PortFile.java revision 2593:035b01d356ee 
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 com.sun.tools.javac.util.Assert;
37import com.sun.tools.sjavac.Log;
38
39/**
40 * The PortFile class mediates access to a short binary file containing the tcp/ip port (for the localhost)
41 * and a cookie necessary for the server answering on that port. The file can be locked using file system
42 * primitives to avoid race conditions when several javac clients are started at the same. Note that file
43 * system locking is not always supported on a all operating systems and/or file systems.
44 *
45 *  <p><b>This is NOT part of any supported API.
46 *  If you write code that depends on this, you do so at your own risk.
47 *  This code and its internal interfaces are subject to change or
48 *  deletion without notice.</b>
49 */
50public class PortFile {
51
52    // Port file format:
53    // byte ordering: high byte first = big endian
54    // Magic nr, 4 byte int, first in file.
55    private final static int magicNr = 0x1174;
56    // Followed by a 4 byte int, with the port nr.
57    // Followed by a 8 byte long, with cookie nr.
58
59    private String filename;
60    private File file;
61    private File stopFile;
62    private RandomAccessFile rwfile;
63    private FileChannel channel;
64    private FileLock lock;
65
66    private boolean containsPortInfo;
67    private int serverPort;
68    private long serverCookie;
69    private int myServerPort;
70    private long myServerCookie;
71
72    /**
73     * Create a new portfile.
74     * @param filename is the path to the file.
75     */
76    public PortFile(String fn) throws FileNotFoundException {
77        filename = fn;
78        file = new File(filename);
79        stopFile = new File(filename+".stop");
80        rwfile = new RandomAccessFile(file, "rw");
81        // The rwfile should only be readable by the owner of the process
82        // and no other! How do we do that on a RandomAccessFile?
83        channel = rwfile.getChannel();
84        containsPortInfo = false;
85        lock = null;
86    }
87
88    /**
89     * Lock the port file.
90     */
91    public void lock() throws IOException {
92        lock = channel.lock();
93    }
94
95    /**
96     * Read the values from the port file in the file system.
97     * Expects the port file to be locked.
98     */
99    public void getValues()  {
100        containsPortInfo = false;
101        if (lock == null) {
102            // Not locked, remain ignorant about port file contents.
103            return;
104        }
105        try {
106            if (rwfile.length()>0) {
107                rwfile.seek(0);
108                int nr = rwfile.readInt();
109                serverPort = rwfile.readInt();
110                serverCookie = rwfile.readLong();
111
112                if (nr == magicNr) {
113                    containsPortInfo = true;
114                } else {
115                    containsPortInfo = false;
116                }
117            }
118        } catch (IOException e) {
119            containsPortInfo = false;
120        }
121    }
122
123    /**
124     * Did the locking and getValues succeed?
125     */
126    public boolean containsPortInfo() {
127        return containsPortInfo;
128    }
129
130    /**
131     * If so, then we can acquire the tcp/ip port on localhost.
132     */
133    public int getPort() {
134        Assert.check(containsPortInfo);
135        return serverPort;
136    }
137
138    /**
139     * If so, then we can acquire the server cookie.
140     */
141    public long getCookie() {
142        Assert.check(containsPortInfo);
143        return serverCookie;
144    }
145
146    /**
147     * Store the values into the locked port file.
148     */
149    public void setValues(int port, long cookie) throws IOException {
150        Assert.check(lock != null);
151        rwfile.seek(0);
152        // Write the magic nr that identifes a port file.
153        rwfile.writeInt(magicNr);
154        rwfile.writeInt(port);
155        rwfile.writeLong(cookie);
156        myServerPort = port;
157        myServerCookie = cookie;
158    }
159
160    /**
161     * Delete the port file.
162     */
163    public void delete() throws IOException {
164        // Access to file must be closed before deleting.
165        rwfile.close();
166        // Now delete.
167        file.delete();
168    }
169
170    /**
171     * Is the port file still there?
172     */
173    public boolean exists() throws IOException {
174        return file.exists();
175    }
176
177    /**
178     * Is a stop file there?
179     */
180    public boolean markedForStop() throws IOException {
181        if (stopFile.exists()) {
182            try {
183                stopFile.delete();
184            } catch (Exception e)
185            {}
186            return true;
187        }
188        return false;
189    }
190
191    /**
192     * Unlock the port file.
193     */
194    public void unlock() throws IOException {
195        Assert.check(lock != null);
196        lock.release();
197        lock = null;
198    }
199
200    /**
201     * Wait for the port file to contain values that look valid.
202     * Return true, if a-ok, false if the valid values did not materialize within 5 seconds.
203     */
204    public synchronized boolean waitForValidValues() throws IOException, FileNotFoundException {
205        for (int tries = 0; tries < 50; tries++) {
206            lock();
207            getValues();
208            unlock();
209            if (containsPortInfo) {
210                Log.debug("Found valid values in port file after waiting "+(tries*100)+"ms");
211                return true;
212            }
213            try {
214                Thread.sleep(100);
215            } catch (InterruptedException e)
216            {}
217        }
218        Log.debug("Gave up waiting for valid values in port file");
219        return false;
220    }
221
222    /**
223     * Check if the portfile still contains my values, assuming that I am the server.
224     */
225    public synchronized boolean stillMyValues() throws IOException, FileNotFoundException {
226        for (;;) {
227            try {
228                lock();
229                getValues();
230                unlock();
231                if (containsPortInfo) {
232                    if (serverPort == myServerPort &&
233                        serverCookie == myServerCookie) {
234                        // Everything is ok.
235                        return true;
236                    }
237                    // Someone has overwritten the port file.
238                    // Probably another javac server, lets quit.
239                    return false;
240                }
241                // Something else is wrong with the portfile. Lets quit.
242                return false;
243            } catch (FileLockInterruptionException e) {
244                continue;
245            }
246            catch (ClosedChannelException e) {
247                // The channel has been closed since sjavac is exiting.
248                return false;
249            }
250        }
251    }
252
253    /**
254     * Return the name of the port file.
255     */
256    public String getFilename() {
257        return filename;
258    }
259}
260