Glassfish example source code file (ManagedFile.java)

This example Glassfish source code file (ManagedFile.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Glassfish tags/keywords

atomicinteger, file, filelock, filelock, interruptedexception, io, ioexception, ioexception, log, logging, managedfile, managedlock, override, override, randomaccessfile, threading, threads, timeoutexception, timeoutexception, util

The Glassfish ManagedFile.java source code

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 *
 * Copyright (c) 2010 Oracle and/or its affiliates. All rights reserved.
 *
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License.  You can
 * obtain a copy of the License at
 * https://glassfish.dev.java.net/public/CDDL+GPL_1_1.html
 * or packager/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 *
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at packager/legal/LICENSE.txt.
 *
 * GPL Classpath Exception:
 * Oracle designates this particular file as subject to the "Classpath"
 * exception as provided by Oracle in the GPL Version 2 section of the License
 * file that accompanied this code.
 *
 * Modifications:
 * If applicable, add the following below the License Header, with the fields
 * enclosed by brackets [] replaced by your own identifying information:
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 * its licensees as provided above.  However, if you add GPL Version 2 code
 * and therefore, elected the GPL Version 2 license, then the option applies
 * only if the new code is made subject to such option by the copyright
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 */

package org.glassfish.common.util.admin;

import com.sun.enterprise.util.LocalStringManagerImpl;
import com.sun.logging.LogDomains;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.channels.FileChannel;
import java.nio.channels.FileLock;
import java.nio.channels.OverlappingFileLockException;
import java.util.Queue;
import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Defines the notion of a managed file with a classic Read-Write locking policy.
 * A managed file can be locked for multiple concurrent reads or a single write.
 * <p/>
 * A simple example could follow this :
 * <p/>
 * ManagedFile managedFile = new ManagedFile(new File(...), 1000, -1);
 * Lock writeLock;
 * try {
 * writeLock = managedFile.writeAccess();
 * // write or delete the file
 * } finally {
 * writeLock.unlock();
 * }
 *
 * @author Jerome Dochez
 */
public class ManagedFile {

    final File file;
    final int maxHoldingTime;
    final int timeOut;
    final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
    final ManagedFile.RefCounterLock rl = new ManagedFile.RefCounterLock(rwl.readLock(), true);
    final ManagedFile.RefCounterLock wl = new ManagedFile.RefCounterLock(rwl.writeLock(), false);
    final Queue<Thread> waiters = new ConcurrentLinkedQueue();

    final static Logger logger = LogDomains.getLogger(ManagedFile.class, LogDomains.ADMIN_LOGGER);
    final static LocalStringManagerImpl localStrings =
            new LocalStringManagerImpl(ParamTokenizer.class);

    public interface ManagedLock extends java.util.concurrent.locks.Lock {
        public RandomAccessFile getLockedFile();    
    }
    /**
     * Creates a new managed file.
     *
     * @param file           the file to manage
     * @param timeOut        the max time in milliseconds to wait for a read or write lock
     * @param maxHoldingTime the max time in milliseconds to hold the read or write lock
     * @throws IOException when the file cannot be locked
     */
    public ManagedFile(File file, int timeOut, int maxHoldingTime) throws IOException {
        this.file = file;
        this.maxHoldingTime = maxHoldingTime;
        this.timeOut = timeOut;
    }


    /**
     * Blocks for {@link ManagedFile#timeOut} milliseconds for the write access
     * to the managed file.
     *
     * @return the lock instance on the locked file.
     * @throws IOException      if the file cannot be locked
     * @throws TimeoutException if the lock cannot be obtained before the timeOut
     *                          expiration.
     */
    public ManagedLock accessWrite() throws IOException, TimeoutException {
        wl._lock();
        return wl;
    }

    /**
     * Blocks for {@link ManagedFile#timeOut} milliseconds for the read access
     * to the managed file.
     *
     * @return the lock instance on the locked file.
     * @throws IOException      if the file cannot be locked
     * @throws TimeoutException if the lock cannot be obtained before the timeOut
     *                          expiration.
     */
    public ManagedLock accessRead() throws IOException, TimeoutException {
        rl._lock();
        return rl;
    }

    /**
     * Many threads can be requesting the shared read lock, we must keep track
     * through a reference counter when all these users are done. Each thread
     * must call {@link RefCounterLock#unlock()} to release the lock, when the
     * reference counter returns to zero, the file lock is release.
     */
    private class RefCounterLock implements ManagedLock {
        final java.util.concurrent.locks.Lock lock;
        final boolean read;
        final AtomicInteger refs = new AtomicInteger(0);
        FileLock fileLock;
        RandomAccessFile raf;
        FileChannel fc;
        Timer timer;

        public RandomAccessFile getLockedFile() {
            return raf;
        }

        private FileLock get(FileChannel fc, boolean shared) throws IOException, TimeoutException {

            FileLock fl;

            boolean wasInterrupted = false;
            Thread current = Thread.currentThread();
            waiters.add(current);

            // calculate how much time we want to be blocked for
            long endTime = System.currentTimeMillis() + timeOut;
            // so far, we wait in 1/10th increment of the requested timeOut.
            final int individualWaitTime = timeOut / 10;

            // Block while not first in queue or cannot acquire lock
            while (waiters.peek() != current ||
                    (fl = getLock(fc, shared)) == null) {
                // I cannot just park the thread and signal it since the
                // the lock maybe owned by a different process. I just need
                // to wait...

                if (logger.isLoggable(Level.FINE)) {
                    logger.fine("Waiting..." + individualWaitTime);
                }
                if (System.currentTimeMillis() > endTime) {
                    throw new TimeoutException(localStrings.getLocalString("FileLockTimeOut",
                            "time out expired on locking {0}", file.getPath()));
                }
                try {
                    Thread.sleep(individualWaitTime);
                } catch (InterruptedException e) {
                    wasInterrupted = true;
                }
                if (Thread.interrupted()) // ignore interrupts while waiting
                    wasInterrupted = true;
            }

            waiters.remove();
            if (wasInterrupted)          // reassert interrupt status on exit
                current.interrupt();

            return fl;

        }

        private FileLock getLock(FileChannel fc, boolean shared) throws IOException {
            try {
                return fc.lock(0, Long.MAX_VALUE, shared);
            } catch (OverlappingFileLockException e) {
                return null;
            }
        }

        private synchronized FileLock access(boolean shared, String mode, int timeOut) throws IOException, TimeoutException {
            raf = new RandomAccessFile(file, mode);
            fc = raf.getChannel();
            final FileLock fl = get(fc, shared);
            if (maxHoldingTime != -1) {
                timer = new Timer();
                timer.schedule(new TimerTask() {
                    @Override
                    public void run() {
                        try {
                            if (fl.isValid()) {
                                logger.severe(localStrings.getLocalString("FileLockNotReleased",
                                        "File Lock not released on {0}", file.getPath()));
                                release(fl);
                            }
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }, timeOut);
            }
            return fl;
        }

        private synchronized void release(FileLock lock) throws IOException {
            lock.release();
            if (timer != null) {
                timer.cancel();
                timer = null;
            }
            if (raf != null) {
                raf.close();
                raf = null;
            }
            if (fc != null) {
                fc.close();
                fc = null;
            }
        }

        private RefCounterLock(java.util.concurrent.locks.Lock lock, boolean read) {
            this.lock = lock;
            this.read = read;
        }

        public void _lock() throws IOException, TimeoutException {
            lock.lock();
            if (refs.incrementAndGet() == 1) {
                // create the file lock.
                if (read) {
                    fileLock = access(true, "r", maxHoldingTime);
                } else {
                    fileLock = access(false, "rw", maxHoldingTime);
                }
            }
        }

        @Override
        public void lock() {
            throw new UnsupportedOperationException();
        }

        @Override
        public void lockInterruptibly() throws InterruptedException {
            lock.lockInterruptibly();
            refs.incrementAndGet();
        }

        @Override
        public boolean tryLock() {
            boolean result = lock.tryLock();
            if (result) refs.incrementAndGet();
            return result;
        }

        @Override
        public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
            boolean result = lock.tryLock(time, unit);
            if (result) refs.incrementAndGet();
            return result;
        }

        @Override
        public void unlock() {
            lock.unlock();
            if (refs.decrementAndGet() == 0) {
                try {
                    release(fileLock);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

        @Override
        public Condition newCondition() {
            return lock.newCondition();
        }
    }

}