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/**
* 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 border>
* <tr>
* <th>System property</th>
* <th>Description</th>
* </tr>
* <tr>
* <tr>
* <td> {@code java.nio.channels.DefaultThreadPool.threadFactory} </td>
* <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> {@code java.nio.channels.DefaultThreadPool.initialSize} </td>
* <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>
* </table>
*
* <a name="threading"><h4>Threading</h4></a>
*
* <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 name="shutdown"><h4>Shutdown and Termination</h4></a>
*
* <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 {
/**
* Initialize a new instance of this class.
*
* @param provider
* The asynchronous channel provider for this group
*/
}
/**
* Returns the provider that created this channel group.
*
* @return The provider that created this channel group
*/
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
*/
throws IOException
{
return AsynchronousChannelProvider.provider()
}
/**
* 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 indictae 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
*/
int initialSize)
throws IOException
{
return AsynchronousChannelProvider.provider()
}
/**
* 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
*/
throws IOException
{
return AsynchronousChannelProvider.provider()
}
/**
* 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
*/
/**
* 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
*/
throws InterruptedException;
}