1/*
2 * Copyright (c) 2000, 2009, 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
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23 * questions.
24 */
25
26package java.nio.channels.spi;
27
28import java.io.IOException;
29import java.net.ProtocolFamily;
30import java.nio.channels.*;
31import java.security.AccessController;
32import java.security.PrivilegedAction;
33import java.util.Iterator;
34import java.util.ServiceLoader;
35import java.util.ServiceConfigurationError;
36import 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 <tt>open</tt>
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 <tt>open</tt>
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
69public abstract class SelectorProvider {
70
71    private static final Object lock = new Object();
72    private static SelectorProvider provider = null;
73
74    /**
75     * Initializes a new instance of this class.  </p>
76     *
77     * @throws  SecurityException
78     *          If a security manager has been installed and it denies
79     *          {@link RuntimePermission}<tt>("selectorProvider")</tt>
80     */
81    protected SelectorProvider() {
82        SecurityManager sm = System.getSecurityManager();
83        if (sm != null)
84            sm.checkPermission(new RuntimePermission("selectorProvider"));
85    }
86
87    private static boolean loadProviderFromProperty() {
88        String cn = System.getProperty("java.nio.channels.spi.SelectorProvider");
89        if (cn == null)
90            return false;
91        try {
92            Class<?> c = Class.forName(cn, true,
93                                       ClassLoader.getSystemClassLoader());
94            provider = (SelectorProvider)c.newInstance();
95            return true;
96        } catch (ClassNotFoundException x) {
97            throw new ServiceConfigurationError(null, x);
98        } catch (IllegalAccessException x) {
99            throw new ServiceConfigurationError(null, x);
100        } catch (InstantiationException x) {
101            throw new ServiceConfigurationError(null, x);
102        } catch (SecurityException x) {
103            throw new ServiceConfigurationError(null, x);
104        }
105    }
106
107    private static boolean loadProviderAsService() {
108
109        ServiceLoader<SelectorProvider> sl =
110            ServiceLoader.load(SelectorProvider.class,
111                               ClassLoader.getSystemClassLoader());
112        Iterator<SelectorProvider> i = sl.iterator();
113        for (;;) {
114            try {
115                if (!i.hasNext())
116                    return false;
117                provider = i.next();
118                return true;
119            } catch (ServiceConfigurationError sce) {
120                if (sce.getCause() instanceof SecurityException) {
121                    // Ignore the security exception, try the next provider
122                    continue;
123                }
124                throw sce;
125            }
126        }
127    }
128
129    /**
130     * Returns the system-wide default selector provider for this invocation of
131     * the Java virtual machine.
132     *
133     * <p> The first invocation of this method locates the default provider
134     * object as follows: </p>
135     *
136     * <ol>
137     *
138     *   <li><p> If the system property
139     *   <tt>java.nio.channels.spi.SelectorProvider</tt> is defined then it is
140     *   taken to be the fully-qualified name of a concrete provider class.
141     *   The class is loaded and instantiated; if this process fails then an
142     *   unspecified error is thrown.  </p></li>
143     *
144     *   <li><p> If a provider class has been installed in a jar file that is
145     *   visible to the system class loader, and that jar file contains a
146     *   provider-configuration file named
147     *   <tt>java.nio.channels.spi.SelectorProvider</tt> in the resource
148     *   directory <tt>META-INF/services</tt>, then the first class name
149     *   specified in that file is taken.  The class is loaded and
150     *   instantiated; if this process fails then an unspecified error is
151     *   thrown.  </p></li>
152     *
153     *   <li><p> Finally, if no provider has been specified by any of the above
154     *   means then the system-default provider class is instantiated and the
155     *   result is returned.  </p></li>
156     *
157     * </ol>
158     *
159     * <p> Subsequent invocations of this method return the provider that was
160     * returned by the first invocation.  </p>
161     *
162     * @return  The system-wide default selector provider
163     */
164    public static SelectorProvider provider() {
165        synchronized (lock) {
166            if (provider != null)
167                return provider;
168            return AccessController.doPrivileged(
169                new PrivilegedAction<SelectorProvider>() {
170                    public SelectorProvider run() {
171                            if (loadProviderFromProperty())
172                                return provider;
173                            if (loadProviderAsService())
174                                return provider;
175                            provider = sun.nio.ch.DefaultSelectorProvider.create();
176                            return provider;
177                        }
178                    });
179        }
180    }
181
182    /**
183     * Opens a datagram channel.  </p>
184     *
185     * @return  The new channel
186     */
187    public abstract DatagramChannel openDatagramChannel()
188        throws IOException;
189
190    /**
191     * Opens a datagram channel.
192     *
193     * @param   family
194     *          The protocol family
195     *
196     * @return  A new datagram channel
197     *
198     * @throws  UnsupportedOperationException
199     *          If the specified protocol family is not supported
200     * @throws  IOException
201     *          If an I/O error occurs
202     *
203     * @since 1.7
204     */
205    public abstract DatagramChannel openDatagramChannel(ProtocolFamily family)
206        throws IOException;
207
208    /**
209     * Opens a pipe. </p>
210     *
211     * @return  The new pipe
212     */
213    public abstract Pipe openPipe()
214        throws IOException;
215
216    /**
217     * Opens a selector.  </p>
218     *
219     * @return  The new selector
220     */
221    public abstract AbstractSelector openSelector()
222        throws IOException;
223
224    /**
225     * Opens a server-socket channel.  </p>
226     *
227     * @return  The new channel
228     */
229    public abstract ServerSocketChannel openServerSocketChannel()
230        throws IOException;
231
232    /**
233     * Opens a socket channel. </p>
234     *
235     * @return  The new channel
236     */
237    public abstract SocketChannel openSocketChannel()
238        throws IOException;
239
240    /**
241     * Returns the channel inherited from the entity that created this
242     * Java virtual machine.
243     *
244     * <p> On many operating systems a process, such as a Java virtual
245     * machine, can be started in a manner that allows the process to
246     * inherit a channel from the entity that created the process. The
247     * manner in which this is done is system dependent, as are the
248     * possible entities to which the channel may be connected. For example,
249     * on UNIX systems, the Internet services daemon (<i>inetd</i>) is used to
250     * start programs to service requests when a request arrives on an
251     * associated network port. In this example, the process that is started,
252     * inherits a channel representing a network socket.
253     *
254     * <p> In cases where the inherited channel represents a network socket
255     * then the {@link java.nio.channels.Channel Channel} type returned
256     * by this method is determined as follows:
257     *
258     * <ul>
259     *
260     *  <li><p> If the inherited channel represents a stream-oriented connected
261     *  socket then a {@link java.nio.channels.SocketChannel SocketChannel} is
262     *  returned. The socket channel is, at least initially, in blocking
263     *  mode, bound to a socket address, and connected to a peer.
264     *  </p></li>
265     *
266     *  <li><p> If the inherited channel represents a stream-oriented listening
267     *  socket then a {@link java.nio.channels.ServerSocketChannel
268     *  ServerSocketChannel} is returned. The server-socket channel is, at
269     *  least initially, in blocking mode, and bound to a socket address.
270     *  </p></li>
271     *
272     *  <li><p> If the inherited channel is a datagram-oriented socket
273     *  then a {@link java.nio.channels.DatagramChannel DatagramChannel} is
274     *  returned. The datagram channel is, at least initially, in blocking
275     *  mode, and bound to a socket address.
276     *  </p></li>
277     *
278     * </ul>
279     *
280     * <p> In addition to the network-oriented channels described, this method
281     * may return other kinds of channels in the future.
282     *
283     * <p> The first invocation of this method creates the channel that is
284     * returned. Subsequent invocations of this method return the same
285     * channel. </p>
286     *
287     * @return  The inherited channel, if any, otherwise <tt>null</tt>.
288     *
289     * @throws  IOException
290     *          If an I/O error occurs
291     *
292     * @throws  SecurityException
293     *          If a security manager has been installed and it denies
294     *          {@link RuntimePermission}<tt>("inheritedChannel")</tt>
295     *
296     * @since 1.5
297     */
298   public Channel inheritedChannel() throws IOException {
299        return null;
300   }
301
302}
303