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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>

 *   </tr>

 *   </thead>

 *   <tbody>

 *   <tr>

 *     <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>

 *     <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;

}