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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 "mongo/base/status_with.h"
#include "mongo/executor/task_executor.h"
namespace mongo {
namespace repl {
class Mutex;
/**
* The RollbackChecker maintains a sync source and its baseline rollback ID (rbid). It
* contains methods to check if a rollback occurred by checking if the rbid has changed since
* the baseline was set.
*
* To use the RollbackChecker:
* 1) Create a RollbackChecker by passing in an executor, and a sync source to use. If the
* sync source changes, make a new RollbackChecker.
* 2) Call reset(), either synchronously or asynchronously, so that the RollbackChecker retrieves
* the state it needs from the sync source to check for rollbacks.
* 3) Call checkForRollback(), passing in a 'nextAction' callback. This checks if there was a
* rollback at the sync source. If there is a rollback or another error, the 'nextAction'
* callback will be invoked. This error could be an UnrecoverableRollbackError, when there is a
* rollback.
* The only case where 'nextAction' is not called is when checkForRollback fails because the
* task executor is unable to schedule the remote replSetGetRBID command. In this case,
* checkForRollback() returns the error from executorTaskExecutor::scheduleRemoteCommand().
* Alternatively, call hasHadRollback() which synchronously checks for a rollback and returns
* true if any error occurs. Checking for a rollback does not reset the baseline rbid.
* 4) Repeat steps 2 and 3 as needed.
*
*/
class RollbackChecker {
RollbackChecker(const RollbackChecker&) = delete;
RollbackChecker& operator=(const RollbackChecker&) = delete;
public:
// Rollback checker result - true if rollback occurred; false if rollback IDs
// were the same; Otherwise, error status indicating why rollback check failed.
using Result = StatusWith<bool>;
using CallbackFn = stdx::function<void(const Result& result)>;
using RemoteCommandCallbackFn = executor::TaskExecutor::RemoteCommandCallbackFn;
using CallbackHandle = executor::TaskExecutor::CallbackHandle;
RollbackChecker(executor::TaskExecutor* executor, HostAndPort syncSource);
virtual ~RollbackChecker();
// Checks whether the the sync source has had a rollback since the last time reset was called,
// and then calls the nextAction with the rollback checker result. An error status
// will be passed to the callback if the RBID cannot be determined or if
// the callback was canceled.
StatusWith<CallbackHandle> checkForRollback(const CallbackFn& nextAction);
// Synchronously checks if there has been a rollback and returns a boolean specifying if one
// has occurred.
Result hasHadRollback();
// Resets the state used to decide if a rollback occurs, and then calls the nextAction with a
// status specifying what should occur next. The status will either be OK if there was no
// error or another status if the command failed. The nextAction should account for
// each of these cases.
StatusWith<CallbackHandle> reset(const CallbackFn& nextAction);
// Synchronously calls reset and returns the Status of the command.
Status reset_sync();
// Returns the current baseline rbid.
int getBaseRBID();
// ================== Test Support API ===================
// Returns the last rbid seen.
int getLastRBID_forTest();
private:
// Assumes a lock has been taken. Returns if a rollback has occurred by comparing the remoteRBID
// provided and the stored baseline rbid. Sets _lastRBID to the remoteRBID provided.
bool _checkForRollback_inlock(int remoteRBID);
// Schedules a remote command to get the rbid at the sync source and then calls the nextAction.
// If there is an error scheduling the call, it returns the error from
// TaskExecutor::scheduleRemoteCommand().
StatusWith<CallbackHandle> _scheduleGetRollbackId(const RemoteCommandCallbackFn& nextAction);
// Assumes a lock has been taken. Sets the current rbid used as the baseline for rollbacks.
void _setRBID_inlock(int rbid);
// Not owned by us.
executor::TaskExecutor* const _executor;
// Protects member data of this RollbackChecker.
mutable stdx::mutex _mutex;
// The sync source to check for rollbacks against.
HostAndPort _syncSource;
// The baseline rbid of the sync source to use when deciding if a rollback should occur.
int _baseRBID;
// The last rbid that we saw.
int _lastRBID;
};
} // namespace repl
} // namespace mongo
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