java/11 : java.base/java/nio/channels/SelectionKey.java

SelectionKey
https://openjdk.java.net/
GPLv2 + Classpath Exception
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package java.nio.channels;

import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;

A token representing the registration of a SelectableChannel with a Selector.  A selection key is created each time a channel is registered with a
selector.  A key remains valid until it is cancelled by invoking its cancel method, by closing its channel, or by closing its selector. Cancelling a key does not immediately remove it from its selector; it is instead added to the selector's cancelled-key set for removal during the next selection operation. The validity of a key may be tested by invoking its isValid method. 
 A selection key contains two operation sets represented as
integer values.  Each bit of an operation set denotes a category of
selectable operations that are supported by the key's channel.

   The interest set determines which operation categories will be tested for readiness the next time one of the selector's selection methods is invoked. The interest set is initialized with the value given when the key is created; it may later be changed via the interestOps(int) method. 
   The ready set identifies the operation categories for which
  the key's channel has been detected to be ready by the key's selector.
  The ready set is initialized to zero when the key is created; it may later
  be updated by the selector during a selection operation, but it cannot be
  updated directly. 

 That a selection key's ready set indicates that its channel is ready for
some operation category is a hint, but not a guarantee, that an operation in
such a category may be performed by a thread without causing the thread to
block.  A ready set is most likely to be accurate immediately after the
completion of a selection operation.  It is likely to be made inaccurate by
external events and by I/O operations that are invoked upon the
corresponding channel.
 This class defines all known operation-set bits, but precisely which bits are supported by a given channel depends upon the type of the channel. Each subclass of SelectableChannel defines an validOps() method which returns a set identifying just those operations that are supported by the channel. An attempt to set or test an operation-set bit that is not supported by a key's channel will result in an appropriate run-time exception. 
 It is often necessary to associate some application-specific data with a
selection key, for example an object that represents the state of a
higher-level protocol and handles readiness notifications in order to
implement that protocol.  Selection keys therefore support the
attachment of a single arbitrary object to a key. An object can be attached via the attach method and then later retrieved via the attachment method. 
 Selection keys are safe for use by multiple concurrent threads.  A
selection operation will always use the interest-set value that was current
at the moment that the operation began.  
Author: Mark Reinhold, JSR-51 Expert Group
See Also: SelectableChannel
Selector
Since: 1.4/**
 * A token representing the registration of a {@link SelectableChannel} with a
 * {@link Selector}.
 *
 * <p> A selection key is created each time a channel is registered with a
 * selector.  A key remains valid until it is <i>cancelled</i> by invoking its
 * {@link #cancel cancel} method, by closing its channel, or by closing its
 * selector.  Cancelling a key does not immediately remove it from its
 * selector; it is instead added to the selector's <a
 * href="Selector.html#ks"><i>cancelled-key set</i></a> for removal during the
 * next selection operation.  The validity of a key may be tested by invoking
 * its {@link #isValid isValid} method.
 *
 * <a id="opsets"></a>
 *
 * <p> A selection key contains two <i>operation sets</i> represented as
 * integer values.  Each bit of an operation set denotes a category of
 * selectable operations that are supported by the key's channel.
 *
 * <ul>
 *
 *   <li><p> The <i>interest set</i> determines which operation categories will
 *   be tested for readiness the next time one of the selector's selection
 *   methods is invoked.  The interest set is initialized with the value given
 *   when the key is created; it may later be changed via the {@link
 *   #interestOps(int)} method. </p></li>
 *
 *   <li><p> The <i>ready set</i> identifies the operation categories for which
 *   the key's channel has been detected to be ready by the key's selector.
 *   The ready set is initialized to zero when the key is created; it may later
 *   be updated by the selector during a selection operation, but it cannot be
 *   updated directly. </p></li>
 *
 * </ul>
 *
 * <p> That a selection key's ready set indicates that its channel is ready for
 * some operation category is a hint, but not a guarantee, that an operation in
 * such a category may be performed by a thread without causing the thread to
 * block.  A ready set is most likely to be accurate immediately after the
 * completion of a selection operation.  It is likely to be made inaccurate by
 * external events and by I/O operations that are invoked upon the
 * corresponding channel.
 *
 * <p> This class defines all known operation-set bits, but precisely which
 * bits are supported by a given channel depends upon the type of the channel.
 * Each subclass of {@link SelectableChannel} defines an {@link
 * SelectableChannel#validOps() validOps()} method which returns a set
 * identifying just those operations that are supported by the channel.  An
 * attempt to set or test an operation-set bit that is not supported by a key's
 * channel will result in an appropriate run-time exception.
 *
 * <p> It is often necessary to associate some application-specific data with a
 * selection key, for example an object that represents the state of a
 * higher-level protocol and handles readiness notifications in order to
 * implement that protocol.  Selection keys therefore support the
 * <i>attachment</i> of a single arbitrary object to a key.  An object can be
 * attached via the {@link #attach attach} method and then later retrieved via
 * the {@link #attachment() attachment} method.
 *
 * <p> Selection keys are safe for use by multiple concurrent threads.  A
 * selection operation will always use the interest-set value that was current
 * at the moment that the operation began.  </p>
 *
 *
 * @author Mark Reinhold
 * @author JSR-51 Expert Group
 * @since 1.4
 *
 * @see SelectableChannel
 * @see Selector
 */

public abstract class SelectionKey {

    Constructs an instance of this class.
/**
     * Constructs an instance of this class.
     */
    protected SelectionKey() { }


    // -- Channel and selector operations --

    Returns the channel for which this key was created.  This method will
continue to return the channel even after the key is cancelled.
Returns:  This key's channel/**
     * Returns the channel for which this key was created.  This method will
     * continue to return the channel even after the key is cancelled.
     *
     * @return  This key's channel
     */
    public abstract SelectableChannel channel();

    Returns the selector for which this key was created.  This method will
continue to return the selector even after the key is cancelled.
Returns:  This key's selector/**
     * Returns the selector for which this key was created.  This method will
     * continue to return the selector even after the key is cancelled.
     *
     * @return  This key's selector
     */
    public abstract Selector selector();

    Tells whether or not this key is valid.
 A key is valid upon creation and remains so until it is cancelled,
its channel is closed, or its selector is closed.  
Returns:  true if, and only if, this key is valid/**
     * Tells whether or not this key is valid.
     *
     * <p> A key is valid upon creation and remains so until it is cancelled,
     * its channel is closed, or its selector is closed.  </p>
     *
     * @return  {@code true} if, and only if, this key is valid
     */
    public abstract boolean isValid();

    Requests that the registration of this key's channel with its selector
be cancelled.  Upon return the key will be invalid and will have been
added to its selector's cancelled-key set.  The key will be removed from
all of the selector's key sets during the next selection operation.
 If this key has already been cancelled then invoking this method has
no effect.  Once cancelled, a key remains forever invalid. 
 This method may be invoked at any time.  It synchronizes on the
selector's cancelled-key set, and therefore may block briefly if invoked
concurrently with a cancellation or selection operation involving the
same selector.  
/**
     * Requests that the registration of this key's channel with its selector
     * be cancelled.  Upon return the key will be invalid and will have been
     * added to its selector's cancelled-key set.  The key will be removed from
     * all of the selector's key sets during the next selection operation.
     *
     * <p> If this key has already been cancelled then invoking this method has
     * no effect.  Once cancelled, a key remains forever invalid. </p>
     *
     * <p> This method may be invoked at any time.  It synchronizes on the
     * selector's cancelled-key set, and therefore may block briefly if invoked
     * concurrently with a cancellation or selection operation involving the
     * same selector.  </p>
     */
    public abstract void cancel();


    // -- Operation-set accessors --

    Retrieves this key's interest set.
 It is guaranteed that the returned set will only contain operation
bits that are valid for this key's channel. 
Throws: CancelledKeyException – 
         If this key has been cancelled
Returns:  This key's interest set/**
     * Retrieves this key's interest set.
     *
     * <p> It is guaranteed that the returned set will only contain operation
     * bits that are valid for this key's channel. </p>
     *
     * @return  This key's interest set
     *
     * @throws  CancelledKeyException
     *          If this key has been cancelled
     */
    public abstract int interestOps();

    Sets this key's interest set to the given value.
 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 change to the key's interest set will be seen by the
next selection operation.
Params: ops –  The new interest set
Throws: IllegalArgumentException –  If a bit in the set does not correspond to an operation that is supported by this key's channel, that is, if (ops & ~channel().validOps()) != 0
CancelledKeyException – 
         If this key has been cancelled
Returns:  This selection key/**
     * Sets this key's interest set to the given value.
     *
     * <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 change to the key's interest set will be seen by the
     * next selection operation.
     *
     * @param  ops  The new interest set
     *
     * @return  This selection key
     *
     * @throws  IllegalArgumentException
     *          If a bit in the set does not correspond to an operation that
     *          is supported by this key's channel, that is, if
     *          {@code (ops & ~channel().validOps()) != 0}
     *
     * @throws  CancelledKeyException
     *          If this key has been cancelled
     */
    public abstract SelectionKey interestOps(int ops);

    Atomically sets this key's interest set to the bitwise union ("or") of the existing interest set and the given value. This method is guaranteed to be atomic with respect to other concurrent calls to this method or to interestOpsAnd(int).  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 change to the key's interest set will be seen by the
next selection operation.
Params: ops –  The interest set to apply
Throws: IllegalArgumentException –  If a bit in the set does not correspond to an operation that is supported by this key's channel, that is, if (ops & ~channel().validOps()) != 0
CancelledKeyException – 
         If this key has been cancelled
Implementation Requirements: The default implementation synchronizes on this key and invokes interestOps() and interestOps(int) to retrieve and set this key's interest set.
Returns:  The previous interest set
Since: 11/**
     * Atomically sets this key's interest set to the bitwise union ("or") of
     * the existing interest set and the given value. This method is guaranteed
     * to be atomic with respect to other concurrent calls to this method or to
     * {@link #interestOpsAnd(int)}.
     *
     * <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 change to the key's interest set will be seen by the
     * next selection operation.
     *
     * @implSpec The default implementation synchronizes on this key and invokes
     * {@code interestOps()} and {@code interestOps(int)} to retrieve and set
     * this key's interest set.
     *
     * @param  ops  The interest set to apply
     *
     * @return  The previous interest set
     *
     * @throws  IllegalArgumentException
     *          If a bit in the set does not correspond to an operation that
     *          is supported by this key's channel, that is, if
     *          {@code (ops & ~channel().validOps()) != 0}
     *
     * @throws  CancelledKeyException
     *          If this key has been cancelled
     *
     * @since 11
     */
    public int interestOpsOr(int ops) {
        synchronized (this) {
            int oldVal = interestOps();
            interestOps(oldVal | ops);
            return oldVal;
        }
    }

    Atomically sets this key's interest set to the bitwise intersection ("and") of the existing interest set and the given value. This method is guaranteed to be atomic with respect to other concurrent calls to this method or to interestOpsOr(int).  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 change to the key's interest set will be seen by the
next selection operation.
Params: ops –  The interest set to apply
Throws: CancelledKeyException – 
         If this key has been cancelled
API Note: Unlike the interestOps(int) and interestOpsOr(int) methods, this method does not throw IllegalArgumentException when invoked with bits in the interest set that do not correspond to an operation that is supported by this key's channel. This is to allow operation bits in the interest set to be cleared using bitwise complement values, e.g., interestOpsAnd(~SelectionKey.OP_READ) will remove the OP_READ from the interest set without affecting other bits.
Implementation Requirements: The default implementation synchronizes on this key and invokes interestOps() and interestOps(int) to retrieve and set this key's interest set.
Returns:  The previous interest set
Since: 11/**
     * Atomically sets this key's interest set to the bitwise intersection ("and")
     * of the existing interest set and the given value. This method is guaranteed
     * to be atomic with respect to other concurrent calls to this method or to
     * {@link #interestOpsOr(int)}.
     *
     * <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 change to the key's interest set will be seen by the
     * next selection operation.
     *
     * @apiNote Unlike the {@code interestOps(int)} and {@code interestOpsOr(int)}
     * methods, this method does not throw {@code IllegalArgumentException} when
     * invoked with bits in the interest set that do not correspond to an
     * operation that is supported by this key's channel. This is to allow
     * operation bits in the interest set to be cleared using bitwise complement
     * values, e.g., {@code interestOpsAnd(~SelectionKey.OP_READ)} will remove
     * the {@code OP_READ} from the interest set without affecting other bits.
     *
     * @implSpec The default implementation synchronizes on this key and invokes
     * {@code interestOps()} and {@code interestOps(int)} to retrieve and set
     * this key's interest set.
     *
     * @param  ops  The interest set to apply
     *
     * @return  The previous interest set
     *
     * @throws  CancelledKeyException
     *          If this key has been cancelled
     *
     * @since 11
     */
    public int interestOpsAnd(int ops) {
        synchronized (this) {
            int oldVal = interestOps();
            interestOps(oldVal & ops);
            return oldVal;
        }
    }

    Retrieves this key's ready-operation set.
 It is guaranteed that the returned set will only contain operation
bits that are valid for this key's channel.  
Throws: CancelledKeyException – 
         If this key has been cancelled
Returns:  This key's ready-operation set/**
     * Retrieves this key's ready-operation set.
     *
     * <p> It is guaranteed that the returned set will only contain operation
     * bits that are valid for this key's channel.  </p>
     *
     * @return  This key's ready-operation set
     *
     * @throws  CancelledKeyException
     *          If this key has been cancelled
     */
    public abstract int readyOps();


    // -- Operation bits and bit-testing convenience methods --

    Operation-set bit for read operations.
 Suppose that a selection key's interest set contains OP_READ at the start of a selection operation. If the selector detects that the corresponding channel is ready for reading, has reached end-of-stream, has been remotely shut down for further reading, or has an error pending, then it will add OP_READ to the key's ready-operation set. 
/**
     * Operation-set bit for read operations.
     *
     * <p> Suppose that a selection key's interest set contains
     * {@code OP_READ} at the start of a <a
     * href="Selector.html#selop">selection operation</a>.  If the selector
     * detects that the corresponding channel is ready for reading, has reached
     * end-of-stream, has been remotely shut down for further reading, or has
     * an error pending, then it will add {@code OP_READ} to the key's
     * ready-operation set.  </p>
     */
    public static final int OP_READ = 1 << 0;

    Operation-set bit for write operations.
 Suppose that a selection key's interest set contains OP_WRITE at the start of a selection operation. If the selector detects that the corresponding channel is ready for writing, has been remotely shut down for further writing, or has an error pending, then it will add OP_WRITE to the key's ready set. 
/**
     * Operation-set bit for write operations.
     *
     * <p> Suppose that a selection key's interest set contains
     * {@code OP_WRITE} at the start of a <a
     * href="Selector.html#selop">selection operation</a>.  If the selector
     * detects that the corresponding channel is ready for writing, has been
     * remotely shut down for further writing, or has an error pending, then it
     * will add {@code OP_WRITE} to the key's ready set.  </p>
     */
    public static final int OP_WRITE = 1 << 2;

    Operation-set bit for socket-connect operations.
 Suppose that a selection key's interest set contains OP_CONNECT at the start of a selection operation. If the selector detects that the corresponding socket channel is ready to complete its connection sequence, or has an error pending, then it will add OP_CONNECT to the key's ready set. 
/**
     * Operation-set bit for socket-connect operations.
     *
     * <p> Suppose that a selection key's interest set contains
     * {@code OP_CONNECT} at the start of a <a
     * href="Selector.html#selop">selection operation</a>.  If the selector
     * detects that the corresponding socket channel is ready to complete its
     * connection sequence, or has an error pending, then it will add
     * {@code OP_CONNECT} to the key's ready set.  </p>
     */
    public static final int OP_CONNECT = 1 << 3;

    Operation-set bit for socket-accept operations.
 Suppose that a selection key's interest set contains OP_ACCEPT at the start of a selection operation. If the selector detects that the corresponding server-socket channel is ready to accept another connection, or has an error pending, then it will add OP_ACCEPT to the key's ready set. 
/**
     * Operation-set bit for socket-accept operations.
     *
     * <p> Suppose that a selection key's interest set contains
     * {@code OP_ACCEPT} at the start of a <a
     * href="Selector.html#selop">selection operation</a>.  If the selector
     * detects that the corresponding server-socket channel is ready to accept
     * another connection, or has an error pending, then it will add
     * {@code OP_ACCEPT} to the key's ready set.  </p>
     */
    public static final int OP_ACCEPT = 1 << 4;

    Tests whether this key's channel is ready for reading.
 An invocation of this method of the form k.isReadable() behaves in exactly the same way as the expression 

k.readyOps() & OP_READ != 0

 If this key's channel does not support read operations then this method always returns false. 
Throws: CancelledKeyException – 
         If this key has been cancelled
Returns:  true if, and only if, readyOps() & OP_READ is nonzero/**
     * Tests whether this key's channel is ready for reading.
     *
     * <p> An invocation of this method of the form {@code k.isReadable()}
     * behaves in exactly the same way as the expression
     *
     * <blockquote><pre>{@code
     * k.readyOps() & OP_READ != 0
     * }</pre></blockquote>
     *
     * <p> If this key's channel does not support read operations then this
     * method always returns {@code false}.  </p>
     *
     * @return  {@code true} if, and only if,
                {@code readyOps() & OP_READ} is nonzero
     *
     * @throws  CancelledKeyException
     *          If this key has been cancelled
     */
    public final boolean isReadable() {
        return (readyOps() & OP_READ) != 0;
    }

    Tests whether this key's channel is ready for writing.
 An invocation of this method of the form k.isWritable() behaves in exactly the same way as the expression 

k.readyOps() & OP_WRITE != 0

 If this key's channel does not support write operations then this method always returns false. 
Throws: CancelledKeyException – 
         If this key has been cancelled
Returns:  true if, and only if, readyOps() & OP_WRITE is nonzero/**
     * Tests whether this key's channel is ready for writing.
     *
     * <p> An invocation of this method of the form {@code k.isWritable()}
     * behaves in exactly the same way as the expression
     *
     * <blockquote><pre>{@code
     * k.readyOps() & OP_WRITE != 0
     * }</pre></blockquote>
     *
     * <p> If this key's channel does not support write operations then this
     * method always returns {@code false}.  </p>
     *
     * @return  {@code true} if, and only if,
     *          {@code readyOps() & OP_WRITE} is nonzero
     *
     * @throws  CancelledKeyException
     *          If this key has been cancelled
     */
    public final boolean isWritable() {
        return (readyOps() & OP_WRITE) != 0;
    }

    Tests whether this key's channel has either finished, or failed to
finish, its socket-connection operation.
 An invocation of this method of the form k.isConnectable() behaves in exactly the same way as the expression 

k.readyOps() & OP_CONNECT != 0

 If this key's channel does not support socket-connect operations then this method always returns false. 
Throws: CancelledKeyException – 
         If this key has been cancelled
Returns:  true if, and only if, readyOps() & OP_CONNECT is nonzero/**
     * Tests whether this key's channel has either finished, or failed to
     * finish, its socket-connection operation.
     *
     * <p> An invocation of this method of the form {@code k.isConnectable()}
     * behaves in exactly the same way as the expression
     *
     * <blockquote><pre>{@code
     * k.readyOps() & OP_CONNECT != 0
     * }</pre></blockquote>
     *
     * <p> If this key's channel does not support socket-connect operations
     * then this method always returns {@code false}.  </p>
     *
     * @return  {@code true} if, and only if,
     *          {@code readyOps() & OP_CONNECT} is nonzero
     *
     * @throws  CancelledKeyException
     *          If this key has been cancelled
     */
    public final boolean isConnectable() {
        return (readyOps() & OP_CONNECT) != 0;
    }

    Tests whether this key's channel is ready to accept a new socket
connection.
 An invocation of this method of the form k.isAcceptable() behaves in exactly the same way as the expression 

k.readyOps() & OP_ACCEPT != 0

 If this key's channel does not support socket-accept operations then this method always returns false. 
Throws: CancelledKeyException – 
         If this key has been cancelled
Returns:  true if, and only if, readyOps() & OP_ACCEPT is nonzero/**
     * Tests whether this key's channel is ready to accept a new socket
     * connection.
     *
     * <p> An invocation of this method of the form {@code k.isAcceptable()}
     * behaves in exactly the same way as the expression
     *
     * <blockquote><pre>{@code
     * k.readyOps() & OP_ACCEPT != 0
     * }</pre></blockquote>
     *
     * <p> If this key's channel does not support socket-accept operations then
     * this method always returns {@code false}.  </p>
     *
     * @return  {@code true} if, and only if,
     *          {@code readyOps() & OP_ACCEPT} is nonzero
     *
     * @throws  CancelledKeyException
     *          If this key has been cancelled
     */
    public final boolean isAcceptable() {
        return (readyOps() & OP_ACCEPT) != 0;
    }


    // -- Attachments --

    private volatile Object attachment;

    private static final AtomicReferenceFieldUpdater<SelectionKey,Object>
        attachmentUpdater = AtomicReferenceFieldUpdater.newUpdater(
            SelectionKey.class, Object.class, "attachment"
        );

    Attaches the given object to this key.
 An attached object may later be retrieved via the 
attachment method. Only one object may be attached at a time; invoking this method causes any previous attachment to be discarded. The current attachment may be discarded by attaching null. 
Params: ob –  The object to be attached; may be null
Returns:  The previously-attached object, if any, otherwise null/**
     * Attaches the given object to this key.
     *
     * <p> An attached object may later be retrieved via the {@link #attachment()
     * attachment} method.  Only one object may be attached at a time; invoking
     * this method causes any previous attachment to be discarded.  The current
     * attachment may be discarded by attaching {@code null}.  </p>
     *
     * @param  ob
     *         The object to be attached; may be {@code null}
     *
     * @return  The previously-attached object, if any,
     *          otherwise {@code null}
     */
    public final Object attach(Object ob) {
        return attachmentUpdater.getAndSet(this, ob);
    }

    Retrieves the current attachment.
Returns:  The object currently attached to this key, or null if there is no attachment/**
     * Retrieves the current attachment.
     *
     * @return  The object currently attached to this key,
     *          or {@code null} if there is no attachment
     */
    public final Object attachment() {
        return attachment;
    }

}
Author:	Mark Reinhold, JSR-51 Expert Group
See Also:	SelectableChannel Selector
Since:	1.4
Throws:	CancelledKeyException – If this key has been cancelled
Returns:	This key's interest set
Params:	ops – The new interest set
Throws:	IllegalArgumentException – If a bit in the set does not correspond to an operation that is supported by this key's channel, that is, if `(ops & ~channel().validOps()) != 0` CancelledKeyException – If this key has been cancelled
Returns:	This selection key
Params:	ops – The interest set to apply
Throws:	IllegalArgumentException – If a bit in the set does not correspond to an operation that is supported by this key's channel, that is, if `(ops & ~channel().validOps()) != 0` CancelledKeyException – If this key has been cancelled
Implementation Requirements:	The default implementation synchronizes on this key and invokes `interestOps()` and `interestOps(int)` to retrieve and set this key's interest set.
Returns:	The previous interest set
Since:	11
Params:	ob – The object to be attached; may be `null`
Returns:	The previously-attached object, if any, otherwise `null`
/

java/ 11/ java.base/java/nio/channels/SelectionKey.java
