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/**
* Copyright (C) 2015 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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 <boost/thread/mutex.hpp>
#include <string>
#include <vector>
#include "mongo/base/disallow_copying.h"
#include "mongo/base/status.h"
#include "mongo/base/status_with.h"
#include "mongo/bson/bsonobj.h"
#include "mongo/db/clientcursor.h"
#include "mongo/db/repl/replication_executor.h"
#include "mongo/stdx/functional.h"
#include "mongo/util/net/hostandport.h"
namespace mongo {
namespace repl {
class Fetcher {
MONGO_DISALLOW_COPYING(Fetcher);
public:
/**
* Container for BSON documents extracted from find and getMore command results.
*/
typedef std::vector<BSONObj> Documents;
/**
* Documents in current batch with cursor ID.
* If cursor ID is zero, there will be no additional batches.
*/
struct BatchData {
BatchData();
BatchData(CursorId theCursorId, Documents theDocuments);
CursorId cursorId;
Documents documents;
};
/**
* Represents next steps of fetcher.
*/
enum class NextAction {
kInvalid=0,
kNoAction=1,
kContinue=2
};
/**
* Type of a fetcher callback function.
*/
typedef stdx::function<void (const StatusWith<BatchData>&, NextAction*)> CallbackFn;
/**
* Creates Fetcher task but does not schedule it to be run by the executor.
*
* Callback function 'work' will be called 1 or more times after a successful
* schedule() call depending on the results of the query.
*
* Depending on the query in the initial find command object, the fetcher may run
* subsequent getMore commands on the remote server in order to obtain a complete
* set of results for the query.
*
* Failed find or getMore commands will also cause 'work' to be invoked with the
* error details provided by the remote server. On failure, the fetcher will stop
* sending getMore requests to the remote server.
*
* If the fetcher is canceled (either by calling cancel() or shutting down the executor),
* 'work' will not be invoked.
*
* Fetcher uses the NextAction argument to inform client via callback if a getMore command
* will be scheduled to be run by the executor to retrieve additional results.
* Also, note that the NextAction is both an input and output argument to allow
* the client to suggest a different action for the fetcher to take post-callback.
*
* The callback function 'work' is not allowed to call into the Fetcher instance. This
* behavior is undefined and may result in a deadlock.
*/
Fetcher(ReplicationExecutor* executor,
const HostAndPort& target,
const std::string& dbname,
const BSONObj& findCmdObj,
const CallbackFn& work);
virtual ~Fetcher();
/**
* Returns diagnostic information.
*/
std::string getDiagnosticString() const;
/**
* Returns true if a find or getMore has been scheduled (but not completed)
* with the executor.
*/
bool isActive() const;
/**
* Schedules query to be run on the remote server.
*/
Status schedule();
/**
* Cancels current find or getMore request.
* Returns immediately if fetcher is not active.
*/
void cancel();
/**
* Waits for active find or getMore request to complete.
* Returns immediately if fetcher is not active.
*/
void wait();
private:
/**
* Schedules find or getMore command to be run by the executor
*/
Status _schedule_inlock(const BSONObj& cmdObj, const char* batchFieldName);
/**
* Callback for both find and getMore remote command.
*/
void _callback(const ReplicationExecutor::RemoteCommandCallbackData& rcbd,
const char* batchFieldName);
// Not owned by us.
ReplicationExecutor* _executor;
HostAndPort _target;
std::string _dbname;
BSONObj _findCmdObj;
CallbackFn _work;
// Protects member data of this Fetcher.
mutable boost::mutex _mutex;
// _active is true when Fetcher is scheduled to be run by the executor.
bool _active;
// Callback handle to the scheduled remote command.
ReplicationExecutor::CallbackHandle _remoteCommandCallbackHandle;
};
} // namespace repl
} // namespace mongo
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