JDK 11 java.base.jmod - Base Module
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⏎ java/nio/channels/SelectionKey.java
/*
* Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.nio.channels;
import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
/**
* 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.
*/
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.
*
* @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.
*
* @return This key's selector
*/
public abstract Selector selector();
/**
* 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.
*
* <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.
*
* <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.
*
* <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
* {@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
* {@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.
*
* <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.
*
* <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.
*
* <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.
*
* <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.
*
* <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.
*
* <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.
*
* <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.
*
* <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.
*
* <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.
*
* <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.
*
* @return The object currently attached to this key,
* or {@code null} if there is no attachment
*/
public final Object attachment() {
return attachment;
}
}
⏎ java/nio/channels/SelectionKey.java
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