AbstractSelectableChannel

AI-generated Key Takeaways

• AbstractSelectableChannel provides a base implementation for selectable channels in Java NIO, handling registration, deregistration, and closing mechanics.

• It manages the channel's blocking mode and selection keys, ensuring thread safety for these operations.

• Concrete channel implementations like SocketChannel and ServerSocketChannel extend this class to provide specific functionalities.

• Subclasses are responsible for implementing implCloseSelectableChannel and implConfigureBlocking methods to handle channel-specific closing and blocking behavior.

public abstract class AbstractSelectableChannel extends SelectableChannel

Known Direct Subclasses DatagramChannel, Pipe.SinkChannel, Pipe.SourceChannel, ServerSocketChannel, SocketChannel DatagramChannel A selectable channel for datagram-oriented sockets.  Pipe.SinkChannel A channel representing the writable end of a Pipe.  Pipe.SourceChannel A channel representing the readable end of a Pipe.  ServerSocketChannel A selectable channel for stream-oriented listening sockets.  SocketChannel A selectable channel for stream-oriented connecting sockets.

Base implementation class for selectable channels.

This class defines methods that handle the mechanics of channel registration, deregistration, and closing. It maintains the current blocking mode of this channel as well as its current set of selection keys. It performs all of the synchronization required to implement the SelectableChannel specification. Implementations of the abstract protected methods defined in this class need not synchronize against other threads that might be engaged in the same operations.

Protected Constructor Summary

AbstractSelectableChannel(SelectorProvider provider) Initializes a new instance of this class.

Public Method Summary

final Object	blockingLock() Retrieves the object upon which the configureBlocking and register methods synchronize.
final SelectableChannel	configureBlocking(boolean block) Adjusts this channel's blocking mode.
final boolean	isBlocking() Tells whether or not every I/O operation on this channel will block until it completes.
final boolean	isRegistered() Tells whether or not this channel is currently registered with any selectors.
final SelectionKey	keyFor(Selector sel) Retrieves the key representing the channel's registration with the given selector.
final SelectorProvider	provider() Returns the provider that created this channel.
final SelectionKey	register(Selector sel, int ops, Object att) Registers this channel with the given selector, returning a selection key.

Protected Method Summary

final void	implCloseChannel() Closes this channel.
abstract void	implCloseSelectableChannel() Closes this selectable channel.
abstract void	implConfigureBlocking(boolean block) Adjusts this channel's blocking mode.

Inherited Method Summary

From class java.nio.channels.SelectableChannel

abstract Object	blockingLock() Retrieves the object upon which the configureBlocking and register methods synchronize.
abstract SelectableChannel	configureBlocking(boolean block) Adjusts this channel's blocking mode.
abstract boolean	isBlocking() Tells whether or not every I/O operation on this channel will block until it completes.
abstract boolean	isRegistered() Tells whether or not this channel is currently registered with any selectors.
abstract SelectionKey	keyFor(Selector sel) Retrieves the key representing the channel's registration with the given selector.
abstract SelectorProvider	provider() Returns the provider that created this channel.
abstract SelectionKey	register(Selector sel, int ops, Object att) Registers this channel with the given selector, returning a selection key.
final SelectionKey	register(Selector sel, int ops) Registers this channel with the given selector, returning a selection key.
abstract int	validOps() Returns an operation set identifying this channel's supported operations.

From class java.nio.channels.spi.AbstractInterruptibleChannel

final void	begin() Marks the beginning of an I/O operation that might block indefinitely.
final void	close() Closes this channel.
final void	end(boolean completed) Marks the end of an I/O operation that might block indefinitely.
abstract void	implCloseChannel() Closes this channel.
final boolean	isOpen() Tells whether or not this channel is open.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

From interface java.nio.channels.Channel

abstract void	close() Closes this channel.
abstract boolean	isOpen() Tells whether or not this channel is open.

From interface java.nio.channels.InterruptibleChannel

abstract void

close() Closes this channel.

From interface java.io.Closeable

abstract void

close() Closes this stream and releases any system resources associated with it.

From interface java.lang.AutoCloseable

abstract void

close() Closes this resource, relinquishing any underlying resources.

Protected Constructors

protected AbstractSelectableChannel (SelectorProvider provider)

Initializes a new instance of this class.

Parameters

provider	The provider that created this channel

Public Methods

public final Object blockingLock ()

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

public final SelectableChannel configureBlocking (boolean block)

Adjusts this channel's blocking mode.

If the given blocking mode is different from the current blocking mode then this method invokes the implConfigureBlocking method, while holding the appropriate locks, in order to change the mode.

Parameters

block	If true then this channel will be placed in blocking mode; if false then it will be placed non-blocking mode

Returns

• This selectable channel

Throws

IOException

public final boolean isBlocking ()

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

public final boolean isRegistered ()

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

public final SelectionKey keyFor (Selector sel)

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

Parameters

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

public final SelectorProvider provider ()

Returns the provider that created this channel.

Returns

• The provider that created this channel

public final SelectionKey register (Selector sel, int ops, Object att)

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

This method first verifies that this channel is open and that the given initial interest set is valid.

If this channel is already registered with the given selector then the selection key representing that registration is returned after setting its interest set to the given value.

Otherwise this channel has not yet been registered with the given selector, so the register method of the selector is invoked while holding the appropriate locks. The resulting key is added to this channel's key set before being returned.

Parameters

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

Returns

• A key representing the registration of this channel with the given selector

Throws

ClosedSelectorException
IllegalBlockingModeException
IllegalSelectorException
CancelledKeyException
IllegalArgumentException
ClosedChannelException

Protected Methods

protected final void implCloseChannel ()

Closes this channel.

This method, which is specified in the AbstractInterruptibleChannel class and is invoked by the close method, in turn invokes the implCloseSelectableChannel method in order to perform the actual work of closing this channel. It then cancels all of this channel's keys.

Throws

IOException

protected abstract void implCloseSelectableChannel ()

Closes this selectable channel.

This method is invoked by the close method in order to perform the actual work of closing the channel. This method is only invoked if the channel has not yet been closed, and it is never invoked more than once.

An implementation of this method must arrange for any other thread that is blocked in an I/O operation upon this channel to return immediately, either by throwing an exception or by returning normally.

Throws

IOException	If an I/O error occurs

protected abstract void implConfigureBlocking (boolean block)

Adjusts this channel's blocking mode.

This method is invoked by the configureBlocking method in order to perform the actual work of changing the blocking mode. This method is only invoked if the new mode is different from the current mode.

Parameters

block	If true then this channel will be placed in blocking mode; if false then it will be placed non-blocking mode

Throws

IOException	If an I/O error occurs