PortFile.java revision 2981:d1e5707cd4eb 
1/*
2 * Copyright (c) 2012, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.  Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26package com.sun.tools.sjavac.server;
27
28import java.io.File;
29import java.io.FileNotFoundException;
30import java.io.IOException;
31import java.io.RandomAccessFile;
32import java.nio.channels.ClosedChannelException;
33import java.nio.channels.FileChannel;
34import java.nio.channels.FileLock;
35import java.nio.channels.FileLockInterruptionException;
36import java.util.concurrent.Semaphore;
37
38import com.sun.tools.javac.util.Assert;
39import com.sun.tools.sjavac.Log;
40
41/**
42 * The PortFile class mediates access to a short binary file containing the tcp/ip port (for the localhost)
43 * and a cookie necessary for the server answering on that port. The file can be locked using file system
44 * primitives to avoid race conditions when several javac clients are started at the same. Note that file
45 * system locking is not always supported on a all operating systems and/or file systems.
46 *
47 *  <p><b>This is NOT part of any supported API.
48 *  If you write code that depends on this, you do so at your own risk.
49 *  This code and its internal interfaces are subject to change or
50 *  deletion without notice.</b>
51 */
52public class PortFile {
53
54    // Port file format:
55    // byte ordering: high byte first = big endian
56    // Magic nr, 4 byte int, first in file.
57    private final static int magicNr = 0x1174;
58    // Followed by a 4 byte int, with the port nr.
59    // Followed by a 8 byte long, with cookie nr.
60
61    private String filename;
62    private File file;
63    private File stopFile;
64    private RandomAccessFile rwfile;
65    private FileChannel channel;
66
67    // FileLock used to solve inter JVM synchronization, lockSem used to avoid
68    // JVM internal OverlappingFileLockExceptions.
69    // Class invariant: lock.isValid() <-> lockSem.availablePermits() == 0
70    private FileLock lock;
71    private Semaphore lockSem = new Semaphore(1);
72
73    private boolean containsPortInfo;
74    private int serverPort;
75    private long serverCookie;
76    private int myServerPort;
77    private long myServerCookie;
78
79    /**
80     * Create a new portfile.
81     * @param fn is the path to the file.
82     */
83    public PortFile(String fn) throws FileNotFoundException {
84        filename = fn;
85        file = new File(filename);
86        stopFile = new File(filename+".stop");
87        rwfile = new RandomAccessFile(file, "rw");
88        // The rwfile should only be readable by the owner of the process
89        // and no other! How do we do that on a RandomAccessFile?
90        channel = rwfile.getChannel();
91        containsPortInfo = false;
92        lock = null;
93    }
94
95    /**
96     * Lock the port file.
97     */
98    public void lock() throws IOException, InterruptedException {
99        lockSem.acquire();
100        lock = channel.lock();
101    }
102
103    /**
104     * Read the values from the port file in the file system.
105     * Expects the port file to be locked.
106     */
107    public void getValues()  {
108        containsPortInfo = false;
109        if (lock == null) {
110            // Not locked, remain ignorant about port file contents.
111            return;
112        }
113        try {
114            if (rwfile.length()>0) {
115                rwfile.seek(0);
116                int nr = rwfile.readInt();
117                serverPort = rwfile.readInt();
118                serverCookie = rwfile.readLong();
119
120                if (nr == magicNr) {
121                    containsPortInfo = true;
122                } else {
123                    containsPortInfo = false;
124                }
125            }
126        } catch (IOException e) {
127            containsPortInfo = false;
128        }
129    }
130
131    /**
132     * Did the locking and getValues succeed?
133     */
134    public boolean containsPortInfo() {
135        return containsPortInfo;
136    }
137
138    /**
139     * If so, then we can acquire the tcp/ip port on localhost.
140     */
141    public int getPort() {
142        Assert.check(containsPortInfo);
143        return serverPort;
144    }
145
146    /**
147     * If so, then we can acquire the server cookie.
148     */
149    public long getCookie() {
150        Assert.check(containsPortInfo);
151        return serverCookie;
152    }
153
154    /**
155     * Store the values into the locked port file.
156     */
157    public void setValues(int port, long cookie) throws IOException {
158        Assert.check(lock != null);
159        rwfile.seek(0);
160        // Write the magic nr that identifes a port file.
161        rwfile.writeInt(magicNr);
162        rwfile.writeInt(port);
163        rwfile.writeLong(cookie);
164        myServerPort = port;
165        myServerCookie = cookie;
166    }
167
168    /**
169     * Delete the port file.
170     */
171    public void delete() throws IOException {
172        // Access to file must be closed before deleting.
173        rwfile.close();
174        // Now delete.
175        file.delete();
176    }
177
178    /**
179     * Is the port file still there?
180     */
181    public boolean exists() throws IOException {
182        return file.exists();
183    }
184
185    /**
186     * Is a stop file there?
187     */
188    public boolean markedForStop() throws IOException {
189        if (stopFile.exists()) {
190            try {
191                stopFile.delete();
192            } catch (Exception e)
193            {}
194            return true;
195        }
196        return false;
197    }
198
199    /**
200     * Unlock the port file.
201     */
202    public void unlock() throws IOException {
203        Assert.check(lock != null);
204        lock.release();
205        lock = null;
206        lockSem.release();
207    }
208
209    /**
210     * Wait for the port file to contain values that look valid.
211     */
212    public void waitForValidValues() throws IOException, InterruptedException {
213        final int MAX_ATTEMPTS = 10;
214        final int MS_BETWEEN_ATTEMPTS = 500;
215        long startTime = System.currentTimeMillis();
216        for (int attempt = 0; ; attempt++) {
217            Log.debug("Looking for valid port file values...");
218            lock();
219            getValues();
220            unlock();
221            if (containsPortInfo) {
222                Log.debug("Valid port file values found after " + (System.currentTimeMillis() - startTime) + " ms");
223                return;
224            }
225            if (attempt >= MAX_ATTEMPTS) {
226                throw new IOException("No port file values materialized. Giving up after " +
227                                      (System.currentTimeMillis() - startTime) + " ms");
228            }
229            Thread.sleep(MS_BETWEEN_ATTEMPTS);
230        }
231    }
232
233    /**
234     * Check if the portfile still contains my values, assuming that I am the server.
235     */
236    public boolean stillMyValues() throws IOException, FileNotFoundException, InterruptedException {
237        for (;;) {
238            try {
239                lock();
240                getValues();
241                unlock();
242                if (containsPortInfo) {
243                    if (serverPort == myServerPort &&
244                        serverCookie == myServerCookie) {
245                        // Everything is ok.
246                        return true;
247                    }
248                    // Someone has overwritten the port file.
249                    // Probably another javac server, lets quit.
250                    return false;
251                }
252                // Something else is wrong with the portfile. Lets quit.
253                return false;
254            } catch (FileLockInterruptionException e) {
255                continue;
256            }
257            catch (ClosedChannelException e) {
258                // The channel has been closed since sjavac is exiting.
259                return false;
260            }
261        }
262    }
263
264    /**
265     * Return the name of the port file.
266     */
267    public String getFilename() {
268        return filename;
269    }
270}
271