AbstractSelectableChannel (Java SE 26 & JDK 26)
Description: declaration: module: java.base, package: java.nio.channels.spi, class: AbstractSelectableChannel
Keywords: java.nio.channels.spi.AbstractSelectableChannel class

# Class AbstractSelectableChannel

java.lang.Object
java.nio.channels.spi.AbstractInterruptibleChannel
java.nio.channels.SelectableChannel
java.nio.channels.spi.AbstractSelectableChannel

All Implemented Interfaces:
  `Closeable, AutoCloseable, Channel, InterruptibleChannel`

Direct Known Subclasses:
  `DatagramChannel, Pipe.SinkChannel, Pipe.SourceChannel, SctpChannel, SctpMultiChannel, SctpServerChannel, ServerSocketChannel, SocketChannel`

public abstract class AbstractSelectableChannel extends SelectableChannel
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 protected abstract methods defined in this class need not synchronize against other threads that might be engaged in the same operations.

Since:
  1.4

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `AbstractSelectableChannel(SelectorProvider provider)`
  Initializes a new instance of this class.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `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.
  `protected final void`
  `implCloseChannel()`
  Closes this channel.
  `protected abstract void`
  `implCloseSelectableChannel()`
  Closes this selectable channel.
  `protected abstract void`
  `implConfigureBlocking(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.

  ### Methods declared in class SelectableChannel

  `register, validOps`
  Modifier and Type
  Method
  Description
  `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.

  ### Methods declared in class AbstractInterruptibleChannel

  `begin, close, end, isOpen`
  Modifier and Type
  Method
  Description
  `protected final void`
  `begin()`
  Marks the beginning of an I/O operation that might block indefinitely.
  `final void`
  `close()`
  Closes this channel.
  `protected final void`
  `end(boolean completed)`
  Marks the end of an I/O operation that might block indefinitely.
  `final boolean`
  `isOpen()`
  Tells whether or not this channel is open.

  ### Methods declared in class Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`
  Modifier and Type
  Method
  Description
  `protected Object`
  `clone()`
  Creates and returns a copy of this object.
  `boolean`
  `equals(Object obj)`
  Indicates whether some other object is "equal to" this one.
  `protected void`
  `finalize()`
  Deprecated, for removal: This API element is subject to removal in a future version.
  Finalization is deprecated and subject to removal in a future release.
  `final Class<?>`
  `getClass()`
  Returns the runtime class of this `Object`.
  `int`
  `hashCode()`
  Returns a hash code value for this object.
  `final void`
  `notify()`
  Wakes up a single thread that is waiting on this object's monitor.
  `final void`
  `notifyAll()`
  Wakes up all threads that are waiting on this object's monitor.
  `String`
  `toString()`
  Returns a string representation of the object.
  `final void`
  `wait()`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
  `final void`
  `wait(long timeoutMillis)`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
  `final void`
  `wait(long timeoutMillis, int nanos)`
  Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

- ## Constructor Details

  - ### AbstractSelectableChannel

    protected AbstractSelectableChannel(SelectorProvider provider)
    Initializes a new instance of this class.
    Parameters:
      `provider` - The provider that created this channel

- ## Method Details

  - ### provider

    public final SelectorProvider provider()
    Returns the provider that created this channel.
    Specified by:
      `provider` in class `SelectableChannel`
    Returns:
      The provider that created this channel

  - ### isRegistered

    public final boolean isRegistered()
    Description copied from class: `SelectableChannel`
    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.

    Specified by:
      `isRegistered` in class `SelectableChannel`
    Returns:
      `true` if, and only if, this channel is registered

  - ### keyFor

    public final SelectionKey keyFor(Selector sel)
    Description copied from class: `SelectableChannel`
    Retrieves the key representing the channel's registration with the given selector.
    Specified by:
      `keyFor` in class `SelectableChannel`
    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

  - ### register

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

    Specified by:
      `register` in class `SelectableChannel`
    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` - If the selector is closed
      `IllegalBlockingModeException` - If this channel is in blocking mode
      `IllegalSelectorException` - If this channel was not created by the same provider as the given selector
      `CancelledKeyException` - If this channel is currently registered with the given selector but the corresponding key has already been cancelled
      `IllegalArgumentException` - If a bit in the `ops` set does not correspond to an operation that is supported by this channel, that is, if `set & ~validOps() != 0`
      `ClosedChannelException` - If this channel is closed

  - ### implCloseChannel

    protected final void implCloseChannel() throws IOException
    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.

    Specified by:
      `implCloseChannel` in class `AbstractInterruptibleChannel`
    Throws:
      `IOException` - If an I/O error occurs while closing the channel

  - ### implCloseSelectableChannel

    protected abstract void implCloseSelectableChannel() throws IOException
    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

  - ### isBlocking

    public final boolean isBlocking()
    Description copied from class: `SelectableChannel`
    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.

    Specified by:
      `isBlocking` in class `SelectableChannel`
    Returns:
      `true` if, and only if, this channel is in blocking mode

  - ### blockingLock

    public final Object blockingLock()
    Description copied from class: `SelectableChannel`
    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.
    Specified by:
      `blockingLock` in class `SelectableChannel`
    Returns:
      The blocking-mode lock object

  - ### configureBlocking

    public final SelectableChannel configureBlocking(boolean block) throws IOException
    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.

    Specified by:
      `configureBlocking` in class `SelectableChannel`
    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:
      `ClosedChannelException` - If this channel is closed
      `IOException` - If an I/O error occurs

  - ### implConfigureBlocking

    protected abstract void implConfigureBlocking(boolean block) throws IOException
    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