1 /*
   2  * Copyright (c) 2000, 2019, 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 java.nio.channels.spi;
  27 
  28 import java.io.IOException;
  29 import java.lang.reflect.InvocationTargetException;
  30 import java.net.ProtocolFamily;
  31 import java.nio.channels.Channel;
  32 import java.nio.channels.DatagramChannel;
  33 import java.nio.channels.Pipe;
  34 import java.nio.channels.ServerSocketChannel;
  35 import java.nio.channels.SocketChannel;
  36 import java.security.AccessController;
  37 import java.security.PrivilegedAction;
  38 import java.util.Iterator;
  39 import java.util.Objects;
  40 import java.util.ServiceLoader;
  41 import java.util.ServiceConfigurationError;
  42 
  43 /**
  44  * Service-provider class for selectors and selectable channels.
  45  *
  46  * <p> A selector provider is a concrete subclass of this class that has a
  47  * zero-argument constructor and implements the abstract methods specified
  48  * below.  A given invocation of the Java virtual machine maintains a single
  49  * system-wide default provider instance, which is returned by the {@link
  50  * #provider() provider} method.  The first invocation of that method will locate
  51  * the default provider as specified below.
  52  *
  53  * <p> The system-wide default provider is used by the static {@code open}
  54  * methods of the {@link java.nio.channels.DatagramChannel#open
  55  * DatagramChannel}, {@link java.nio.channels.Pipe#open Pipe}, {@link
  56  * java.nio.channels.Selector#open Selector}, {@link
  57  * java.nio.channels.ServerSocketChannel#open ServerSocketChannel}, and {@link
  58  * java.nio.channels.SocketChannel#open SocketChannel} classes.  It is also
  59  * used by the {@link java.lang.System#inheritedChannel System.inheritedChannel()}
  60  * method. A program may make use of a provider other than the default provider
  61  * by instantiating that provider and then directly invoking the {@code open}
  62  * methods defined in this class.
  63  *
  64  * <p> All of the methods in this class are safe for use by multiple concurrent
  65  * threads.  </p>
  66  *
  67  *
  68  * @author Mark Reinhold
  69  * @author JSR-51 Expert Group
  70  * @since 1.4
  71  */
  72 
  73 public abstract class SelectorProvider {
  74 
  75     private static Void checkPermission() {
  76         SecurityManager sm = System.getSecurityManager();
  77         if (sm != null)
  78             sm.checkPermission(new RuntimePermission("selectorProvider"));
  79         return null;
  80     }
  81     private SelectorProvider(Void ignore) { }
  82 
  83     /**
  84      * Initializes a new instance of this class.
  85      *
  86      * @throws  SecurityException
  87      *          If a security manager has been installed and it denies
  88      *          {@link RuntimePermission}{@code ("selectorProvider")}
  89      */
  90     protected SelectorProvider() {
  91         this(checkPermission());
  92     }
  93 
  94     private static class Holder {
  95         static final SelectorProvider INSTANCE = provider();
  96 
  97         static SelectorProvider provider() {
  98             PrivilegedAction<SelectorProvider> pa = () -> {
  99                 SelectorProvider sp;
 100                 if ((sp = loadProviderFromProperty()) != null)
 101                     return sp;
 102                 if ((sp = loadProviderAsService()) != null)
 103                     return sp;
 104                 return sun.nio.ch.DefaultSelectorProvider.get();
 105             };
 106             return AccessController.doPrivileged(pa);
 107         }
 108 
 109         private static SelectorProvider loadProviderFromProperty() {
 110             String cn = System.getProperty("java.nio.channels.spi.SelectorProvider");
 111             if (cn == null)
 112                 return null;
 113             try {
 114                 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
 115                 return (SelectorProvider) clazz.getConstructor().newInstance();
 116             } catch (ClassNotFoundException |
 117                     NoSuchMethodException |
 118                     IllegalAccessException |
 119                     InvocationTargetException |
 120                     InstantiationException |
 121                     SecurityException x) {
 122                 throw new ServiceConfigurationError(null, x);
 123             }
 124         }
 125 
 126         private static SelectorProvider loadProviderAsService() {
 127             ServiceLoader<SelectorProvider> sl =
 128                 ServiceLoader.load(SelectorProvider.class,
 129                                    ClassLoader.getSystemClassLoader());
 130             Iterator<SelectorProvider> i = sl.iterator();
 131             for (;;) {
 132                 try {
 133                     return i.hasNext() ? i.next() : null;
 134                 } catch (ServiceConfigurationError sce) {
 135                     if (sce.getCause() instanceof SecurityException) {
 136                         // Ignore the security exception, try the next provider
 137                         continue;
 138                     }
 139                     throw sce;
 140                 }
 141             }
 142         }
 143     }
 144 
 145     /**
 146      * Returns the system-wide default selector provider for this invocation of
 147      * the Java virtual machine.
 148      *
 149      * <p> The first invocation of this method locates the default provider
 150      * object as follows: </p>
 151      *
 152      * <ol>
 153      *
 154      *   <li><p> If the system property
 155      *   {@systemProperty java.nio.channels.spi.SelectorProvider} is defined
 156      *   then it is taken to be the fully-qualified name of a concrete provider
 157      *   class. The class is loaded and instantiated; if this process fails then
 158      *   an unspecified error is thrown.  </p></li>
 159      *
 160      *   <li><p> If a provider class has been installed in a jar file that is
 161      *   visible to the system class loader, and that jar file contains a
 162      *   provider-configuration file named
 163      *   {@code java.nio.channels.spi.SelectorProvider} in the resource
 164      *   directory {@code META-INF/services}, then the first class name
 165      *   specified in that file is taken.  The class is loaded and
 166      *   instantiated; if this process fails then an unspecified error is
 167      *   thrown.  </p></li>
 168      *
 169      *   <li><p> Finally, if no provider has been specified by any of the above
 170      *   means then the system-default provider class is instantiated and the
 171      *   result is returned.  </p></li>
 172      *
 173      * </ol>
 174      *
 175      * <p> Subsequent invocations of this method return the provider that was
 176      * returned by the first invocation.  </p>
 177      *
 178      * @return  The system-wide default selector provider
 179      */
 180     public static SelectorProvider provider() {
 181         return Holder.INSTANCE;
 182     }
 183 
 184     /**
 185      * Opens a datagram channel.
 186      *
 187      * @return  The new channel
 188      *
 189      * @throws  IOException
 190      *          If an I/O error occurs
 191      */
 192     public abstract DatagramChannel openDatagramChannel()
 193         throws IOException;
 194 
 195     /**
 196      * Opens a datagram channel.
 197      *
 198      * @param   family
 199      *          The protocol family
 200      *
 201      * @return  A new datagram channel
 202      *
 203      * @throws  UnsupportedOperationException
 204      *          If the specified protocol family is not supported
 205      * @throws  IOException
 206      *          If an I/O error occurs
 207      *
 208      * @since 1.7
 209      */
 210     public abstract DatagramChannel openDatagramChannel(ProtocolFamily family)
 211         throws IOException;
 212 
 213     /**
 214      * Opens a pipe.
 215      *
 216      * @return  The new pipe
 217      *
 218      * @throws  IOException
 219      *          If an I/O error occurs
 220      */
 221     public abstract Pipe openPipe()
 222         throws IOException;
 223 
 224     /**
 225      * Opens a selector.
 226      *
 227      * @return  The new selector
 228      *
 229      * @throws  IOException
 230      *          If an I/O error occurs
 231      */
 232     public abstract AbstractSelector openSelector()
 233         throws IOException;
 234 
 235     /**
 236      * Opens a server-socket channel.
 237      *
 238      * @return  The new channel
 239      *
 240      * @throws  IOException
 241      *          If an I/O error occurs
 242      */
 243     public abstract ServerSocketChannel openServerSocketChannel()
 244         throws IOException;
 245 
 246     /**
 247      * Opens a socket channel.
 248      *
 249      * @return  The new channel
 250      *
 251      * @throws  IOException
 252      *          If an I/O error occurs
 253      */
 254     public abstract SocketChannel openSocketChannel()
 255         throws IOException;
 256 
 257     /**
 258      * Returns the channel inherited from the entity that created this
 259      * Java virtual machine.
 260      *
 261      * <p> On many operating systems a process, such as a Java virtual
 262      * machine, can be started in a manner that allows the process to
 263      * inherit a channel from the entity that created the process. The
 264      * manner in which this is done is system dependent, as are the
 265      * possible entities to which the channel may be connected. For example,
 266      * on UNIX systems, the Internet services daemon (<i>inetd</i>) is used to
 267      * start programs to service requests when a request arrives on an
 268      * associated network port. In this example, the process that is started,
 269      * inherits a channel representing a network socket.
 270      *
 271      * <p> In cases where the inherited channel is for an <i>Internet protocol</i>
 272      * socket then the {@link Channel Channel} type returned
 273      * by this method is determined as follows:
 274      *
 275      * <ul>
 276      *
 277      *  <li><p> If the inherited channel is for a stream-oriented connected
 278      *  socket then a {@link SocketChannel SocketChannel} is returned. The
 279      *  socket channel is, at least initially, in blocking mode, bound
 280      *  to a socket address, and connected to a peer.
 281      *  </p></li>
 282      *
 283      *  <li><p> If the inherited channel is for a stream-oriented listening
 284      *  socket then a {@link ServerSocketChannel ServerSocketChannel} is returned.
 285      *  The server-socket channel is, at least initially, in blocking mode,
 286      *  and bound to a socket address.
 287      *  </p></li>
 288      *
 289      *  <li><p> If the inherited channel is a datagram-oriented socket then a
 290      *  {@link DatagramChannel DatagramChannel} is returned. The datagram channel
 291      *  is, at least initially, in blocking mode, and bound to a socket address.
 292      *  </p></li>
 293      *
 294      * </ul>
 295      *
 296      * <p> In cases where the inherited channel is for a <i>Unix domain</i>
 297      * socket then the {@link Channel} type returned is the same as for
 298      * <i>Internet protocol</i> sockets as described above, except that
 299      * datagram-oriented sockets are not supported.
 300      *
 301      * <p> In addition to the two types of socket just described, this method
 302      * may return other types in the future.
 303      *
 304      * <p> The first invocation of this method creates the channel that is
 305      * returned. Subsequent invocations of this method return the same
 306      * channel. </p>
 307      *
 308      * @return  The inherited channel, if any, otherwise {@code null}.
 309      *
 310      * @throws  IOException
 311      *          If an I/O error occurs
 312      *
 313      * @throws  SecurityException
 314      *          If a security manager has been installed and it denies
 315      *          {@link RuntimePermission}{@code ("inheritedChannel")}
 316      *
 317      * @since 1.5
 318      */
 319     public Channel inheritedChannel() throws IOException {
 320         return null;
 321     }
 322 
 323     /**
 324      * Opens a socket channel.
 325      *
 326      * @implSpec The default implementation of this method first checks that
 327      * the given protocol {@code family} is not {@code null},
 328      * then throws {@link UnsupportedOperationException}.
 329      *
 330      * @param   family
 331      *          The protocol family
 332      *
 333      * @return  The new channel
 334      *
 335      * @throws  UnsupportedOperationException
 336      *          If the specified protocol family is not supported
 337      * @throws  IOException
 338      *          If an I/O error occurs
 339      *
 340      * @since 15
 341      */
 342     public SocketChannel openSocketChannel(ProtocolFamily family) throws IOException {
 343         Objects.requireNonNull(family);
 344         throw new UnsupportedOperationException("Protocol family not supported");
 345     }
 346 
 347     /**
 348      * Opens a server-socket channel.
 349      *
 350      * @implSpec The default implementation of this method first checks that
 351      * the given protocol {@code family} is not {@code null},
 352      * then throws {@link UnsupportedOperationException}.
 353      *
 354      * @param   family
 355      *          The protocol family
 356      *
 357      * @return  The new channel
 358      *
 359      * @throws  UnsupportedOperationException
 360      *          If the specified protocol family is not supported
 361      * @throws  IOException
 362      *          If an I/O error occurs
 363      *
 364      * @since 15
 365      */
 366     public ServerSocketChannel openServerSocketChannel(ProtocolFamily family) throws IOException {
 367         Objects.requireNonNull(family);
 368         throw new UnsupportedOperationException("Protocol family not supported");
 369     }
 370 }