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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 <boost/optional.hpp>
#include <vector>
#include "mongo/base/status_with.h"
#include "mongo/bson/bsonobj.h"
#include "mongo/db/cursor_id.h"
#include "mongo/db/logical_session_id.h"
#include "mongo/db/namespace_string.h"
#include "mongo/executor/remote_command_request.h"
#include "mongo/executor/task_executor.h"
#include "mongo/util/duration.h"
#include "mongo/util/net/hostandport.h"
#include "mongo/util/producer_consumer_queue.h"
namespace mongo {
namespace executor {
/**
* A synchronous cursor API for managing a remote cursor that uses an async task executor to run all
* stages of the command cursor protocol (initial command, getMore, killCursors)
*
* The main differentiator for this type over DBClientCursor is the use of a task executor (which
* provides access to a different connection pool, as well as interruptibility) and the ability to
* overlap getMores. This starts fetching the next batch as soon as one is exhausted (rather than
* on a call to getNext()).
*/
class TaskExecutorCursor {
public:
// Cursor id has 1 of 3 states.
// <0 - We haven't yet received a response for our initial request
// 0 - Cursor is done (errored or consumed)
// >=1 - Cursor is live on the remote
constexpr static CursorId kUnitializedCursorId = -1;
constexpr static CursorId kClosedCursorId = 0;
constexpr static CursorId kMinLegalCursorId = 1;
struct Options {
boost::optional<int64_t> batchSize;
};
/**
* Construct the cursor with a RemoteCommandRequest wrapping the initial command
*
* One value is carried over in successive calls to getMore/killCursor:
*
* opCtx - The Logical Session Id from the initial command is carried over in all later stages.
* NOTE - the actual command must not include the lsid
*/
explicit TaskExecutorCursor(executor::TaskExecutor* executor,
const RemoteCommandRequest& rcr,
Options&& options = {});
/**
* Asynchronously kills async ops and kills the underlying cursor on destruction.
*/
~TaskExecutorCursor();
/**
* Returns the next document from this cursor until the cursor is exhausted (in which case we
* return an unset optional). This method can throw if there is an error running any commands,
* if the remote server returns a not ok command result, or if the passed in opCtx is
* interrupted (by killOp or maxTimeMS).
*
* The opCtx may also be used as the source of client metadata if this call to getNext()
* triggers a new getMore to fetch the next batch.
*/
boost::optional<BSONObj> getNext(OperationContext* opCtx);
const CursorId getCursorId() const {
return _cursorId;
}
Milliseconds resetWaitingTime() {
auto toRet = _millisecondsWaiting;
_millisecondsWaiting = Milliseconds(0);
return toRet;
}
private:
/**
* Runs a remote command and pipes the output back to this object
*/
void _runRemoteCommand(const RemoteCommandRequest& rcr);
/**
* Gets the next batch with interruptibility via the opCtx
*/
void _getNextBatch(OperationContext* opCtx);
/**
* Create a new request, annotating with lsid and current opCtx
*/
const RemoteCommandRequest& _createRequest(OperationContext* opCtx, const BSONObj& cmd);
executor::TaskExecutor* _executor;
// Used as a scratch pad for the successive scheduleRemoteCommand calls
RemoteCommandRequest _rcr;
const Options _options;
// If the opCtx is in our initial request, re-use it for all subsequent operations
boost::optional<LogicalSessionId> _lsid;
// Stash the callbackhandle for the current outstanding operation
boost::optional<TaskExecutor::CallbackHandle> _cbHandle;
CursorId _cursorId = kUnitializedCursorId;
// This is a sum of the time spent waiting on remote calls.
Milliseconds _millisecondsWaiting = Milliseconds(0);
// Namespace after we resolved the initial request
NamespaceString _ns;
// Storage for the last batch we fetched
std::vector<BSONObj> _batch;
decltype(_batch)::iterator _batchIter;
// Multi producer because we hold onto the producer side in this object, as well as placing it
// into callbacks for the task executor
MultiProducerSingleConsumerQueue<StatusWith<BSONObj>>::Pipe _pipe;
};
} // namespace executor
} // namespace mongo
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