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/* Copyright 2013 10gen Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#pragma once
#include <boost/scoped_ptr.hpp>
#include <boost/thread/mutex.hpp>
#include <iostream>
#include <string>
#include "mongo/base/disallow_copying.h"
#include "mongo/base/status.h"
namespace mongo {
namespace logger {
/**
* A synchronized file output stream writer, with support for file rotation.
*
* To enforce proper locking, instances of RotatableFileWriter may only be manipulated by
* instantiating a RotatableFileWriter::Use guard object, which exposes the relevant
* manipulation methods for the stream. For any instance of RotatableFileWriter, at most one
* fully constructed instance of RotatableFileWriter::Use exists at a time, providing mutual
* exclusion.
*
* Behavior is undefined if two instances of RotatableFileWriter should simultaneously have the
* same value for their fileName.
*/
class RotatableFileWriter {
MONGO_DISALLOW_COPYING(RotatableFileWriter);
public:
/**
* Guard class representing synchronous use of an instance of RotatableFileWriter.
*/
class Use {
MONGO_DISALLOW_COPYING(Use);
public:
/**
* Constructs a Use object for "writer", and lock "writer".
*/
explicit Use(RotatableFileWriter* writer);
/**
* Sets the name of the target file to which stream() writes to "name".
*
* May be called repeatedly.
*
* If this method does not return Status::OK(), it is not safe to call rotate() or
* stream().
*
* Set "append" to true to open "name" in append mode. Otherwise, it is truncated.
*/
Status setFileName(const std::string& name, bool append);
/**
* Rotates the currently opened file into "renameTarget", and open a new file
* with the name previously set via setFileName().
*
* Returns Status::OK() on success. If the rename fails, returns
* ErrorCodes::FileRenameFailed, and the stream continues to write to the unrotated
* file. If the rename succeeds but the subsequent file open fails, returns
* ErrorCodes::FileNotOpen, and the stream continues to target the original file, though
* under its new name.
*/
Status rotate(const std::string& renameTarget);
/**
* Returns the status of the stream.
*
* One of Status::OK(), ErrorCodes::FileNotOpen and ErrorCodes::FileStreamFailed.
*/
Status status();
/**
* Returns a reference to the std::ostream() through which users may write to the file.
*/
std::ostream& stream() { return *_writer->_stream; }
private:
/**
* Helper that opens the file named by setFileName(), in the mode specified by "append".
*
* Returns Status::OK() on success and ErrorCodes::FileNotOpen on failure.
*/
Status _openFileStream(bool append);
RotatableFileWriter* _writer;
boost::unique_lock<boost::mutex> _lock;
};
/**
* Constructs an instance of RotatableFileWriter.
*/
RotatableFileWriter();
private:
friend class RotatableFileWriter::Use;
boost::mutex _mutex;
std::string _fileName;
boost::scoped_ptr<std::ostream> _stream;
};
} // namespace logger
} // namespace mongo
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