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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.

 An asynchronous channel group encapsulates the mechanics required to handle the completion of I/O operations initiated by 
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 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. 
 An asynchronous channel group is created by invoking the withFixedThreadPool or 
withCachedThreadPool methods defined here. Channels are bound to a group by specifying the group when constructing the channel. The associated thread pool is owned by the group; termination of the group results in the
shutdown of the associated thread pool.

 In addition to groups created explicitly, the Java virtual machine
maintains a system-wide default group 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 ThreadFactory for the default group is not configured then the pooled threads of the default group are daemon threads. 

System properties
  
  

    System property
    Description
  

  
  
  

     java.nio.channels.DefaultThreadPool.threadFactory 
     The value of this property is taken to be the fully-qualified name of a concrete ThreadFactory class. The class is loaded using the system class loader and instantiated. The factory's 
    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. 
  

  

     java.nio.channels.DefaultThreadPool.initialSize 
     The value of the initialSize parameter for the default group (see withCachedThreadPool). The value of the property is taken to be the String representation of an Integer that is the initial size parameter. If the value cannot be parsed as an Integer it causes an unspecified error to be thrown during the construction of the default group. 
  

  



Threading


 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 identity.

 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 accept). 
Shutdown and Termination


 The shutdown method is used to initiate an orderly
shutdown of a group. An orderly shutdown marks the group as shutdown; further attempts to construct a channel that binds to the group will throw ShutdownChannelGroupException. Whether or not a group is shutdown can be tested using the isShutdown method. Once shutdown, the group terminates 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 isTerminated method is used to test if the group has terminated, and the awaitTermination method can be used to block until the group has terminated. 
 The shutdownNow method can be used to initiate a forceful shutdown of the group. In addition to the actions performed by an orderly shutdown, the shutdownNow method closes all open channels in the group as if by invoking the close method. 
See Also:
Since:1.7
/**
 * 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.

Params:
  • provider – 
         The asynchronous channel provider for this group
/**
     * 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.

Returns: The provider that created this channel group
/**
     * 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.

 The resulting asynchronous channel group reuses a fixed number of threads. At any point, at most 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. 
 The group is created by invoking the 
openAsynchronousChannelGroup(int,ThreadFactory) method of the system-wide default AsynchronousChannelProvider object. 
Params:
  • nThreads – 
         The number of threads in the pool
  • threadFactory – 
         The factory to use when creating new threads
Throws:
Returns: A new asynchronous channel group
/**
     * 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.

 The executor parameter is an 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. 
 The initialSize parameter may be used by the implementation as a hint 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.

 The executor is intended to be used exclusively by the resulting asynchronous channel group. Termination of the group results in the orderly shutdown of the executor service. Shutting down the executor service by other means results in unspecified behavior. 
 The group is created by invoking the 
openAsynchronousChannelGroup(ExecutorService,int) method of the system-wide default AsynchronousChannelProvider object. 
Params:
  • executor – 
         The thread pool for the resulting group
  • initialSize –  A value >=0 or a negative value for implementation specific default
Throws:
See Also:
Returns: A new asynchronous channel group
/**
     * 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.

 The executor parameter is an ExecutorService that executes tasks submitted to dispatch completion results for operations initiated on asynchronous channels in the group. 
 Care should be taken when configuring the executor service. It
should support direct handoff or unbounded queuing of submitted tasks, and the thread that invokes the execute method should never invoke the task directly. An implementation may mandate additional constraints. 
 The executor is intended to be used exclusively by the resulting asynchronous channel group. Termination of the group results in the orderly shutdown of the executor service. Shutting down the executor service by other means results in unspecified behavior. 
 The group is created by invoking the 
openAsynchronousChannelGroup(ExecutorService,int) method of the system-wide default AsynchronousChannelProvider object with an 
initialSize of 0. 
Params:
  • executor – 
         The thread pool for the resulting group
Throws:
Returns: A new asynchronous channel group
/**
     * 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.

Returns: true if this asynchronous channel group is shutdown or has been marked for shutdown.
/**
     * 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.

 Where this method returns true, then the associated thread pool has also terminated. 
Returns: true if this group has terminated
/**
     * 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.

 This method marks the group as shutdown. Further attempts to construct channel that binds to this group will throw 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. 
/**
     * 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.

 In addition to the actions performed by the shutdown method, this method invokes the 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:
/**
     * 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.

 This method blocks until the group has terminated, or the timeout
occurs, or the current thread is interrupted, whichever happens first.

Params:
  • timeout – 
         The maximum time to wait, or zero or less to not wait
  • unit – 
         The time unit of the timeout argument
Throws:
Returns: true if the group has terminated; false if the timeout elapsed before termination
/**
     * 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;
}