1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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10 *
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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).
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25
26 package java.nio.channels;
27
28 import java.nio.channels.spi.AsynchronousChannelProvider;
29 import java.io.IOException;
30 import java.util.concurrent.ExecutorService;
31 import java.util.concurrent.ThreadFactory;
32 import java.util.concurrent.TimeUnit;
33
34 /**
35 * A grouping of asynchronous channels for the purpose of resource sharing.
36 *
37 * <p> An asynchronous channel group encapsulates the mechanics required to
38 * handle the completion of I/O operations initiated by {@link AsynchronousChannel
39 * asynchronous channels} that are bound to the group. A group has an associated
40 * thread pool to which tasks are submitted to handle I/O events and dispatch to
41 * {@link CompletionHandler completion-handlers} that consume the result of
42 * asynchronous operations performed on channels in the group. In addition to
43 * handling I/O events, the pooled threads may also execute other tasks required
44 * to support the execution of asynchronous I/O operations.
45 *
46 * <p> An asynchronous channel group is created by invoking the {@link
47 * #withFixedThreadPool withFixedThreadPool} or {@link #withCachedThreadPool
48 * withCachedThreadPool} methods defined here. Channels are bound to a group by
49 * specifying the group when constructing the channel. The associated thread
50 * pool is <em>owned</em> by the group; termination of the group results in the
51 * shutdown of the associated thread pool.
52 *
53 * <p> In addition to groups created explicitly, the Java virtual machine
54 * maintains a system-wide <em>default group</em> that is constructed
55 * automatically. Asynchronous channels that do not specify a group at
56 * construction time are bound to the default group. The default group has an
57 * associated thread pool that creates new threads as needed. The default group
58 * may be configured by means of system properties defined in the table below.
59 * Where the {@link java.util.concurrent.ThreadFactory ThreadFactory} for the
60 * default group is not configured then the pooled threads of the default group
61 * are {@link Thread#isDaemon daemon} threads.
62 *
63 * <table border summary="System properties">
64 * <tr>
65 * <th>System property</th>
66 * <th>Description</th>
67 * </tr>
68 * <tr>
69 * <td> {@code java.nio.channels.DefaultThreadPool.threadFactory} </td>
70 * <td> The value of this property is taken to be the fully-qualified name
71 * of a concrete {@link java.util.concurrent.ThreadFactory ThreadFactory}
72 * class. The class is loaded using the system class loader and instantiated.
73 * The factory's {@link java.util.concurrent.ThreadFactory#newThread
74 * newThread} method is invoked to create each thread for the default
75 * group's thread pool. If the process to load and instantiate the value
76 * of the property fails then an unspecified error is thrown during the
77 * construction of the default group. </td>
78 * </tr>
79 * <tr>
80 * <td> {@code java.nio.channels.DefaultThreadPool.initialSize} </td>
81 * <td> The value of the {@code initialSize} parameter for the default
82 * group (see {@link #withCachedThreadPool withCachedThreadPool}).
83 * The value of the property is taken to be the {@code String}
84 * representation of an {@code Integer} that is the initial size parameter.
85 * If the value cannot be parsed as an {@code Integer} it causes an
86 * unspecified error to be thrown during the construction of the default
87 * group. </td>
88 * </tr>
89 * </table>
90 *
91 * <a id="threading"></a><h2>Threading</h2>
92 *
93 * <p> The completion handler for an I/O operation initiated on a channel bound
94 * to a group is guaranteed to be invoked by one of the pooled threads in the
95 * group. This ensures that the completion handler is run by a thread with the
96 * expected <em>identity</em>.
97 *
98 * <p> Where an I/O operation completes immediately, and the initiating thread
99 * is one of the pooled threads in the group then the completion handler may
100 * be invoked directly by the initiating thread. To avoid stack overflow, an
101 * implementation may impose a limit as to the number of activations on the
102 * thread stack. Some I/O operations may prohibit invoking the completion
103 * handler directly by the initiating thread (see {@link
104 * AsynchronousServerSocketChannel#accept(Object,CompletionHandler) accept}).
105 *
106 * <a id="shutdown"></a><h2>Shutdown and Termination</h2>
107 *
108 * <p> The {@link #shutdown() shutdown} method is used to initiate an <em>orderly
109 * shutdown</em> of a group. An orderly shutdown marks the group as shutdown;
110 * further attempts to construct a channel that binds to the group will throw
111 * {@link ShutdownChannelGroupException}. Whether or not a group is shutdown can
112 * be tested using the {@link #isShutdown() isShutdown} method. Once shutdown,
113 * the group <em>terminates</em> when all asynchronous channels that are bound to
114 * the group are closed, all actively executing completion handlers have run to
115 * completion, and resources used by the group are released. No attempt is made
116 * to stop or interrupt threads that are executing completion handlers. The
117 * {@link #isTerminated() isTerminated} method is used to test if the group has
118 * terminated, and the {@link #awaitTermination awaitTermination} method can be
119 * used to block until the group has terminated.
120 *
121 * <p> The {@link #shutdownNow() shutdownNow} method can be used to initiate a
122 * <em>forceful shutdown</em> of the group. In addition to the actions performed
123 * by an orderly shutdown, the {@code shutdownNow} method closes all open channels
124 * in the group as if by invoking the {@link AsynchronousChannel#close close}
125 * method.
126 *
127 * @since 1.7
128 *
129 * @see AsynchronousSocketChannel#open(AsynchronousChannelGroup)
130 * @see AsynchronousServerSocketChannel#open(AsynchronousChannelGroup)
131 */
132
133 public abstract class AsynchronousChannelGroup {
134 private final AsynchronousChannelProvider provider;
135
136 /**
137 * Initialize a new instance of this class.
138 *
139 * @param provider
140 * The asynchronous channel provider for this group
141 */
142 protected AsynchronousChannelGroup(AsynchronousChannelProvider provider) {
143 this.provider = provider;
144 }
145
146 /**
147 * Returns the provider that created this channel group.
148 *
149 * @return The provider that created this channel group
150 */
151 public final AsynchronousChannelProvider provider() {
152 return provider;
153 }
154
155 /**
156 * Creates an asynchronous channel group with a fixed thread pool.
157 *
158 * <p> The resulting asynchronous channel group reuses a fixed number of
159 * threads. At any point, at most {@code nThreads} threads will be active
160 * processing tasks that are submitted to handle I/O events and dispatch
161 * completion results for operations initiated on asynchronous channels in
162 * the group.
163 *
164 * <p> The group is created by invoking the {@link
165 * AsynchronousChannelProvider#openAsynchronousChannelGroup(int,ThreadFactory)
166 * openAsynchronousChannelGroup(int,ThreadFactory)} method of the system-wide
167 * default {@link AsynchronousChannelProvider} object.
168 *
169 * @param nThreads
170 * The number of threads in the pool
171 * @param threadFactory
172 * The factory to use when creating new threads
173 *
174 * @return A new asynchronous channel group
175 *
176 * @throws IllegalArgumentException
177 * If {@code nThreads <= 0}
178 * @throws IOException
179 * If an I/O error occurs
180 */
181 public static AsynchronousChannelGroup withFixedThreadPool(int nThreads,
182 ThreadFactory threadFactory)
183 throws IOException
184 {
185 return AsynchronousChannelProvider.provider()
186 .openAsynchronousChannelGroup(nThreads, threadFactory);
187 }
188
189 /**
190 * Creates an asynchronous channel group with a given thread pool that
191 * creates new threads as needed.
192 *
193 * <p> The {@code executor} parameter is an {@code ExecutorService} that
194 * creates new threads as needed to execute tasks that are submitted to
195 * handle I/O events and dispatch completion results for operations initiated
196 * on asynchronous channels in the group. It may reuse previously constructed
197 * threads when they are available.
198 *
199 * <p> The {@code initialSize} parameter may be used by the implementation
200 * as a <em>hint</em> as to the initial number of tasks it may submit. For
201 * example, it may be used to indicate the initial number of threads that
202 * wait on I/O events.
203 *
204 * <p> The executor is intended to be used exclusively by the resulting
205 * asynchronous channel group. Termination of the group results in the
206 * orderly {@link ExecutorService#shutdown shutdown} of the executor
207 * service. Shutting down the executor service by other means results in
208 * unspecified behavior.
209 *
210 * <p> The group is created by invoking the {@link
211 * AsynchronousChannelProvider#openAsynchronousChannelGroup(ExecutorService,int)
212 * openAsynchronousChannelGroup(ExecutorService,int)} method of the system-wide
213 * default {@link AsynchronousChannelProvider} object.
214 *
215 * @param executor
216 * The thread pool for the resulting group
217 * @param initialSize
218 * A value {@code >=0} or a negative value for implementation
219 * specific default
220 *
221 * @return A new asynchronous channel group
222 *
223 * @throws IOException
224 * If an I/O error occurs
225 *
226 * @see java.util.concurrent.Executors#newCachedThreadPool
227 */
228 public static AsynchronousChannelGroup withCachedThreadPool(ExecutorService executor,
229 int initialSize)
230 throws IOException
231 {
232 return AsynchronousChannelProvider.provider()
233 .openAsynchronousChannelGroup(executor, initialSize);
234 }
235
236 /**
237 * Creates an asynchronous channel group with a given thread pool.
238 *
239 * <p> The {@code executor} parameter is an {@code ExecutorService} that
240 * executes tasks submitted to dispatch completion results for operations
241 * initiated on asynchronous channels in the group.
242 *
243 * <p> Care should be taken when configuring the executor service. It
244 * should support <em>direct handoff</em> or <em>unbounded queuing</em> of
245 * submitted tasks, and the thread that invokes the {@link
246 * ExecutorService#execute execute} method should never invoke the task
247 * directly. An implementation may mandate additional constraints.
248 *
249 * <p> The executor is intended to be used exclusively by the resulting
250 * asynchronous channel group. Termination of the group results in the
251 * orderly {@link ExecutorService#shutdown shutdown} of the executor
252 * service. Shutting down the executor service by other means results in
253 * unspecified behavior.
254 *
255 * <p> The group is created by invoking the {@link
256 * AsynchronousChannelProvider#openAsynchronousChannelGroup(ExecutorService,int)
257 * openAsynchronousChannelGroup(ExecutorService,int)} method of the system-wide
258 * default {@link AsynchronousChannelProvider} object with an {@code
259 * initialSize} of {@code 0}.
260 *
261 * @param executor
262 * The thread pool for the resulting group
263 *
264 * @return A new asynchronous channel group
265 *
266 * @throws IOException
267 * If an I/O error occurs
268 */
269 public static AsynchronousChannelGroup withThreadPool(ExecutorService executor)
270 throws IOException
271 {
272 return AsynchronousChannelProvider.provider()
273 .openAsynchronousChannelGroup(executor, 0);
274 }
275
276 /**
277 * Tells whether or not this asynchronous channel group is shutdown.
278 *
279 * @return {@code true} if this asynchronous channel group is shutdown or
280 * has been marked for shutdown.
281 */
282 public abstract boolean isShutdown();
283
284 /**
285 * Tells whether or not this group has terminated.
286 *
287 * <p> Where this method returns {@code true}, then the associated thread
288 * pool has also {@link ExecutorService#isTerminated terminated}.
289 *
290 * @return {@code true} if this group has terminated
291 */
292 public abstract boolean isTerminated();
293
294 /**
295 * Initiates an orderly shutdown of the group.
296 *
297 * <p> This method marks the group as shutdown. Further attempts to construct
298 * channel that binds to this group will throw {@link ShutdownChannelGroupException}.
299 * The group terminates when all asynchronous channels in the group are
300 * closed, all actively executing completion handlers have run to completion,
301 * and all resources have been released. This method has no effect if the
302 * group is already shutdown.
303 */
304 public abstract void shutdown();
305
306 /**
307 * Shuts down the group and closes all open channels in the group.
308 *
309 * <p> In addition to the actions performed by the {@link #shutdown() shutdown}
310 * method, this method invokes the {@link AsynchronousChannel#close close}
311 * method on all open channels in the group. This method does not attempt to
312 * stop or interrupt threads that are executing completion handlers. The
313 * group terminates when all actively executing completion handlers have run
314 * to completion and all resources have been released. This method may be
315 * invoked at any time. If some other thread has already invoked it, then
316 * another invocation will block until the first invocation is complete,
317 * after which it will return without effect.
318 *
319 * @throws IOException
320 * If an I/O error occurs
321 */
322 public abstract void shutdownNow() throws IOException;
323
324 /**
325 * Awaits termination of the group.
326
327 * <p> This method blocks until the group has terminated, or the timeout
328 * occurs, or the current thread is interrupted, whichever happens first.
329 *
330 * @param timeout
331 * The maximum time to wait, or zero or less to not wait
332 * @param unit
333 * The time unit of the timeout argument
334 *
335 * @return {@code true} if the group has terminated; {@code false} if the
336 * timeout elapsed before termination
337 *
338 * @throws InterruptedException
339 * If interrupted while waiting
340 */
341 public abstract boolean awaitTermination(long timeout, TimeUnit unit)
342 throws InterruptedException;
343 }