FileAllocator.h

// -*- c++ -*-

#ifndef __FILE_ALLOCATOR_H__
#define __FILE_ALLOCATOR_H__

// system
#include <stdio.h>

// storage
#include "storage/StorageTypes.h"


class FileAllocator
{
public:

    FileAllocator();

    ~FileAllocator();
    
    bool attach(FILE *f, FileOffset reserved_space, bool init);

    FILE *getFile() const;
    
    void detach();

    FileOffset allocate(FileOffset num_bytes);

    FileOffset size() const
    {   return file_size; }
    
    void free(FileOffset offset);

    static FileOffset minimum_size;

    static FileOffset file_size_increment;
    
    bool dump(int level=1, FILE *out=stdout);
    
private:

    PROHIBIT_DEFAULT_COPY(FileAllocator);

    class Node
    {
    public:
        Node();
        
        static FileOffset size()
        {   return 12; }

        FileOffset getNext() const
        {   return next; }

        void setNext(FileOffset new_next)
        {   next = new_next; }

        FileOffset getPrev() const
        {   return prev; }

        void setPrev(FileOffset new_prev)
        {   prev = new_prev; }

        FileOffset getBytes() const
        {   return bytes; }

        void setBytes(FileOffset new_bytes)
        {   bytes = new_bytes; }

        void addBytes(int bytes_to_add);

        void read(FILE *f, FileOffset offset);
        
        void write(FILE *f, FileOffset offset) const;
        
        void write() const;
        
        FileOffset getOffset() const
        {   return offset; }

    private:
        mutable FILE *f;
        mutable FileOffset offset;
        FileOffset prev;
        FileOffset next;
        FileOffset bytes;
    };
    
    FILE *f;
    FileOffset reserved_space; // Bytes we ignore in header
    FileOffset file_size; // Total # of bytes in file
    // For the head nodes,
    // 'prev' = last entry, tail of list,
    // 'next' = first entry, head of list!
    // ! These nodes are always a current copy
    //   of what's on the disk!
    Node allocated_head, free_head;
    
    // Unlink node from list, node itself remains unchanged
    void remove_node(Node &head, const Node &node);
    // Insert node (sorted), node's prev/next get changed
    void insert_node(Node &head,
                     FileOffset node_offset, Node &node);
};


#endif