/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package com.sun.tools.sjavac.server;

import java.io.File;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.io.RandomAccessFile;

import java.nio.channels.ClosedChannelException;

import java.nio.channels.FileChannel;

import java.nio.channels.FileLock;

import java.nio.channels.FileLockInterruptionException;

import java.util.concurrent.Semaphore;

import com.sun.tools.javac.util.Assert;

import com.sun.tools.sjavac.Log;

/**

 * The PortFile class mediates access to a short binary file containing the tcp/ip port (for the localhost)

 * and a cookie necessary for the server answering on that port. The file can be locked using file system

 * primitives to avoid race conditions when several javac clients are started at the same. Note that file

 * system locking is not always supported on a all operating systems and/or file systems.

 *

 *  <p><b>This is NOT part of any supported API.

 *  If you write code that depends on this, you do so at your own risk.

 *  This code and its internal interfaces are subject to change or

 *  deletion without notice.</b>

 */

public class PortFile {

    // Port file format:

    // byte ordering: high byte first = big endian

    // Magic nr, 4 byte int, first in file.

    private final static int magicNr = 0x1174;

    // Followed by a 4 byte int, with the port nr.

    // Followed by a 8 byte long, with cookie nr.

    private String filename;

    private File file;

    private File stopFile;

    private RandomAccessFile rwfile;

    private FileChannel channel;

    // FileLock used to solve inter JVM synchronization, lockSem used to avoid

    // JVM internal OverlappingFileLockExceptions.

    // Class invariant: lock.isValid() <-> lockSem.availablePermits() == 0

    private FileLock lock;

    private Semaphore lockSem = new Semaphore(1);

    private boolean containsPortInfo;

    private int serverPort;

    private long serverCookie;

    private int myServerPort;

    private long myServerCookie;

    /**

     * Create a new portfile.

     * @param fn is the path to the file.

     */

        filename = fn;

        file = new File(filename);

        stopFile = new File(filename+".stop");

        // The rwfile should only be readable by the owner of the process

        // and no other! How do we do that on a RandomAccessFile?

        channel = rwfile.getChannel();

        containsPortInfo = false;

        lock = null;

    }

    /**

     * Lock the port file.

     */

    public void lock() throws IOException, InterruptedException {

        lockSem.acquire();

        lock = channel.lock();

    }

    /**

     * Read the values from the port file in the file system.

     * Expects the port file to be locked.

     */

    public void getValues()  {

        containsPortInfo = false;

        if (lock == null) {

            // Not locked, remain ignorant about port file contents.

            return;

        }

        try {

            if (rwfile.length()>0) {

                rwfile.seek(0);

                int nr = rwfile.readInt();

                serverPort = rwfile.readInt();

                serverCookie = rwfile.readLong();

                if (nr == magicNr) {

                    containsPortInfo = true;

                } else {

                    containsPortInfo = false;

                }

            }

        } catch (IOException e) {

            containsPortInfo = false;

        }

    }

    /**

     * Did the locking and getValues succeed?

     */

    public boolean containsPortInfo() {

        return containsPortInfo;

    }

    /**

     * If so, then we can acquire the tcp/ip port on localhost.

     */

    public int getPort() {

        Assert.check(containsPortInfo);

        return serverPort;

    }

    /**

     * If so, then we can acquire the server cookie.

     */

    public long getCookie() {

        Assert.check(containsPortInfo);

        return serverCookie;

    }

    /**

     * Store the values into the locked port file.

     */

    public void setValues(int port, long cookie) throws IOException {

        Assert.check(lock != null);

        rwfile.seek(0);

        // Write the magic nr that identifes a port file.

        rwfile.writeInt(magicNr);

        rwfile.writeInt(port);

        rwfile.writeLong(cookie);

        myServerPort = port;

        myServerCookie = cookie;

    }

    /**

     * Delete the port file.

     */

    public void delete() throws IOException {

        // Access to file must be closed before deleting.

        rwfile.close();

        // Now delete.

        file.delete();

    }

    /**

     * Is the port file still there?

     */

    public boolean exists() throws IOException {

        return file.exists();

    }

    /**

     * Is a stop file there?

     */

    public boolean markedForStop() throws IOException {

        if (stopFile.exists()) {

            try {

                stopFile.delete();

            } catch (Exception e)

            {}

            return true;

        }

        return false;

    }

    /**

     * Unlock the port file.

     */

    public void unlock() throws IOException {

        Assert.check(lock != null);

        lock.release();

        lock = null;

        lockSem.release();

    }

    /**

     * Wait for the port file to contain values that look valid.

     */

    public void waitForValidValues() throws IOException, InterruptedException {

        final int MAX_ATTEMPTS = 10;

        final int MS_BETWEEN_ATTEMPTS = 500;

        long startTime = System.currentTimeMillis();

        for (int attempt = 0; ; attempt++) {

            Log.debug("Looking for valid port file values...");

            lock();

            getValues();

            unlock();

            if (containsPortInfo) {

                Log.debug("Valid port file values found after " + (System.currentTimeMillis() - startTime) + " ms");

                return;

            }

            if (attempt >= MAX_ATTEMPTS) {

                throw new IOException("No port file values materialized. Giving up after " +

                                      (System.currentTimeMillis() - startTime) + " ms");

            }

            Thread.sleep(MS_BETWEEN_ATTEMPTS);

        }

    }

    /**

     * Check if the portfile still contains my values, assuming that I am the server.

     */

    public boolean stillMyValues() throws IOException, FileNotFoundException, InterruptedException {

        for (;;) {

            try {

                lock();

                getValues();

                unlock();

                if (containsPortInfo) {

                    if (serverPort == myServerPort &&

                        serverCookie == myServerCookie) {

                        // Everything is ok.

                        return true;

                    }

                    // Someone has overwritten the port file.

                    // Probably another javac server, lets quit.

                    return false;

                }

                // Something else is wrong with the portfile. Lets quit.

                return false;

            } catch (FileLockInterruptionException e) {

                continue;

            }

            catch (ClosedChannelException e) {

                // The channel has been closed since sjavac is exiting.

                return false;

            }

        }

    }

    /**

     * Return the name of the port file.

     */

    public String getFilename() {

        return filename;

    }

}