// @file file_allocator.h

/*    Copyright 2009 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.
 */

#include "mongo/pch.h"

#include <list>
#include <boost/filesystem/path.hpp>
#include <boost/thread/condition.hpp>

namespace mongo {

    /*
     * Handles allocation of contiguous files on disk.  Allocation may be
     * requested asynchronously or synchronously.
     * singleton
     */
    class FileAllocator : boost::noncopyable {
        /*
         * The public functions may not be called concurrently.  The allocation
         * functions may be called multiple times per file, but only the first
         * size specified per file will be used.
        */
    public:
        void start();

        /**
         * May be called if file exists. If file exists, or its allocation has
         *  been requested, size is updated to match existing file size.
         */
        void requestAllocation( const string &name, long &size );


        /**
         * Returns when file has been allocated.  If file exists, size is
         * updated to match existing file size.
         */
        void allocateAsap( const string &name, unsigned long long &size );

        void waitUntilFinished() const;
        
        bool hasFailed() const;

        static void ensureLength(int fd, long size);

        /** @return the singleton */
        static FileAllocator * get();
        
    private:

        FileAllocator();

        void checkFailure();

        // caller must hold pendingMutex_ lock.  Returns size if allocated or
        // allocation requested, -1 otherwise.
        long prevSize( const string &name ) const;

        // caller must hold pendingMutex_ lock.
        bool inProgress( const string &name ) const;

        /** called from the worked thread */
        static void run( FileAllocator * fa );

        // generate a unique name for temporary files
        string makeTempFileName( boost::filesystem::path root );

        mutable mongo::mutex _pendingMutex;
        mutable boost::condition _pendingUpdated;

        std::list< string > _pending;
        mutable map< string, long > _pendingSize;

        // unique number for temporary files
        static unsigned long long _uniqueNumber;

        bool _failed;

        static FileAllocator* _instance;

    };

} // namespace mongo