Re: Crash Recovery Schemes

I assume that a basic crash recovery system looks something
like this. It works superficially, although I have not gone crazy
with a debugger. Is there anything obviously stupid about
this scheme, or is it more or less usable?

import java.io.*;

public class CrashRecovery
    implements ITicking, Serializable
{
    // User Constant
    private static final String DEFAULT_FILE_NAME = "recovery.ser";
    private static final String DEFAULT_MIRROR_NAME =
"recovery_mirror.ser";
    private static final int DEFAULT_TIMEOUT = 60 * 60 * 5; //
60fps * 60s/m * 5m

    // System Constant
    private static final int DEFAULT_TICK = 1;
    private static final int ONE_SECOND = 1000; // milliseconds

    // State
    private Serializable mHost;
    private String mFileName;
    private String mMirrorName;
    private int mTimer;
    private int mTimeout;
    private int mVersion;

    public CrashRecovery()
    {
        init(null, DEFAULT_FILE_NAME, DEFAULT_MIRROR_NAME);
    }

    public CrashRecovery(Serializable pHost, String pFileName, String
pMirrorName)
    {
        init(pHost, pFileName, pMirrorName);
    }

    public CrashRecovery init(Serializable pHost, String pFileName,
String pMirrorName)
    {
        setHost(pHost);
        setFile(pFileName, pMirrorName);
        resetTimer();
        resetVersion();
        return this;
    }

    public CrashRecovery setHost(Serializable pHost)
    {
        mHost = pHost;
        return this;
    }

    public CrashRecovery setFile(String pFileName, String pMirrorName)
    {
        mFileName = pFileName;
        mMirrorName = pMirrorName;
        return this;
    }

    // tick every frame
    public void tick()
    {
        tick(DEFAULT_TICK);
    }

    // ITicking supports multiticking
    public void tick(int pTick)
    {
        mTimer += pTick;
        if (mTimeout < mTimer)
        {
            resetTimer();
            save();
        }
    }

    public void setTimeout(int pTimeout)
    {
        mTimeout = pTimeout;
    }

    // because splitting timeout time and FPS is probably a good thing
    public void setTimeout(int pSeconds, int pFps)
    {
        mTimeout = pSeconds * pFps;
    }

    public void resetTimer()
    {
        mTimer = 0;
    }

    private void resetVersion()
    {
        mVersion = 0;
    }

    public boolean save()
    {
        mVersion++;
        resetTimer();
        boolean success = saveState(mFileName);
        success &= saveState(mMirrorName);
        return success;
    }

    public Serializable load()
    {
        Serializable result;
        SerializableShell data = loadShell(mFileName);
        SerializableShell mirror = loadShell(mMirrorName);

        // null is bad
        if ((null == data) && (null == mirror))
        {
            result = null;
        }
        else if (null == data)
        {
            result = mirror.host;
        }
        else if (null == mirror)
        {
            result = data.host;
        }

        // lower version is more reliable
        else if (mirror.version < data.version)
        {
            result = mirror.host;
        }
        else
        {
            result = data.host;
        }
        if (null != result)
        {
            setHost(result);
            resetVersion();
            save();
        }
        return mHost;
    }

    public boolean saveState(String pFilename)
    {
        boolean success;
        try
        {
            SerializableShell data = new SerializableShell(mHost,
mVersion);
            FileOutputStream fos = new
FileOutputStream(pFilename);
            ObjectOutputStream out = new ObjectOutputStream(fos);
            out.writeObject(data);
            out.close();
            success = true;
        }
        catch (IOException e)
        {
            success = false;
        }
        return success;
    }

    public Serializable loadState(String pFilename)
    {
        SerializableShell data = loadShell(pFilename);
        if (null == data)
        {
            return null;
        }
        return data.host;
    }

    private SerializableShell loadShell(String pFilename)
    {
        SerializableShell data = null;
        try
        {
            FileInputStream fis = new
FileInputStream(pFilename);
            ObjectInputStream in = new ObjectInputStream(fis);
            data = (SerializableShell)in.readObject();
            in.close();
        }
        catch (Throwable e)
        {
            data = null;
        }
        return data;
    }

    public boolean deleteFiles()
    {
        boolean success = (new File(mFileName)).delete();
        success &= (new File(mMirrorName)).delete();
        return success;
    }

    class SerializableShell
        implements Serializable
    {
        public Serializable host;
        public int version;

        public SerializableShell(Serializable pHost, int pVersion)
        {
            host = pHost;
            version = pVersion;
        }
    }
}

-Brendan