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/**
* Copyright (C) 2014 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 <stdlib.h>
#include <string>
#include "mongo/base/disallow_copying.h"
namespace mongo {
/**
* A RecoveryUnit is responsible for ensuring that data is persisted.
* All on-disk information must be mutated through this interface.
*/
class RecoveryUnit {
MONGO_DISALLOW_COPYING(RecoveryUnit);
public:
virtual ~RecoveryUnit() { }
/**
* These should be called through WriteUnitOfWork rather than directly.
*
* begin and end mark the begining and end of a unit of work. Each call to begin must be
* matched with exactly one call to end. commit can be called any number of times between
* begin and end but must not be called outside. When end() is called, all changes since the
* last commit (if any) will be rolled back.
*
* If UnitsOfWork nest (ie begin is called twice before a call to end), the prior paragraph
* describes the behavior of the outermost UnitOfWork. Inner UnitsOfWork neither commit nor
* rollback on their own but rely on the outermost to do it. If an inner UnitOfWork commits
* any changes, it is illegal for an outer unit to rollback. If an inner UnitOfWork
* rollsback any changes, it is illegal for an outer UnitOfWork to do anything other than
* rollback.
*
* The goal is not to fully support nested transaction, instead we want to allow delaying
* commit on a unit if it is part of a larger atomic unit.
*
* TODO see if we can get rid of nested UnitsOfWork.
*/
virtual void beginUnitOfWork() = 0;
virtual void commitUnitOfWork() = 0;
virtual void endUnitOfWork() = 0;
// WARNING: "commit" in functions below refers to a global journal flush which implicitly
// commits the current UnitOfWork as well. They are actually stronger than commitUnitOfWork
// as they can commit even if the UnitOfWork is nested. That is because we have already
// verified that the db will be left in a valid state at these commit points.
// TODO clean up the naming and semantics.
/**
* XXX: document
*/
virtual bool awaitCommit() = 0;
/**
* Commit if required. May take a long time. Returns true if committed.
*
* WARNING: Data *must* be in a crash-recoverable state when this is called.
*/
virtual bool commitIfNeeded(bool force = false) = 0;
/**
* Returns true if a global commit of the journal is needed but does not commit.
*/
virtual bool isCommitNeeded() const = 0;
//
// The remaining methods probably belong on DurRecoveryUnit rather than on the interface.
//
/**
* Declare that the data at [x, x + len) is being written.
*/
virtual void* writingPtr(void* data, size_t len) = 0;
/**
* Commits pending changes, flushes all changes to main data files, then removes the
* journal.
*
* WARNING: Data *must* be in a crash-recoverable state when this is called.
*
* This is useful as a "barrier" to ensure that writes before this call will never go
* through recovery and be applied to files that have had changes made after this call
* applied.
*/
virtual void syncDataAndTruncateJournal() = 0;
//
// Syntactic sugar
//
/**
* Declare write intent for an int
*/
inline int& writingInt(int& d) {
return *writing(&d);
}
/**
* A templated helper for writingPtr.
*/
template <typename T>
inline T* writing(T* x) {
writingPtr(x, sizeof(T));
return x;
}
protected:
RecoveryUnit() { }
};
class WriteUnitOfWork {
MONGO_DISALLOW_COPYING(WriteUnitOfWork);
public:
WriteUnitOfWork(RecoveryUnit* ru) : _ru(ru) { _ru->beginUnitOfWork(); }
~WriteUnitOfWork(){ _ru->endUnitOfWork(); }
void commit() { _ru->commitUnitOfWork(); }
RecoveryUnit* const _ru;
};
} // namespace mongo
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