1 /*
   2  * Copyright (c) 2000, 2013, 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.net.ProtocolFamily;
  30 import java.nio.channels.*;
  31 import java.security.AccessController;
  32 import java.security.PrivilegedAction;
  33 import java.util.Iterator;
  34 import java.util.ServiceLoader;
  35 import java.util.ServiceConfigurationError;
  36 import sun.security.action.GetPropertyAction;
  37 
  38 
  39 /**
  40  * Service-provider class for selectors and selectable channels.
  41  *
  42  * <p> A selector provider is a concrete subclass of this class that has a
  43  * zero-argument constructor and implements the abstract methods specified
  44  * below.  A given invocation of the Java virtual machine maintains a single
  45  * system-wide default provider instance, which is returned by the {@link
  46  * #provider() provider} method.  The first invocation of that method will locate
  47  * the default provider as specified below.
  48  *
  49  * <p> The system-wide default provider is used by the static {@code open}
  50  * methods of the {@link java.nio.channels.DatagramChannel#open
  51  * DatagramChannel}, {@link java.nio.channels.Pipe#open Pipe}, {@link
  52  * java.nio.channels.Selector#open Selector}, {@link
  53  * java.nio.channels.ServerSocketChannel#open ServerSocketChannel}, and {@link
  54  * java.nio.channels.SocketChannel#open SocketChannel} classes.  It is also
  55  * used by the {@link java.lang.System#inheritedChannel System.inheritedChannel()}
  56  * method. A program may make use of a provider other than the default provider
  57  * by instantiating that provider and then directly invoking the {@code open}
  58  * methods defined in this class.
  59  *
  60  * <p> All of the methods in this class are safe for use by multiple concurrent
  61  * threads.  </p>
  62  *
  63  *
  64  * @author Mark Reinhold
  65  * @author JSR-51 Expert Group
  66  * @since 1.4
  67  */
  68 
  69 public abstract class SelectorProvider {
  70 
  71     private static final Object lock = new Object();
  72     private static SelectorProvider provider = null;
  73 
  74     private static Void checkPermission() {
  75         SecurityManager sm = System.getSecurityManager();
  76         if (sm != null)
  77             sm.checkPermission(new RuntimePermission("selectorProvider"));
  78         return null;
  79     }
  80     private SelectorProvider(Void ignore) { }
  81 
  82     /**
  83      * Initializes a new instance of this class.
  84      *
  85      * @throws  SecurityException
  86      *          If a security manager has been installed and it denies
  87      *          {@link RuntimePermission}{@code ("selectorProvider")}
  88      */
  89     protected SelectorProvider() {
  90         this(checkPermission());
  91     }
  92 
  93     private static boolean loadProviderFromProperty() {
  94         String cn = System.getProperty("java.nio.channels.spi.SelectorProvider");
  95         if (cn == null)
  96             return false;
  97         try {
  98             @SuppressWarnings("deprecation")
  99             Object tmp = Class.forName(cn, true,
 100                                        ClassLoader.getSystemClassLoader()).newInstance();
 101             provider = (SelectorProvider)tmp;
 102             return true;
 103         } catch (ClassNotFoundException x) {
 104             throw new ServiceConfigurationError(null, x);
 105         } catch (IllegalAccessException x) {
 106             throw new ServiceConfigurationError(null, x);
 107         } catch (InstantiationException x) {
 108             throw new ServiceConfigurationError(null, x);
 109         } catch (SecurityException x) {
 110             throw new ServiceConfigurationError(null, x);
 111         }
 112     }
 113 
 114     private static boolean loadProviderAsService() {
 115 
 116         ServiceLoader<SelectorProvider> sl =
 117             ServiceLoader.load(SelectorProvider.class,
 118                                ClassLoader.getSystemClassLoader());
 119         Iterator<SelectorProvider> i = sl.iterator();
 120         for (;;) {
 121             try {
 122                 if (!i.hasNext())
 123                     return false;
 124                 provider = i.next();
 125                 return true;
 126             } catch (ServiceConfigurationError sce) {
 127                 if (sce.getCause() instanceof SecurityException) {
 128                     // Ignore the security exception, try the next provider
 129                     continue;
 130                 }
 131                 throw sce;
 132             }
 133         }
 134     }
 135 
 136     /**
 137      * Returns the system-wide default selector provider for this invocation of
 138      * the Java virtual machine.
 139      *
 140      * <p> The first invocation of this method locates the default provider
 141      * object as follows: </p>
 142      *
 143      * <ol>
 144      *
 145      *   <li><p> If the system property
 146      *   {@code java.nio.channels.spi.SelectorProvider} is defined then it is
 147      *   taken to be the fully-qualified name of a concrete provider class.
 148      *   The class is loaded and instantiated; if this process fails then an
 149      *   unspecified error is thrown.  </p></li>
 150      *
 151      *   <li><p> If a provider class has been installed in a jar file that is
 152      *   visible to the system class loader, and that jar file contains a
 153      *   provider-configuration file named
 154      *   {@code java.nio.channels.spi.SelectorProvider} in the resource
 155      *   directory {@code META-INF/services}, then the first class name
 156      *   specified in that file is taken.  The class is loaded and
 157      *   instantiated; if this process fails then an unspecified error is
 158      *   thrown.  </p></li>
 159      *
 160      *   <li><p> Finally, if no provider has been specified by any of the above
 161      *   means then the system-default provider class is instantiated and the
 162      *   result is returned.  </p></li>
 163      *
 164      * </ol>
 165      *
 166      * <p> Subsequent invocations of this method return the provider that was
 167      * returned by the first invocation.  </p>
 168      *
 169      * @return  The system-wide default selector provider
 170      */
 171     public static SelectorProvider provider() {
 172         synchronized (lock) {
 173             if (provider != null)
 174                 return provider;
 175             return AccessController.doPrivileged(
 176                 new PrivilegedAction<>() {
 177                     public SelectorProvider run() {
 178                             if (loadProviderFromProperty())
 179                                 return provider;
 180                             if (loadProviderAsService())
 181                                 return provider;
 182                             provider = sun.nio.ch.DefaultSelectorProvider.create();
 183                             return provider;
 184                         }
 185                     });
 186         }
 187     }
 188 
 189     /**
 190      * Opens a datagram channel.
 191      *
 192      * @return  The new channel
 193      *
 194      * @throws  IOException
 195      *          If an I/O error occurs
 196      */
 197     public abstract DatagramChannel openDatagramChannel()
 198         throws IOException;
 199 
 200     /**
 201      * Opens a datagram channel.
 202      *
 203      * @param   family
 204      *          The protocol family
 205      *
 206      * @return  A new datagram channel
 207      *
 208      * @throws  UnsupportedOperationException
 209      *          If the specified protocol family is not supported
 210      * @throws  IOException
 211      *          If an I/O error occurs
 212      *
 213      * @since 1.7
 214      */
 215     public abstract DatagramChannel openDatagramChannel(ProtocolFamily family)
 216         throws IOException;
 217 
 218     /**
 219      * Opens a pipe.
 220      *
 221      * @return  The new pipe
 222      *
 223      * @throws  IOException
 224      *          If an I/O error occurs
 225      */
 226     public abstract Pipe openPipe()
 227         throws IOException;
 228 
 229     /**
 230      * Opens a selector.
 231      *
 232      * @return  The new selector
 233      *
 234      * @throws  IOException
 235      *          If an I/O error occurs
 236      */
 237     public abstract AbstractSelector openSelector()
 238         throws IOException;
 239 
 240     /**
 241      * Opens a server-socket channel.
 242      *
 243      * @return  The new channel
 244      *
 245      * @throws  IOException
 246      *          If an I/O error occurs
 247      */
 248     public abstract ServerSocketChannel openServerSocketChannel()
 249         throws IOException;
 250 
 251     /**
 252      * Opens a socket channel.
 253      *
 254      * @return  The new channel
 255      *
 256      * @throws  IOException
 257      *          If an I/O error occurs
 258      */
 259     public abstract SocketChannel openSocketChannel()
 260         throws IOException;
 261 
 262     /**
 263      * Returns the channel inherited from the entity that created this
 264      * Java virtual machine.
 265      *
 266      * <p> On many operating systems a process, such as a Java virtual
 267      * machine, can be started in a manner that allows the process to
 268      * inherit a channel from the entity that created the process. The
 269      * manner in which this is done is system dependent, as are the
 270      * possible entities to which the channel may be connected. For example,
 271      * on UNIX systems, the Internet services daemon (<i>inetd</i>) is used to
 272      * start programs to service requests when a request arrives on an
 273      * associated network port. In this example, the process that is started,
 274      * inherits a channel representing a network socket.
 275      *
 276      * <p> In cases where the inherited channel represents a network socket
 277      * then the {@link java.nio.channels.Channel Channel} type returned
 278      * by this method is determined as follows:
 279      *
 280      * <ul>
 281      *
 282      *  <li><p> If the inherited channel represents a stream-oriented connected
 283      *  socket then a {@link java.nio.channels.SocketChannel SocketChannel} is
 284      *  returned. The socket channel is, at least initially, in blocking
 285      *  mode, bound to a socket address, and connected to a peer.
 286      *  </p></li>
 287      *
 288      *  <li><p> If the inherited channel represents a stream-oriented listening
 289      *  socket then a {@link java.nio.channels.ServerSocketChannel
 290      *  ServerSocketChannel} is returned. The server-socket channel is, at
 291      *  least initially, in blocking mode, and bound to a socket address.
 292      *  </p></li>
 293      *
 294      *  <li><p> If the inherited channel is a datagram-oriented socket
 295      *  then a {@link java.nio.channels.DatagramChannel DatagramChannel} is
 296      *  returned. The datagram channel is, at least initially, in blocking
 297      *  mode, and bound to a socket address.
 298      *  </p></li>
 299      *
 300      * </ul>
 301      *
 302      * <p> In addition to the network-oriented channels described, this method
 303      * may return other kinds of channels in the future.
 304      *
 305      * <p> The first invocation of this method creates the channel that is
 306      * returned. Subsequent invocations of this method return the same
 307      * channel. </p>
 308      *
 309      * @return  The inherited channel, if any, otherwise {@code null}.
 310      *
 311      * @throws  IOException
 312      *          If an I/O error occurs
 313      *
 314      * @throws  SecurityException
 315      *          If a security manager has been installed and it denies
 316      *          {@link RuntimePermission}{@code ("inheritedChannel")}
 317      *
 318      * @since 1.5
 319      */
 320    public Channel inheritedChannel() throws IOException {
 321         return null;
 322    }
 323 
 324 }