diff -r 000000000000 -r 959103a6100f src/share/classes/com/sun/tools/sjavac/server/PortFile.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/classes/com/sun/tools/sjavac/server/PortFile.java	Wed Apr 27 01:34:52 2016 +0800
@@ -0,0 +1,259 @@
+/*
+ * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
+ * 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 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></p>
+ */
+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;
+    private FileLock lock;
+
+    private boolean containsPortInfo;
+    private int serverPort;
+    private long serverCookie;
+    private int myServerPort;
+    private long myServerCookie;
+
+    /**
+     * Create a new portfile.
+     * @param filename is the path to the file.
+     */
+    public PortFile(String fn) throws FileNotFoundException
+    {
+        filename = fn;
+        file = new File(filename);
+        stopFile = new File(filename+".stop");
+        rwfile = new RandomAccessFile(file, "rw");
+        // 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.
+     */
+    void lock() throws IOException {
+        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 (Exception 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(containsPortInfo);
+        return serverPort;
+    }
+
+    /**
+     * If so, then we can acquire the server cookie.
+     */
+    public long getCookie() {
+        assert(containsPortInfo);
+        return serverCookie;
+    }
+
+    /**
+     * Store the values into the locked port file.
+     */
+    public void setValues(int port, long cookie) throws IOException {
+        assert(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(lock != null);
+        lock.release();
+        lock = null;
+    }
+
+    /**
+     * Wait for the port file to contain values that look valid.
+     * Return true, if a-ok, false if the valid values did not materialize within 5 seconds.
+     */
+    public synchronized boolean waitForValidValues() throws IOException, FileNotFoundException {
+        for (int tries = 0; tries < 50; tries++) {
+            lock();
+            getValues();
+            unlock();
+            if (containsPortInfo) {
+                Log.debug("Found valid values in port file after waiting "+(tries*100)+"ms");
+                return true;
+            }
+            try {
+                Thread.sleep(100);
+            } catch (InterruptedException e)
+            {}
+        }
+        Log.debug("Gave up waiting for valid values in port file");
+        return false;
+    }
+
+    /**
+     * Check if the portfile still contains my values, assuming that I am the server.
+     */
+    public synchronized boolean stillMyValues() throws IOException, FileNotFoundException {
+        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;
+    }
+}