1 /*
   2  * Copyright (c) 2008, 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 
  26 package sun.nio.fs;
  27 
  28 import java.nio.file.*;
  29 import java.security.AccessController;
  30 import java.security.PrivilegedAction;
  31 import java.io.IOException;
  32 import java.util.*;
  33 
  34 /**
  35  * Base implementation of background poller thread used in watch service
  36  * implementations. A poller thread waits on events from the file system and
  37  * also services "requests" from clients to register for new events or cancel
  38  * existing registrations.
  39  */
  40 
  41 abstract class AbstractPoller implements Runnable {
  42 
  43     // list of requests pending to the poller thread
  44     private final LinkedList<Request> requestList;
  45 
  46     // set to true when shutdown
  47     private boolean shutdown;
  48 
  49     protected AbstractPoller() {
  50         this.requestList = new LinkedList<>();
  51         this.shutdown = false;
  52     }
  53 
  54     /**
  55      * Starts the poller thread
  56      */
  57     public void start() {
  58         final Runnable thisRunnable = this;
  59         AccessController.doPrivileged(new PrivilegedAction<>() {
  60             @Override
  61             public Object run() {
  62                 Thread thr = new Thread(null, thisRunnable, "FileSystemWatchService", 0, false);
  63                 thr.setDaemon(true);
  64                 thr.start();
  65                 return null;
  66             }
  67          });
  68     }
  69 
  70     /**
  71      * Wakeup poller thread so that it can service pending requests
  72      */
  73     abstract void wakeup() throws IOException;
  74 
  75     /**
  76      * Executed by poller thread to register directory for changes
  77      */
  78     abstract Object implRegister(Path path,
  79                                  Set<? extends WatchEvent.Kind<?>> events,
  80                                  WatchEvent.Modifier... modifiers);
  81 
  82     /**
  83      * Executed by poller thread to cancel key
  84      */
  85     abstract void implCancelKey(WatchKey key);
  86 
  87     /**
  88      * Executed by poller thread to shutdown and cancel all keys
  89      */
  90     abstract void implCloseAll();
  91 
  92     /**
  93      * Requests, and waits on, poller thread to register given file.
  94      */
  95     final WatchKey register(Path dir,
  96                             WatchEvent.Kind<?>[] events,
  97                             WatchEvent.Modifier... modifiers)
  98         throws IOException
  99     {
 100         // validate arguments before request to poller
 101         if (dir == null)
 102             throw new NullPointerException();
 103         Set<WatchEvent.Kind<?>> eventSet = new HashSet<>(events.length);
 104         for (WatchEvent.Kind<?> event: events) {
 105             // standard events
 106             if (event == StandardWatchEventKinds.ENTRY_CREATE ||
 107                 event == StandardWatchEventKinds.ENTRY_MODIFY ||
 108                 event == StandardWatchEventKinds.ENTRY_DELETE)
 109             {
 110                 eventSet.add(event);
 111                 continue;
 112             }
 113 
 114             // OVERFLOW is ignored
 115             if (event == StandardWatchEventKinds.OVERFLOW)
 116                 continue;
 117 
 118             // null/unsupported
 119             if (event == null)
 120                 throw new NullPointerException("An element in event set is 'null'");
 121             throw new UnsupportedOperationException(event.name());
 122         }
 123         if (eventSet.isEmpty())
 124             throw new IllegalArgumentException("No events to register");
 125         return (WatchKey)invoke(RequestType.REGISTER, dir, eventSet, modifiers);
 126     }
 127 
 128     /**
 129      * Cancels, and waits on, poller thread to cancel given key.
 130      */
 131     final void cancel(WatchKey key) {
 132         try {
 133             invoke(RequestType.CANCEL, key);
 134         } catch (IOException x) {
 135             // should not happen
 136             throw new AssertionError(x.getMessage());
 137         }
 138     }
 139 
 140     /**
 141      * Shutdown poller thread
 142      */
 143     final void close() throws IOException {
 144         invoke(RequestType.CLOSE);
 145     }
 146 
 147     /**
 148      * Types of request that the poller thread must handle
 149      */
 150     private static enum RequestType {
 151         REGISTER,
 152         CANCEL,
 153         CLOSE;
 154     }
 155 
 156     /**
 157      * Encapsulates a request (command) to the poller thread.
 158      */
 159     private static class Request {
 160         private final RequestType type;
 161         private final Object[] params;
 162 
 163         private boolean completed = false;
 164         private Object result = null;
 165 
 166         Request(RequestType type, Object... params) {
 167             this.type = type;
 168             this.params = params;
 169         }
 170 
 171         RequestType type() {
 172             return type;
 173         }
 174 
 175         Object[] parameters() {
 176             return params;
 177         }
 178 
 179         void release(Object result) {
 180             synchronized (this) {
 181                 this.completed = true;
 182                 this.result = result;
 183                 notifyAll();
 184             }
 185         }
 186 
 187         /**
 188          * Await completion of the request. The return value is the result of
 189          * the request.
 190          */
 191         Object awaitResult() {
 192             boolean interrupted = false;
 193             synchronized (this) {
 194                 while (!completed) {
 195                     try {
 196                         wait();
 197                     } catch (InterruptedException x) {
 198                         interrupted = true;
 199                     }
 200                 }
 201                 if (interrupted)
 202                     Thread.currentThread().interrupt();
 203                 return result;
 204             }
 205         }
 206     }
 207 
 208     /**
 209      * Enqueues request to poller thread and waits for result
 210      */
 211     private Object invoke(RequestType type, Object... params) throws IOException {
 212         // submit request
 213         Request req = new Request(type, params);
 214         synchronized (requestList) {
 215             if (shutdown) {
 216                 throw new ClosedWatchServiceException();
 217             }
 218             requestList.add(req);
 219         }
 220 
 221         // wakeup thread
 222         wakeup();
 223 
 224         // wait for result
 225         Object result = req.awaitResult();
 226 
 227         if (result instanceof RuntimeException)
 228             throw (RuntimeException)result;
 229         if (result instanceof IOException )
 230             throw (IOException)result;
 231         return result;
 232     }
 233 
 234     /**
 235      * Invoked by poller thread to process all pending requests
 236      *
 237      * @return  true if poller thread should shutdown
 238      */
 239     @SuppressWarnings("unchecked")
 240     boolean processRequests() {
 241         synchronized (requestList) {
 242             Request req;
 243             while ((req = requestList.poll()) != null) {
 244                 // if in process of shutdown then reject request
 245                 if (shutdown) {
 246                     req.release(new ClosedWatchServiceException());
 247                 }
 248 
 249                 switch (req.type()) {
 250                     /**
 251                      * Register directory
 252                      */
 253                     case REGISTER: {
 254                         Object[] params = req.parameters();
 255                         Path path = (Path)params[0];
 256                         Set<? extends WatchEvent.Kind<?>> events =
 257                             (Set<? extends WatchEvent.Kind<?>>)params[1];
 258                         WatchEvent.Modifier[] modifiers =
 259                             (WatchEvent.Modifier[])params[2];
 260                         req.release(implRegister(path, events, modifiers));
 261                         break;
 262                     }
 263                     /**
 264                      * Cancel existing key
 265                      */
 266                     case CANCEL : {
 267                         Object[] params = req.parameters();
 268                         WatchKey key = (WatchKey)params[0];
 269                         implCancelKey(key);
 270                         req.release(null);
 271                         break;
 272                     }
 273                     /**
 274                      * Close watch service
 275                      */
 276                     case CLOSE: {
 277                         implCloseAll();
 278                         req.release(null);
 279                         shutdown = true;
 280                         break;
 281                     }
 282 
 283                     default:
 284                         req.release(new IOException("request not recognized"));
 285                 }
 286             }
 287         }
 288         return shutdown;
 289     }
 290 }