--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/org/tmatesoft/hg/repo/HgRepositoryLock.java	Mon Aug 13 18:11:47 2012 +0200
@@ -0,0 +1,163 @@
+/*
+ * Copyright (c) 2012 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.internal.Internals;
+
+/**
+ * NOT SAFE FOR MULTITHREAD USE!
+ * 
+ * Unlike original mechanism, we don't use symlinks, rather files, as it's easier to implement
+ * 
+ * @author Artem Tikhomirov
+ * @author TMate Software Ltd.
+ */
+public class HgRepositoryLock {
+	/*
+	 * Lock .hg/ except .hg/store/      .hg/wlock (HgRepository.repoPathHelper("wlock"))
+	 * Lock .hg/store/                  .hg/store/lock (HgRepository.repoPathHelper("store/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;
+	}
+	
+	public boolean isLocked() {
+		return use > 0;
+	}
+
+	public void acquire() {
+		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.exists()) {
+						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 HgInvalidStateException(msg);
+	}
+	
+	public void release() {
+		if (use == 0) {
+			throw new HgInvalidStateException("");
+		}
+		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 {
+		FileChannel fc = new FileInputStream(f).getChannel();
+		ByteBuffer bb = ByteBuffer.allocate(Internals.ltoi(fc.size()));
+		fc.read(bb);
+		fc.close();
+		return bb.array();
+	}
+}