Lockfile.java

/*************************GO-LICENSE-START*********************************
 * Copyright 2014 ThoughtWorks, 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.
 *************************GO-LICENSE-END***********************************/

package com.thoughtworks.go.agent.launcher;

import java.io.File;
import java.io.IOException;

import org.apache.commons.io.FileUtils;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public class Lockfile implements Runnable {
    private static final Log LOG = LogFactory.getLog(Lockfile.class);

    static final String TOUCH_FREQUENCY_PROPERTY = "lockfile.touch.frequency.mins";
    static final String SLEEP_TIME_FOR_LAST_MODIFIED_CHECK_PROPERTY = "lockfile.sleep.before.lastmodified.check.secs";

    private static final int DEFAULT_TOUCH_FREQUENCY = 5 * 60 * 1000; // 5 minutes
    private static final int DEFAULT_SLEEP_TIME_FOR_LAST_MODIFIED_CHECK = 10000; // 10 secs

    private final File lockFile;
    private final int touchFrequency;
    private Thread touchLoop;
    private volatile boolean keepRunning;
    private final int sleepTimeBeforeLastModifiedCheck;

    public Lockfile(File filename) {
        this.lockFile = filename;
        this.touchFrequency = getIntProperty(TOUCH_FREQUENCY_PROPERTY, DEFAULT_TOUCH_FREQUENCY);
        this.sleepTimeBeforeLastModifiedCheck = getIntProperty(SLEEP_TIME_FOR_LAST_MODIFIED_CHECK_PROPERTY,
                DEFAULT_SLEEP_TIME_FOR_LAST_MODIFIED_CHECK);
    }

    private int getIntProperty(String propertyName, int defaultValue) {
        int propValue = defaultValue;
        String propValueSet = System.getProperty(propertyName);
        if (propValueSet != null) {
            try {
                propValue = Integer.parseInt(propValueSet);
            } catch (Exception e) {
            }
        }
        return propValue;
    }

    boolean exists() {
        return lockFile.exists() && lockFileChangedWithinMinutes(10);
    }

    boolean lockFileChangedWithinMinutes(int minutes) {
        sleepForSomeTime(); // prevents race condition where the file was just created and not modified.
        long changedAgo = System.currentTimeMillis() - lockFile.lastModified();
        return changedAgo < minutes * 60 * 1000;
    }

    private void sleepForSomeTime() {
        try {
            LOG.info("Sleeping for " + sleepTimeBeforeLastModifiedCheck + " secs to before 'last modified check'...");
            Thread.sleep(sleepTimeBeforeLastModifiedCheck);
        } catch (InterruptedException e) {
        }
    }

    void setHooks() throws IOException {
        touch();
        spawnTouchLoop();
    }

    void touch() throws IOException {
        FileUtils.touch(lockFile);
    }

    synchronized void spawnTouchLoop() {
        if (touchLoop == null) {
            keepRunning = true;
            touchLoop = new Thread(this);
            touchLoop.setName("TouchLoop" + touchLoop.getName());
            touchLoop.setDaemon(true);
            touchLoop.start();
        }
    }

    public String toString() {
        return "<Lockfile: " + lockFile.getAbsolutePath() + ">";
    }

    public void run() {
        LOG.info("Using lock file: " + lockFile.getAbsolutePath());
        do {
            try {
                touch();
                Thread.sleep(touchFrequency);
            } catch (Exception e) {
                return;
            }
        } while (keepRunning);
    }

    public synchronized void delete() {
        requestTouchLoopToStop();
        waitForTouchLoopThread();
        try {
            deleteLockFile();
        } catch (Exception e) {
            LOG.error("Error deleting lock file at " + lockFile.getAbsolutePath(), e);
        }
    }


    private void requestTouchLoopToStop() {
        keepRunning = false;
        if (touchLoop != null) {
            touchLoop.interrupt();
        }
    }

    private void deleteLockFile() {
        if (touchLoop == null) {
            //I haven't got the lock
            return;
        }
        if (!lockFile.exists()) {
            LOG.warn("No lock file found at " + lockFile.getAbsolutePath());
            return;
        }
        if (!lockFile.delete()) {
            LOG.error("Unable to delete lock file at " + lockFile.getAbsolutePath());
        } 
    }

    private void waitForTouchLoopThread() {
        try {
            if (touchLoop != null) {
                // 10 secs for join
                touchLoop.join(10000);
            }
        } catch (InterruptedException e) {
        }
    }

    public boolean tryLock() {
        if (exists()) {
            String alreadyRunningMsg = "Already running agent launcher in this folder.";
            System.out.println(alreadyRunningMsg);
            LOG.error(alreadyRunningMsg);
            return false;
        }

        try {
            setHooks();
            return true;
        } catch (IOException e) {
            String lockFileFailMsg = "Unable to lock file (" + lockFile.getAbsolutePath() + ")";
            System.err.println(lockFileFailMsg);
            LOG.error(lockFileFailMsg, e);
            return false;
        }
    }

}