/*
* Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* 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
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
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 {@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 name="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.
*/
protected SelectableChannel() { }
/**
* Returns the provider that created this channel.
*
* @return The provider that created this channel
*/
public abstract SelectorProvider provider();
/**
* 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();
// Internal state:
// keySet, may be empty but is never null, typ. a tiny array
// boolean isRegistered, protected by key set
// regLock, lock object to prevent duplicate registrations
// boolean isBlocking, protected by regLock
/**
* 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();
//
// sync(keySet) { return isRegistered; }
/**
* 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);
//
// sync(keySet) { return findKey(sel); }
/**
* 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 another invocation of this method or of the {@link
* #configureBlocking(boolean) configureBlocking} method is in progress
* then it will first block until the other operation is complete. This
* method will then synchronize on the selector's key set and therefore may
* block if invoked concurrently with another registration or selection
* operation involving the same selector. </p>
*
* <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;
//
// sync(regLock) {
// sync(keySet) { look for selector }
// if (channel found) { set interest ops -- may block in selector;
// return key; }
// create new key -- may block somewhere in selector;
// sync(keySet) { add key; }
// attach(attachment);
// return key;
// }
/**
* 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.
*
* <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;
//
// sync(regLock) {
// sync(keySet) { throw IBME if block && isRegistered; }
// change 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 {@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();
}