/*
* Copyright (c) 2012-2013 TMate Software Ltd
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; version 2 of the License.
*
* This program 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 for more details.
*
* For information on how to redistribute this software under
* the terms of a license other than GNU General Public License
* contact TMate Software at support@hg4j.com
*/
package org.tmatesoft.hg.repo;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.lang.management.ManagementFactory;
import java.net.InetAddress;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;
import org.tmatesoft.hg.core.HgRepositoryLockException;
import org.tmatesoft.hg.internal.Internals;
/**
* <p>Usage:
* <pre>
* HgRepositoryLock lock = hgRepo.getWorkingDirLock();
* try {
* // Actually lock the repo
* lock.acquire();
* ///
* // do whatever modifies working directory
* ...
* } finally {
* if (lock.isLocked()) {
* // this check is needed not to release()
* // erroneously in case acquire() failed (e.g. due to timeout)
* lock.release();
* }
*
* </pre>
*
* Unlike original mechanism, we don't use symlinks, rather files, as it's easier to implement
*
* <p>
* NOT SAFE FOR MULTITHREAD USE!
*
* @see http://code.google.com/p/hg4j/issues/detail?id=35
* @since 1.1
* @author Artem Tikhomirov
* @author TMate Software Ltd.
*/
public class HgRepositoryLock {
/*
* Lock .hg/ except .hg/store/ .hg/wlock (new File(hgRepo.getRepoRoot(),"wlock"))
* Lock .hg/store/ .hg/store/lock (HgRepository.repoPathHelper("lock"))
*/
private final File lockFile;
private int use = 0;
private final int timeoutSeconds;
HgRepositoryLock(File lock, int timeoutInSeconds) {
lockFile = lock;
timeoutSeconds = timeoutInSeconds;
}
/**
* Tries to read lock file and supplies hostname:pid (or just pid) information from there
* @return <code>null</code> if no lock file available at the moment
*/
public String readLockInfo() {
if (lockFile.exists()) {
try {
byte[] bytes = read(lockFile);
if (bytes != null && bytes.length > 0) {
return new String(bytes);
}
} catch (Exception ex) {
// deliberately ignored
}
}
return null;
}
/**
* @return <code>true</code> if we hold the lock
*/
public boolean isLocked() {
return use > 0;
}
/**
* Perform actual locking. Waits for timeout (if specified at construction time)
* before throwing {@link HgRepositoryLockException} in case lock is not available
* immediately.
*
* <p>Multiple calls are possible, but corresponding number of {@link #release()}
* calls shall be made.
* @throws HgRepositoryLockException if failed to grab a lock
*/
public void acquire() throws HgRepositoryLockException {
if (use > 0) {
use++;
return;
}
StringBuilder lockDescription = new StringBuilder();
lockDescription.append(getHostname());
lockDescription.append(':');
lockDescription.append(getPid());
byte[] bytes = lockDescription.toString().getBytes();
long stopTime = timeoutSeconds < 0 ? -1 : (System.currentTimeMillis() + timeoutSeconds*1000);
do {
synchronized(this) {
try {
if (lockFile.createNewFile()) {
write(lockFile, bytes);
use++;
return;
}
} catch (IOException ex) {
// deliberately ignored
}
try {
wait(1000);
} catch (InterruptedException ex) {
// deliberately ignored
}
}
} while (stopTime == -1/*no timeout*/ || System.currentTimeMillis() <= stopTime);
String msg = String.format("Failed to aquire lock, waited for %d seconds, present owner: '%s'", timeoutSeconds, readLockInfo());
throw new HgRepositoryLockException(msg);
}
/**
* Release lock we own
* @throws HgRepositoryLockException if there's no evidence we do own a lock
*/
public void release() throws HgRepositoryLockException {
if (use == 0) {
throw new HgRepositoryLockException("Lock is not held!");
}
use--;
if (use > 0) {
return;
}
// do release
lockFile.delete();
}
protected String getHostname() {
try {
return InetAddress.getLocalHost().getHostName();
} catch (Exception ex) {
return "localhost";
}
}
protected int getPid() {
try {
// @see http://blog.igorminar.com/2007/03/how-java-application-can-discover-its.html
if (!Internals.runningOnWindows()) {
File f = new File("/proc/self");
if (f.exists()) {
// /proc/self is a symlink to /proc/pid/ directory
return Integer.parseInt(f.getCanonicalFile().getName());
}
}
String rtBean = ManagementFactory.getRuntimeMXBean().getName();
int x;
if ((x = rtBean.indexOf('@')) != -1) {
return Integer.parseInt(rtBean.substring(0, x));
}
return -1;
} catch (Exception ex) {
return -1;
}
}
private static void write(File f, byte[] content) throws IOException {
FileOutputStream fos = new FileOutputStream(f);
fos.write(content);
fos.close();
}
private static byte[] read(File f) throws IOException {
FileInputStream fis = new FileInputStream(f);
FileChannel fc = fis.getChannel();
ByteBuffer bb = ByteBuffer.allocate(Internals.ltoi(fc.size()));
fc.read(bb);
fis.close();
return bb.array();
}
}