disk.java

操作系统课内实验部分

import java.util.*;
import java.io.*;

class Disk {
    // the size in bytes of each disk block
    public final static int BLOCK_SIZE = 512;
    // the number of disk blocks in the system
    public final static int NUM_BLOCKS = 1000;

    // the number of pointers in a disk block to other disk blocks
    public final static int POINTERS_PER_BLOCK = (BLOCK_SIZE/4);

    // the number of reads and writes to the file system
    private int readCount = 0;
	private int writeCount = 0;

	// the file representing the simulated  disk
	private File fileName;
	private RandomAccessFile disk;

	// read in the file representing the simulated disk
	public Disk() {
		try {
			fileName = new File("DISK");
			disk = new RandomAccessFile(fileName, "rw");
		}
		catch (IOException e) {
			System.err.println ("Unable to start the disk");
			System.exit(1);
		}
	}

	private void seek(int blocknum) throws IOException {
		if (blocknum < 0 || blocknum >= NUM_BLOCKS) 
			throw new RuntimeException ("Attempt to read block " +
					       blocknum + " is out of range");
		disk.seek((long)(blocknum * BLOCK_SIZE));
	}

	/**
 	 * read from blockNum into a byte buffer
	 */
	public void read(int blocknum, byte[] buffer) {
		if (buffer.length != BLOCK_SIZE) 
			throw new RuntimeException(
				"Read: bad buffer size " + buffer.length);
		try {
			seek(blocknum);
			disk.read(buffer);
		}
		catch (IOException e) {
			System.err.println(e);
			System.exit(1);
		}
		readCount++;
	} 

	public void read(int blocknum, SuperBlock block) {
		try {
			seek(blocknum);
			block.size = disk.readInt();
			block.iSize = disk.readInt();
			block.freeList = disk.readInt();
		}
		catch (EOFException e) {
			if (blocknum != 0) {
				System.err.println(e);
				System.exit(1);
			}
			block.size = block.iSize = block.freeList = 0;
		}
		catch (IOException e) {
			System.err.println(e);
			System.exit(1);
		}
		readCount++;
	} 

	public void read(int blocknum, InodeBlock block) {
		try {
			seek(blocknum);
			for (int i=0; i<block.node.length; i++) {
				block.node[i].flags = disk.readInt();
				block.node[i].owner = disk.readInt();
				//block.node[i].size = disk.readInt();
				block.node[i].fileSize = disk.readInt();
				for (int j=0; j<13; j++)
					block.node[i].pointer[j] = disk.readInt();
			}
		}
		catch (IOException e) {
			System.err.println(e);
			System.exit(1);
		}
		readCount++;
	} 
		
	public void read(int blocknum, IndirectBlock block) {
		try {
			seek(blocknum);
			for (int i=0; i<block.pointer.length; i++)
				block.pointer[i] = disk.readInt();
		}
		catch (IOException e) {
			System.err.println(e);
			System.exit(1);
		}
		readCount++;
	} 
	
	/** 
	 * Write from the buffer to to blockNum 	
	 */
	public void write(int blocknum, byte[] buffer) {
		if (buffer.length != BLOCK_SIZE) 
			throw new RuntimeException(
				"Write: bad buffer size " + buffer.length);
		try {
			seek(blocknum);
			disk.write(buffer);
		}
		catch (IOException e) {
			System.err.println(e);
			System.exit(1);
		}
		writeCount++;
	}

	public void write(int blocknum, SuperBlock block) {
		try {
			seek(blocknum);
			disk.writeInt(block.size);
			disk.writeInt(block.iSize);
			disk.writeInt(block.freeList);
		}
		catch (IOException e) {
			System.err.println(e);
			System.exit(1);
		}
		writeCount++;
	} 

	public void write(int blocknum, InodeBlock block) {
		try {
			seek(blocknum);
			for (int i=0; i<block.node.length; i++) {
				disk.writeInt(block.node[i].flags);
				//disk.writeInt(block.node[i].owner);
				//disk.writeInt(block.node[i].size);
				disk.writeInt(block.node[i].fileSize);
				for (int j=0; j<13; j++)
					disk.writeInt(block.node[i].pointer[j]);
			}
		}
		catch (IOException e) {
			System.err.println(e);
			System.exit(1);
		}
		writeCount++;
	} 
		
	public void write(int blocknum, IndirectBlock block) {
		try {
			seek(blocknum);
			for (int i=0; i<block.pointer.length; i++)
				disk.writeInt(block.pointer[i]);
		}
		catch (IOException e) {
			System.err.println(e);
			System.exit(1);
		}
		writeCount++;
	} 
		
	public void stop(boolean removeFile) {
		//System.out.println (toString());
		System.out.println (generateStats());
		if (removeFile)
			fileName.delete();
	}

	public void stop() {
		stop(true);
	}

	/**
	 * Outputs statistics from the file system.
	 */
	//public String toString() {
	public String generateStats() {
		return ("DISK: Read count: " + readCount + " Write count: " + 
			writeCount);
	}
}