src/com/android/browser/CrashRecoveryHandler.java

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * 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.
 */

package com.android.browser;

import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.os.Parcel;
import android.util.Log;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class CrashRecoveryHandler {

    private static final String LOGTAG = "BrowserCrashRecovery";
    private static final String STATE_FILE = "browser_state.parcel";
    private static final String RECOVERY_PREFERENCES = "browser_recovery_prefs";
    private static final String KEY_LAST_RECOVERED = "last_recovered";
    private static final int BUFFER_SIZE = 4096;
    private static final long BACKUP_DELAY = 500; // 500ms between writes
    /* This is the duration for which we will prompt to restore
     * instead of automatically restoring. The first time the browser crashes,
     * we will automatically restore. If we then crash again within XX minutes,
     * we will prompt instead of automatically restoring.
     */
    private static final long PROMPT_INTERVAL = 5 * 60 * 1000; // 5 minutes

    private static final int MSG_WRITE_STATE = 1;
    private static final int MSG_CLEAR_STATE = 2;
    private static final int MSG_PRELOAD_STATE = 3;

    private static CrashRecoveryHandler sInstance;

    private Controller mController;
    private Context mContext;
    private Handler mForegroundHandler;
    private Handler mBackgroundHandler;
    private boolean mIsPreloading = false;
    private boolean mDidPreload = false;
    private Bundle mRecoveryState = null;

    public static CrashRecoveryHandler initialize(Controller controller) {
        if (sInstance == null) {
            sInstance = new CrashRecoveryHandler(controller);
        } else {
            sInstance.mController = controller;
        }
        return sInstance;
    }

    public static CrashRecoveryHandler getInstance() {
        return sInstance;
    }

    private CrashRecoveryHandler(Controller controller) {
        mController = controller;
        mContext = mController.getActivity().getApplicationContext();
        mForegroundHandler = new Handler();
        mBackgroundHandler = new Handler(BackgroundHandler.getLooper()) {

            @Override
            public void handleMessage(Message msg) {
                switch (msg.what) {
                case MSG_WRITE_STATE:
                    Parcel p = Parcel.obtain();
                    try {
                        Bundle state = (Bundle) msg.obj;
                        state.writeToParcel(p, 0);
                        File stateFile = new File(mContext.getCacheDir(), STATE_FILE);
                        FileOutputStream fout = new FileOutputStream(stateFile);
                        fout.write(p.marshall());
                        fout.close();
                    } catch (Throwable e) {
                        Log.i(LOGTAG, "Failed to save persistent state", e);
                    } finally {
                        p.recycle();
                    }
                    break;
                case MSG_CLEAR_STATE:
                    File state = new File(mContext.getCacheDir(), STATE_FILE);
                    if (state.exists()) {
                        state.delete();
                    }
                    break;
                case MSG_PRELOAD_STATE:
                    mRecoveryState = loadCrashState();
                    synchronized (CrashRecoveryHandler.this) {
                        mIsPreloading = false;
                        mDidPreload = true;
                        CrashRecoveryHandler.this.notifyAll();
                    }
                    break;
                }
            }
        };
    }

    public void backupState() {
        mForegroundHandler.postDelayed(mCreateState, BACKUP_DELAY);
    }

    private Runnable mCreateState = new Runnable() {

        @Override
        public void run() {
            try {
                final Bundle state = new Bundle();
                mController.onSaveInstanceState(state);
                Message.obtain(mBackgroundHandler, MSG_WRITE_STATE, state)
                        .sendToTarget();
                // Remove any queued up saves
                mForegroundHandler.removeCallbacks(mCreateState);
            } catch (Throwable t) {
                Log.w(LOGTAG, "Failed to save state", t);
                return;
            }
        }

    };

    public void clearState() {
        mBackgroundHandler.sendEmptyMessage(MSG_CLEAR_STATE);
        updateLastRecovered(0);
    }

    private boolean shouldRestore() {
        SharedPreferences prefs = mContext.getSharedPreferences(
                RECOVERY_PREFERENCES, Context.MODE_PRIVATE);
        long lastRecovered = prefs.getLong(KEY_LAST_RECOVERED, 0);
        long timeSinceLastRecover = System.currentTimeMillis() - lastRecovered;
        if (timeSinceLastRecover > PROMPT_INTERVAL) {
            return true;
        }
        return false;
    }

    private void updateLastRecovered(long time) {
        SharedPreferences prefs = mContext.getSharedPreferences(
                RECOVERY_PREFERENCES, Context.MODE_PRIVATE);
        prefs.edit()
            .putLong(KEY_LAST_RECOVERED, time)
            .apply();
    }

    private Bundle loadCrashState() {
        if (!shouldRestore()) {
            return null;
        }
        Bundle state = null;
        Parcel parcel = Parcel.obtain();
        FileInputStream fin = null;
        try {
            File stateFile = new File(mContext.getCacheDir(), STATE_FILE);
            fin = new FileInputStream(stateFile);
            ByteArrayOutputStream dataStream = new ByteArrayOutputStream();
            byte[] buffer = new byte[BUFFER_SIZE];
            int read;
            while ((read = fin.read(buffer)) > 0) {
                dataStream.write(buffer, 0, read);
            }
            byte[] data = dataStream.toByteArray();
            parcel.unmarshall(data, 0, data.length);
            parcel.setDataPosition(0);
            state = parcel.readBundle();
        } catch (FileNotFoundException e) {
            // No state to recover
            state = null;
        } catch (Throwable e) {
            Log.w(LOGTAG, "Failed to recover state!", e);
            state = null;
        } finally {
            parcel.recycle();
            if (fin != null) {
                try {
                    fin.close();
                } catch (IOException e) { }
            }
        }
        if (state != null && !state.isEmpty()) {
            return state;
        }
        return null;
    }

    public void startRecovery(Intent intent) {
        synchronized (CrashRecoveryHandler.this) {
            while (mIsPreloading) {
                try {
                    CrashRecoveryHandler.this.wait();
                } catch (InterruptedException e) {}
            }
        }
        if (!mDidPreload) {
            mRecoveryState = loadCrashState();
        }
        updateLastRecovered(mRecoveryState != null
                ? System.currentTimeMillis() : 0);
        mController.doStart(mRecoveryState, intent);
        mRecoveryState = null;
    }

    public void preloadCrashState() {
        synchronized (CrashRecoveryHandler.this) {
            if (mIsPreloading) {
                return;
            }
            mIsPreloading = true;
        }
        mBackgroundHandler.sendEmptyMessage(MSG_PRELOAD_STATE);
    }

}