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/**
* Copyright (C) 2016 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/optional.hpp>
#include "mongo/base/disallow_copying.h"
#include "mongo/s/move_chunk_request.h"
#include "mongo/stdx/memory.h"
#include "mongo/stdx/mutex.h"
#include "mongo/util/concurrency/notification.h"
namespace mongo {
class OperationContext;
class ScopedRegisterMigration;
template <typename T>
class StatusWith;
/**
* Thread-safe object, which keeps track of the active migrations running on a node and limits them
* to only one per-shard. There is only one instance of this object per shard.
*/
class ActiveMigrationsRegistry {
MONGO_DISALLOW_COPYING(ActiveMigrationsRegistry);
public:
ActiveMigrationsRegistry();
~ActiveMigrationsRegistry();
/**
* If there are no migrations running on this shard, registers an active migration with the
* specified arguments and returns a ScopedRegisterMigration, which must be signaled by the
* caller before it goes out of scope.
*
* If there is an active migration already running on this shard and it has the exact same
* arguments, returns a ScopedRegisterMigration, which can be used to join the already running
* migration.
*
* Otherwise returns a ConflictingOperationInProgress error.
*/
StatusWith<ScopedRegisterMigration> registerMigration(const MoveChunkRequest& args);
/**
* If a migration has been previously registered through a call to registerMigration returns
* that namespace. Otherwise returns boost::none.
*/
boost::optional<NamespaceString> getActiveMigrationNss();
/**
* Returns a report on the active migration if there currently is one. Otherwise, returns an
* empty BSONObj.
*
* Takes an IS lock on the namespace of the active migration, if one is active.
*/
BSONObj getActiveMigrationStatusReport(OperationContext* txn);
private:
friend class ScopedRegisterMigration;
// Describes the state of a currently active moveChunk operation
struct ActiveMoveChunkState {
ActiveMoveChunkState(MoveChunkRequest inArgs)
: args(std::move(inArgs)), notification(std::make_shared<Notification<Status>>()) {}
// Exact arguments of the currently active operation
MoveChunkRequest args;
// Notification event, which will be signaled when the currently active operation completes
std::shared_ptr<Notification<Status>> notification;
};
/**
* Unregisters a previously registered namespace with ongoing migration. Must only be called if
* a previous call to registerMigration has succeeded.
*/
void _clearMigration();
// Protects the state below
stdx::mutex _mutex;
// If there is an active moveChunk operation going on, this field contains the request, which
// initiated it
boost::optional<ActiveMoveChunkState> _activeMoveChunkState;
};
/**
* Object of this class is returned from the registerMigration call of the active migrations
* registry. It can exist in two modes - 'unregister' and 'join'. See the comments for
* registerMigration method for more details.
*/
class ScopedRegisterMigration {
MONGO_DISALLOW_COPYING(ScopedRegisterMigration);
public:
ScopedRegisterMigration(ActiveMigrationsRegistry* registry,
bool forUnregister,
std::shared_ptr<Notification<Status>> completionNotification);
~ScopedRegisterMigration();
ScopedRegisterMigration(ScopedRegisterMigration&&);
ScopedRegisterMigration& operator=(ScopedRegisterMigration&&);
/**
* Returns true if the migration object is in the 'unregister' mode, which means that the holder
* must execute the moveChunk command and complete with a status.
*/
bool mustExecute() const {
return _forUnregister;
}
/**
* Must only be called if the object is in the 'unregister' mode. Signals any callers, which
* might be blocked in waitForCompletion.
*/
void complete(Status status);
/**
* Must only be called if the object is in the 'join' mode. Blocks until the main executor of
* the moveChunk command calls complete.
*/
Status waitForCompletion(OperationContext* txn);
private:
// Registry from which to unregister the migration. Not owned.
ActiveMigrationsRegistry* _registry;
// Whether this is a newly started migration (in which case the destructor must unregister) or
// joining an existing one (in which case the caller must wait for completion).
bool _forUnregister;
// This is the future, which will be signaled at the end of a migration
std::shared_ptr<Notification<Status>> _completionNotification;
};
} // namespace mongo
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