage(ThreadGuard guard);
Future<void> _sinkMessage(ThreadGuard guard);
/*
* Releases all the resources associated with the session and call the cleanupHook.
*/
void _cleanupSession(ThreadGuard guard);
/*
* This is the initial function called at the beginning of a thread's lifecycle in the
* TransportLayer.
*/
void _runOnce();
/*
* Releases all the resources associated with the exhaust request.
*/
void _cleanupExhaustResources() noexcept;
AtomicWord<State> _state{State::Created};
ServiceContext* const _serviceContext;
ServiceEntryPoint* const _sep;
transport::SessionHandle _sessionHandle;
ServiceContext::UniqueClient _dbClient;
Client* _dbClientPtr;
std::function<void()> _cleanupHook;
bool _inExhaust = false;
boost::optional<MessageCompressorId> _compressorId;
Message _inMessage;
Message _outMessage;
// Allows delegating destruction of opCtx to another function to potentially remove its cost
// from the critical path. This is currently only used in `_processMessage()`.
ServiceContext::UniqueOperationContext _killedOpCtx;
AtomicWord<Ownership> _owned{Ownership::kUnowned};
#if MONGO_CONFIG_DEBUG_BUILD
AtomicWord<stdx::thread::id> _owningThread;
#endif
};
template <typename T>
T& operator<<(T& stream, const ServiceStateMachine::State& state) {
switch (state) {
case ServiceStateMachine::State::Created:
stream << "created";
break;
case ServiceStateMachine::State::Source:
stream << "source";
break;
case ServiceStateMachine::State::SourceWait:
stream << "sourceWait";
break;
case ServiceStateMachine::State::Process:
stream << "process";
break;
case ServiceStateMachine::State::SinkWait:
stream << "sinkWait";
break;
case ServiceStateMachine::State::EndSession:
stream << "endSession";
break;
case ServiceStateMachine::State::Ended:
stream << "ended";
break;
}
return stream;
}
} // namespace transport
} // namespace mongo
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