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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 <boost/optional.hpp>
#include "mongo/bson/bsonobj.h"
#include "mongo/util/future.h"
namespace mongo {
/**
* Implements the critical section logic for particular collection or database in the sharding
* subsystem. It supports two phases - catch-up and commit. During the catch-up phase, only writes
* are disallowed, but reads can still proceed. In the commit phase, both reads and writes are
* disallowed.
*
* Currently, only collections stay in the catch-up phase while the last batch of mods is
* transferred to the recipient shard. Databases effectively only support the commit phase.
*/
class ShardingMigrationCriticalSection {
ShardingMigrationCriticalSection(const ShardingMigrationCriticalSection&) = delete;
ShardingMigrationCriticalSection& operator=(const ShardingMigrationCriticalSection&) = delete;
public:
ShardingMigrationCriticalSection();
~ShardingMigrationCriticalSection();
/**
* Enters the critical section in a mode, which still allows reads.
*
* NOTE: Must be called under the appropriate X lock (collection or database).
*/
void enterCriticalSectionCatchUpPhase(const BSONObj& reason);
/**
* Sets the critical section in a mode, which disallows reads.
*/
void enterCriticalSectionCommitPhase(const BSONObj& reason);
/**
* Leaves the critical section.
*/
void exitCriticalSection(const BSONObj& reason);
/**
* Leaves the critical section without doing error-checking. Only meant to be used when
* recovering the critical sections in the RecoverableCriticalSectionService.
*/
void exitCriticalSectionNoChecks();
/**
* Sets the critical section back to the catch up phase, which disallows reads.
*/
void rollbackCriticalSectionCommitPhaseToCatchUpPhase(const BSONObj& reason);
/**
* Retrieves a critical section future to wait on. Will return boost::none if the migration is
* not yet in the critical section or if the caller is a reader and the migration is not yet in
* the commit phase.
*/
enum Operation { kRead, kWrite };
boost::optional<SharedSemiFuture<void>> getSignal(Operation op) const;
boost::optional<BSONObj> getReason() const;
private:
struct CriticalSectionContext {
CriticalSectionContext(BSONObj reason_) : reason(std::move(reason_)) {}
// Whether the migration source is in a critical section. Tracked as a shared promise so
// that callers don't have to hold metadata locks in order to wait on it.
SharedPromise<void> critSecSignal;
// Used to delay blocking reads up until the commit of the metadata on the config server
// needs to happen. This allows the shard to serve reads up until the config server metadata
// update needs to be committed.
//
// The transition from false to true is protected by the database or collection X-lock,
// which happens just before the config server metadata commit is scheduled.
bool readsShouldWaitOnCritSec{false};
// Information about the operation that originally acquired the critical section. Used to
// make the operations that modify the state of the CS idempotent and to provide more
// detailed error messages.
BSONObj reason;
};
boost::optional<CriticalSectionContext> _critSecCtx;
};
} // namespace mongo
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