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	/*
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	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
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	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
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	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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	package java.nio.channels;

	import java.nio.channels.spi.AsynchronousChannelProvider;
	import java.io.IOException;
	import java.util.concurrent.ExecutorService;
	import java.util.concurrent.ThreadFactory;
	import java.util.concurrent.TimeUnit;

	/**
	* A grouping of asynchronous channels for the purpose of resource sharing.
	*
	* <p> An asynchronous channel group encapsulates the mechanics required to
	* handle the completion of I/O operations initiated by {@link AsynchronousChannel
	* asynchronous channels} that are bound to the group. A group has an associated
	* thread pool to which tasks are submitted to handle I/O events and dispatch to
	* {@link CompletionHandler completion-handlers} that consume the result of
	* asynchronous operations performed on channels in the group. In addition to
	* handling I/O events, the pooled threads may also execute other tasks required
	* to support the execution of asynchronous I/O operations.
	*
	* <p> An asynchronous channel group is created by invoking the {@link
	* #withFixedThreadPool withFixedThreadPool} or {@link #withCachedThreadPool
	* withCachedThreadPool} methods defined here. Channels are bound to a group by
	* specifying the group when constructing the channel. The associated thread
	* pool is <em>owned</em> by the group; termination of the group results in the
	* shutdown of the associated thread pool.
	*
	* <p> In addition to groups created explicitly, the Java virtual machine
	* maintains a system-wide <em>default group</em> that is constructed
	* automatically. Asynchronous channels that do not specify a group at
	* construction time are bound to the default group. The default group has an
	* associated thread pool that creates new threads as needed. The default group
	* may be configured by means of system properties defined in the table below.
	* Where the {@link java.util.concurrent.ThreadFactory ThreadFactory} for the
	* default group is not configured then the pooled threads of the default group
	* are {@link Thread#isDaemon daemon} threads.
	*
	* <table class="striped">
	* <caption style="display:none:">System properties</caption>
	* <thead>
	* <tr>
	* <th scope="col">System property</th>
	* <th scope="col">Description</th>
	* </tr>
	* </thead>
	* <tbody>
	* <tr>
	* <th scope="row"> {@code java.nio.channels.DefaultThreadPool.threadFactory} </th>
	* <td> The value of this property is taken to be the fully-qualified name
	* of a concrete {@link java.util.concurrent.ThreadFactory ThreadFactory}
	* class. The class is loaded using the system class loader and instantiated.
	* The factory's {@link java.util.concurrent.ThreadFactory#newThread
	* newThread} method is invoked to create each thread for the default
	* group's thread pool. If the process to load and instantiate the value
	* of the property fails then an unspecified error is thrown during the
	* construction of the default group. </td>
	* </tr>
	* <tr>
	* <th scope="row"> {@code java.nio.channels.DefaultThreadPool.initialSize} </th>
	* <td> The value of the {@code initialSize} parameter for the default
	* group (see {@link #withCachedThreadPool withCachedThreadPool}).
	* The value of the property is taken to be the {@code String}
	* representation of an {@code Integer} that is the initial size parameter.
	* If the value cannot be parsed as an {@code Integer} it causes an
	* unspecified error to be thrown during the construction of the default
	* group. </td>
	* </tr>
	* </tbody>
	* </table>
	*
	* <a id="threading"></a><h2>Threading</h2>
	*
	* <p> The completion handler for an I/O operation initiated on a channel bound
	* to a group is guaranteed to be invoked by one of the pooled threads in the
	* group. This ensures that the completion handler is run by a thread with the
	* expected <em>identity</em>.
	*
	* <p> Where an I/O operation completes immediately, and the initiating thread
	* is one of the pooled threads in the group then the completion handler may
	* be invoked directly by the initiating thread. To avoid stack overflow, an
	* implementation may impose a limit as to the number of activations on the
	* thread stack. Some I/O operations may prohibit invoking the completion
	* handler directly by the initiating thread (see {@link
	* AsynchronousServerSocketChannel#accept(Object,CompletionHandler) accept}).
	*
	* <a id="shutdown"></a><h2>Shutdown and Termination</h2>
	*
	* <p> The {@link #shutdown() shutdown} method is used to initiate an <em>orderly
	* shutdown</em> of a group. An orderly shutdown marks the group as shutdown;
	* further attempts to construct a channel that binds to the group will throw
	* {@link ShutdownChannelGroupException}. Whether or not a group is shutdown can
	* be tested using the {@link #isShutdown() isShutdown} method. Once shutdown,
	* the group <em>terminates</em> when all asynchronous channels that are bound to
	* the group are closed, all actively executing completion handlers have run to
	* completion, and resources used by the group are released. No attempt is made
	* to stop or interrupt threads that are executing completion handlers. The
	* {@link #isTerminated() isTerminated} method is used to test if the group has
	* terminated, and the {@link #awaitTermination awaitTermination} method can be
	* used to block until the group has terminated.
	*
	* <p> The {@link #shutdownNow() shutdownNow} method can be used to initiate a
	* <em>forceful shutdown</em> of the group. In addition to the actions performed
	* by an orderly shutdown, the {@code shutdownNow} method closes all open channels
	* in the group as if by invoking the {@link AsynchronousChannel#close close}
	* method.
	*
	* @since 1.7
	*
	* @see AsynchronousSocketChannel#open(AsynchronousChannelGroup)
	* @see AsynchronousServerSocketChannel#open(AsynchronousChannelGroup)
	*/

	public abstract class AsynchronousChannelGroup {
	private final AsynchronousChannelProvider provider;

	/**
	* Initialize a new instance of this class.
	*
	* @param provider
	* The asynchronous channel provider for this group
	*/
	protected AsynchronousChannelGroup(AsynchronousChannelProvider provider) {
	this.provider = provider;
	}

	/**
	* Returns the provider that created this channel group.
	*
	* @return The provider that created this channel group
	*/
	public final AsynchronousChannelProvider provider() {
	return provider;
	}

	/**
	* Creates an asynchronous channel group with a fixed thread pool.
	*
	* <p> The resulting asynchronous channel group reuses a fixed number of
	* threads. At any point, at most {@code nThreads} threads will be active
	* processing tasks that are submitted to handle I/O events and dispatch
	* completion results for operations initiated on asynchronous channels in
	* the group.
	*
	* <p> The group is created by invoking the {@link
	* AsynchronousChannelProvider#openAsynchronousChannelGroup(int,ThreadFactory)
	* openAsynchronousChannelGroup(int,ThreadFactory)} method of the system-wide
	* default {@link AsynchronousChannelProvider} object.
	*
	* @param nThreads
	* The number of threads in the pool
	* @param threadFactory
	* The factory to use when creating new threads
	*
	* @return A new asynchronous channel group
	*
	* @throws IllegalArgumentException
	* If {@code nThreads <= 0}
	* @throws IOException
	* If an I/O error occurs
	*/
	public static AsynchronousChannelGroup withFixedThreadPool(int nThreads,
	ThreadFactory threadFactory)
	throws IOException
	{
	return AsynchronousChannelProvider.provider()
	.openAsynchronousChannelGroup(nThreads, threadFactory);
	}

	/**
	* Creates an asynchronous channel group with a given thread pool that
	* creates new threads as needed.
	*
	* <p> The {@code executor} parameter is an {@code ExecutorService} that
	* creates new threads as needed to execute tasks that are submitted to
	* handle I/O events and dispatch completion results for operations initiated
	* on asynchronous channels in the group. It may reuse previously constructed
	* threads when they are available.
	*
	* <p> The {@code initialSize} parameter may be used by the implementation
	* as a <em>hint</em> as to the initial number of tasks it may submit. For
	* example, it may be used to indicate the initial number of threads that
	* wait on I/O events.
	*
	* <p> The executor is intended to be used exclusively by the resulting
	* asynchronous channel group. Termination of the group results in the
	* orderly {@link ExecutorService#shutdown shutdown} of the executor
	* service. Shutting down the executor service by other means results in
	* unspecified behavior.
	*
	* <p> The group is created by invoking the {@link
	* AsynchronousChannelProvider#openAsynchronousChannelGroup(ExecutorService,int)
	* openAsynchronousChannelGroup(ExecutorService,int)} method of the system-wide
	* default {@link AsynchronousChannelProvider} object.
	*
	* @param executor
	* The thread pool for the resulting group
	* @param initialSize
	* A value {@code >=0} or a negative value for implementation
	* specific default
	*
	* @return A new asynchronous channel group
	*
	* @throws IOException
	* If an I/O error occurs
	*
	* @see java.util.concurrent.Executors#newCachedThreadPool
	*/
	public static AsynchronousChannelGroup withCachedThreadPool(ExecutorService executor,
	int initialSize)
	throws IOException
	{
	return AsynchronousChannelProvider.provider()
	.openAsynchronousChannelGroup(executor, initialSize);
	}

	/**
	* Creates an asynchronous channel group with a given thread pool.
	*
	* <p> The {@code executor} parameter is an {@code ExecutorService} that
	* executes tasks submitted to dispatch completion results for operations
	* initiated on asynchronous channels in the group.
	*
	* <p> Care should be taken when configuring the executor service. It
	* should support <em>direct handoff</em> or <em>unbounded queuing</em> of
	* submitted tasks, and the thread that invokes the {@link
	* ExecutorService#execute execute} method should never invoke the task
	* directly. An implementation may mandate additional constraints.
	*
	* <p> The executor is intended to be used exclusively by the resulting
	* asynchronous channel group. Termination of the group results in the
	* orderly {@link ExecutorService#shutdown shutdown} of the executor
	* service. Shutting down the executor service by other means results in
	* unspecified behavior.
	*
	* <p> The group is created by invoking the {@link
	* AsynchronousChannelProvider#openAsynchronousChannelGroup(ExecutorService,int)
	* openAsynchronousChannelGroup(ExecutorService,int)} method of the system-wide
	* default {@link AsynchronousChannelProvider} object with an {@code
	* initialSize} of {@code 0}.
	*
	* @param executor
	* The thread pool for the resulting group
	*
	* @return A new asynchronous channel group
	*
	* @throws IOException
	* If an I/O error occurs
	*/
	public static AsynchronousChannelGroup withThreadPool(ExecutorService executor)
	throws IOException
	{
	return AsynchronousChannelProvider.provider()
	.openAsynchronousChannelGroup(executor, 0);
	}

	/**
	* Tells whether or not this asynchronous channel group is shutdown.
	*
	* @return {@code true} if this asynchronous channel group is shutdown or
	* has been marked for shutdown.
	*/
	public abstract boolean isShutdown();

	/**
	* Tells whether or not this group has terminated.
	*
	* <p> Where this method returns {@code true}, then the associated thread
	* pool has also {@link ExecutorService#isTerminated terminated}.
	*
	* @return {@code true} if this group has terminated
	*/
	public abstract boolean isTerminated();

	/**
	* Initiates an orderly shutdown of the group.
	*
	* <p> This method marks the group as shutdown. Further attempts to construct
	* channel that binds to this group will throw {@link ShutdownChannelGroupException}.
	* The group terminates when all asynchronous channels in the group are
	* closed, all actively executing completion handlers have run to completion,
	* and all resources have been released. This method has no effect if the
	* group is already shutdown.
	*/
	public abstract void shutdown();

	/**
	* Shuts down the group and closes all open channels in the group.
	*
	* <p> In addition to the actions performed by the {@link #shutdown() shutdown}
	* method, this method invokes the {@link AsynchronousChannel#close close}
	* method on all open channels in the group. This method does not attempt to
	* stop or interrupt threads that are executing completion handlers. The
	* group terminates when all actively executing completion handlers have run
	* to completion and all resources have been released. This method may be
	* invoked at any time. If some other thread has already invoked it, then
	* another invocation will block until the first invocation is complete,
	* after which it will return without effect.
	*
	* @throws IOException
	* If an I/O error occurs
	*/
	public abstract void shutdownNow() throws IOException;

	/**
	* Awaits termination of the group.

	* <p> This method blocks until the group has terminated, or the timeout
	* occurs, or the current thread is interrupted, whichever happens first.
	*
	* @param timeout
	* The maximum time to wait, or zero or less to not wait
	* @param unit
	* The time unit of the timeout argument
	*
	* @return {@code true} if the group has terminated; {@code false} if the
	* timeout elapsed before termination
	*
	* @throws InterruptedException
	* If interrupted while waiting
	*/
	public abstract boolean awaitTermination(long timeout, TimeUnit unit)
	throws InterruptedException;
	}

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