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package java.nio.channels;

import java.io.IOException;
import java.nio.channels.spi.AbstractInterruptibleChannel;
import java.nio.channels.spi.SelectorProvider;



A channel that can be multiplexed via a Selector. 
 In order to be used with a selector, an instance of this class must
first be registered via the 
register method. This method returns a new SelectionKey object that represents the channel's registration with the selector. 
 Once registered with a selector, a channel remains registered until it
is deregistered.  This involves deallocating whatever resources were
allocated to the channel by the selector.

 A channel cannot be deregistered directly; instead, the key representing
its registration must be cancelled. Cancelling a key requests that the channel be deregistered during the selector's next selection operation. A key may be cancelled explicitly by invoking its cancel method. All of a channel's keys are cancelled implicitly when the channel is closed, whether by invoking its close method or by interrupting a thread blocked in an I/O operation upon the channel. 
 If the selector itself is closed then the channel will be deregistered,
and the key representing its registration will be invalidated, without
further delay.

 A channel may be registered at most once with any particular selector.

 Whether or not a channel is registered with one or more selectors may be determined by invoking the isRegistered method. 
 Selectable channels are safe for use by multiple concurrent
threads. 



Blocking mode

A selectable channel is either in blocking mode or in
non-blocking mode. In blocking mode, every I/O operation invoked upon the channel will block until it completes. In non-blocking mode an I/O operation will never block and may transfer fewer bytes than were requested or possibly no bytes at all. The blocking mode of a selectable channel may be determined by invoking its isBlocking method. 
 Newly-created selectable channels are always in blocking mode.
Non-blocking mode is most useful in conjunction with selector-based
multiplexing.  A channel must be placed into non-blocking mode before being
registered with a selector, and may not be returned to blocking mode until
it has been deregistered.

Author:Mark Reinhold, JSR-51 Expert Group
See Also:
Since:1.4
/**
 * A channel that can be multiplexed via a {@link Selector}.
 *
 * <p> In order to be used with a selector, an instance of this class must
 * first be <i>registered</i> via the {@link #register(Selector,int,Object)
 * register} method.  This method returns a new {@link SelectionKey} object
 * that represents the channel's registration with the selector.
 *
 * <p> Once registered with a selector, a channel remains registered until it
 * is <i>deregistered</i>.  This involves deallocating whatever resources were
 * allocated to the channel by the selector.
 *
 * <p> A channel cannot be deregistered directly; instead, the key representing
 * its registration must be <i>cancelled</i>.  Cancelling a key requests that
 * the channel be deregistered during the selector's next selection operation.
 * A key may be cancelled explicitly by invoking its {@link
 * SelectionKey#cancel() cancel} method.  All of a channel's keys are cancelled
 * implicitly when the channel is closed, whether by invoking its {@link
 * Channel#close close} method or by interrupting a thread blocked in an I/O
 * operation upon the channel.
 *
 * <p> If the selector itself is closed then the channel will be deregistered,
 * and the key representing its registration will be invalidated, without
 * further delay.
 *
 * <p> A channel may be registered at most once with any particular selector.
 *
 * <p> Whether or not a channel is registered with one or more selectors may be
 * determined by invoking the {@link #isRegistered isRegistered} method.
 *
 * <p> Selectable channels are safe for use by multiple concurrent
 * threads. </p>
 *
 *
 * <a id="bm"></a>
 * <h2>Blocking mode</h2>
 *
 * A selectable channel is either in <i>blocking</i> mode or in
 * <i>non-blocking</i> mode.  In blocking mode, every I/O operation invoked
 * upon the channel will block until it completes.  In non-blocking mode an I/O
 * operation will never block and may transfer fewer bytes than were requested
 * or possibly no bytes at all.  The blocking mode of a selectable channel may
 * be determined by invoking its {@link #isBlocking isBlocking} method.
 *
 * <p> Newly-created selectable channels are always in blocking mode.
 * Non-blocking mode is most useful in conjunction with selector-based
 * multiplexing.  A channel must be placed into non-blocking mode before being
 * registered with a selector, and may not be returned to blocking mode until
 * it has been deregistered.
 *
 *
 * @author Mark Reinhold
 * @author JSR-51 Expert Group
 * @since 1.4
 *
 * @see SelectionKey
 * @see Selector
 */

public abstract class SelectableChannel
    extends AbstractInterruptibleChannel
    implements Channel
{

    
Initializes a new instance of this class.

/**
     * Initializes a new instance of this class.
     */
    protected SelectableChannel() { }

    
Returns the provider that created this channel.

Returns: The provider that created this channel
/**
     * Returns the provider that created this channel.
     *
     * @return  The provider that created this channel
     */
    public abstract SelectorProvider provider();

    
Returns an operation set
identifying this channel's supported operations.  The bits that are set
in this integer value denote exactly the operations that are valid for
this channel.  This method always returns the same value for a given
concrete channel class.

Returns: The valid-operation set
/**
     * Returns an <a href="SelectionKey.html#opsets">operation set</a>
     * identifying this channel's supported operations.  The bits that are set
     * in this integer value denote exactly the operations that are valid for
     * this channel.  This method always returns the same value for a given
     * concrete channel class.
     *
     * @return  The valid-operation set
     */
    public abstract int validOps();

    
Tells whether or not this channel is currently registered with any
selectors.  A newly-created channel is not registered.

 Due to the inherent delay between key cancellation and channel
deregistration, a channel may remain registered for some time after all
of its keys have been cancelled.  A channel may also remain registered
for some time after it is closed.  


Returns:true if, and only if, this channel is registered
/**
     * Tells whether or not this channel is currently registered with any
     * selectors.  A newly-created channel is not registered.
     *
     * <p> Due to the inherent delay between key cancellation and channel
     * deregistration, a channel may remain registered for some time after all
     * of its keys have been cancelled.  A channel may also remain registered
     * for some time after it is closed.  </p>
     *
     * @return {@code true} if, and only if, this channel is registered
     */
    public abstract boolean isRegistered();

    
Retrieves the key representing the channel's registration with the given
selector.

Params:
  • sel – 
         The selector
Returns: The key returned when this channel was last registered with the given selector, or null if this channel is not currently registered with that selector
/**
     * Retrieves the key representing the channel's registration with the given
     * selector.
     *
     * @param   sel
     *          The selector
     *
     * @return  The key returned when this channel was last registered with the
     *          given selector, or {@code null} if this channel is not
     *          currently registered with that selector
     */
    public abstract SelectionKey keyFor(Selector sel);

    
Registers this channel with the given selector, returning a selection
key.

 If this channel is currently registered with the given selector then the selection key representing that registration is returned. The key's interest set will have been changed to ops, as if by invoking the interestOps(int) method. If the att argument is not null then the key's attachment will have been set to that value. A CancelledKeyException will be thrown if the key has already been cancelled. 
 Otherwise this channel has not yet been registered with the given selector, so it is registered and the resulting new key is returned. The key's initial interest set will be ops and its attachment will be att. 
 This method may be invoked at any time. If this method is invoked while a selection operation is in progress then it has no effect upon that operation; the new registration or change to the key's interest set will be seen by the next selection operation. If this method is invoked while an invocation of configureBlocking is in progress then it will block until the channel's blocking mode has been adjusted. 
 If this channel is closed while this operation is in progress then
the key returned by this method will have been cancelled and will
therefore be invalid. 


Params:
  • sel – 
        The selector with which this channel is to be registered
  • ops – 
        The interest set for the resulting key
  • att –  The attachment for the resulting key; may be null
Throws:
Returns: A key representing the registration of this channel with
         the given selector
/**
     * Registers this channel with the given selector, returning a selection
     * key.
     *
     * <p> If this channel is currently registered with the given selector then
     * the selection key representing that registration is returned.  The key's
     * interest set will have been changed to {@code ops}, as if by invoking
     * the {@link SelectionKey#interestOps(int) interestOps(int)} method.  If
     * the {@code att} argument is not {@code null} then the key's attachment
     * will have been set to that value.  A {@link CancelledKeyException} will
     * be thrown if the key has already been cancelled.
     *
     * <p> Otherwise this channel has not yet been registered with the given
     * selector, so it is registered and the resulting new key is returned.
     * The key's initial interest set will be {@code ops} and its attachment
     * will be {@code att}.
     *
     * <p> This method may be invoked at any time.  If this method is invoked
     * while a selection operation is in progress then it has no effect upon
     * that operation; the new registration or change to the key's interest set
     * will be seen by the next selection operation.  If this method is invoked
     * while an invocation of {@link #configureBlocking(boolean) configureBlocking}
     * is in progress then it will block until the channel's blocking mode has
     * been adjusted.
     *
     * <p> If this channel is closed while this operation is in progress then
     * the key returned by this method will have been cancelled and will
     * therefore be invalid. </p>
     *
     * @param  sel
     *         The selector with which this channel is to be registered
     *
     * @param  ops
     *         The interest set for the resulting key
     *
     * @param  att
     *         The attachment for the resulting key; may be {@code null}
     *
     * @throws  ClosedChannelException
     *          If this channel is closed
     *
     * @throws  ClosedSelectorException
     *          If the selector is closed
     *
     * @throws  IllegalBlockingModeException
     *          If this channel is in blocking mode
     *
     * @throws  IllegalSelectorException
     *          If this channel was not created by the same provider
     *          as the given selector
     *
     * @throws  CancelledKeyException
     *          If this channel is currently registered with the given selector
     *          but the corresponding key has already been cancelled
     *
     * @throws  IllegalArgumentException
     *          If a bit in the {@code ops} set does not correspond to an
     *          operation that is supported by this channel, that is, if
     *          {@code set & ~validOps() != 0}
     *
     * @return  A key representing the registration of this channel with
     *          the given selector
     */
    public abstract SelectionKey register(Selector sel, int ops, Object att)
        throws ClosedChannelException;

    
Registers this channel with the given selector, returning a selection
key.

 An invocation of this convenience method of the form

sc.register(sel, ops)

behaves in exactly the same way as the invocation

sc.
register(sel, ops, null)


Params:
  • sel – 
        The selector with which this channel is to be registered
  • ops – 
        The interest set for the resulting key
Throws:
Returns: A key representing the registration of this channel with
         the given selector
/**
     * Registers this channel with the given selector, returning a selection
     * key.
     *
     * <p> An invocation of this convenience method of the form
     *
     * <blockquote>{@code sc.register(sel, ops)}</blockquote>
     *
     * behaves in exactly the same way as the invocation
     *
     * <blockquote>{@code sc.}{@link
     * #register(java.nio.channels.Selector,int,java.lang.Object)
     * register(sel, ops, null)}</blockquote>
     *
     * @param  sel
     *         The selector with which this channel is to be registered
     *
     * @param  ops
     *         The interest set for the resulting key
     *
     * @throws  ClosedChannelException
     *          If this channel is closed
     *
     * @throws  ClosedSelectorException
     *          If the selector is closed
     *
     * @throws  IllegalBlockingModeException
     *          If this channel is in blocking mode
     *
     * @throws  IllegalSelectorException
     *          If this channel was not created by the same provider
     *          as the given selector
     *
     * @throws  CancelledKeyException
     *          If this channel is currently registered with the given selector
     *          but the corresponding key has already been cancelled
     *
     * @throws  IllegalArgumentException
     *          If a bit in {@code ops} does not correspond to an operation
     *          that is supported by this channel, that is, if {@code set &
     *          ~validOps() != 0}
     *
     * @return  A key representing the registration of this channel with
     *          the given selector
     */
    public final SelectionKey register(Selector sel, int ops)
        throws ClosedChannelException
    {
        return register(sel, ops, null);
    }

    
Adjusts this channel's blocking mode.

 If this channel is registered with one or more selectors then an attempt to place it into blocking mode will cause an IllegalBlockingModeException to be thrown. 
 This method may be invoked at any time.  The new blocking mode will
only affect I/O operations that are initiated after this method returns.
For some implementations this may require blocking until all pending I/O
operations are complete.

 If this method is invoked while another invocation of this method or of the register method is in progress then it will first block until the other operation is complete. 


Params:
  • block –  If true then this channel will be placed in blocking mode; if false then it will be placed non-blocking mode
Throws:
Returns: This selectable channel
/**
     * Adjusts this channel's blocking mode.
     *
     * <p> If this channel is registered with one or more selectors then an
     * attempt to place it into blocking mode will cause an {@link
     * IllegalBlockingModeException} to be thrown.
     *
     * <p> This method may be invoked at any time.  The new blocking mode will
     * only affect I/O operations that are initiated after this method returns.
     * For some implementations this may require blocking until all pending I/O
     * operations are complete.
     *
     * <p> If this method is invoked while another invocation of this method or
     * of the {@link #register(Selector, int) register} method is in progress
     * then it will first block until the other operation is complete. </p>
     *
     * @param  block  If {@code true} then this channel will be placed in
     *                blocking mode; if {@code false} then it will be placed
     *                non-blocking mode
     *
     * @return  This selectable channel
     *
     * @throws  ClosedChannelException
     *          If this channel is closed
     *
     * @throws  IllegalBlockingModeException
     *          If {@code block} is {@code true} and this channel is
     *          registered with one or more selectors
     *
     * @throws IOException
     *         If an I/O error occurs
     */
    public abstract SelectableChannel configureBlocking(boolean block)
        throws IOException;

    
Tells whether or not every I/O operation on this channel will block
until it completes.  A newly-created channel is always in blocking mode.

 If this channel is closed then the value returned by this method is
not specified. 


Returns:true if, and only if, this channel is in blocking mode
/**
     * Tells whether or not every I/O operation on this channel will block
     * until it completes.  A newly-created channel is always in blocking mode.
     *
     * <p> If this channel is closed then the value returned by this method is
     * not specified. </p>
     *
     * @return {@code true} if, and only if, this channel is in blocking mode
     */
    public abstract boolean isBlocking();

    
Retrieves the object upon which the 
configureBlocking and register methods synchronize. This is often useful in the implementation of adaptors that require a specific blocking mode to be maintained for a short period of time. 
Returns: The blocking-mode lock object
/**
     * Retrieves the object upon which the {@link #configureBlocking
     * configureBlocking} and {@link #register register} methods synchronize.
     * This is often useful in the implementation of adaptors that require a
     * specific blocking mode to be maintained for a short period of time.
     *
     * @return  The blocking-mode lock object
     */
    public abstract Object blockingLock();

}