Module java.base
Package java.nio.channels.spi

Class AbstractSelector

java.lang.Object
java.nio.channels.Selector
java.nio.channels.spi.AbstractSelector
All Implemented Interfaces:
Closeable, AutoCloseable
public abstract class AbstractSelector extends Selector
Base implementation class for selectors.

This class encapsulates the low-level machinery required to implement the interruption of selection operations. A concrete selector class must invoke the begin and end methods before and after, respectively, invoking an I/O operation that might block indefinitely. In order to ensure that the end method is always invoked, these methods should be used within a try ... finally block: 

 try {
     begin();
     // Perform blocking I/O operation here
     ...
 } finally {
     end();
 }

This class also defines methods for maintaining a selector's cancelled-key set and for removing a key from its channel's key set, and declares the abstract register method that is invoked by a selectable channel's register method in order to perform the actual work of registering a channel.

Since:
1.4

  • Constructor Details

    • AbstractSelector

      protected AbstractSelector​(SelectorProvider provider)
      Initializes a new instance of this class.
      Parameters:
      provider - The provider that created this selector

  • Method Details

    • close

      public final void close() throws IOException
      Closes this selector.

      If the selector has already been closed then this method returns immediately. Otherwise it marks the selector as closed and then invokes the implCloseSelector method in order to complete the close operation.

      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Specified by:
      close in class Selector
      Throws:
      IOException - If an I/O error occurs

    • implCloseSelector

      protected abstract void implCloseSelector() throws IOException
      Closes this selector.

      This method is invoked by the close method in order to perform the actual work of closing the selector. This method is only invoked if the selector 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 a selection operation upon this selector to return immediately as if by invoking the wakeup method.

      Throws:
      IOException - If an I/O error occurs while closing the selector

    • isOpen

      public final boolean isOpen()
      Description copied from class: Selector
      Tells whether or not this selector is open.
      Specified by:
      isOpen in class Selector
      Returns:
      true if, and only if, this selector is open

    • provider

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

    • cancelledKeys

      protected final Set<SelectionKey> cancelledKeys()
      Retrieves this selector's cancelled-key set.

      This set should only be used while synchronized upon it.

      Returns:
      The cancelled-key set

    • register

      protected abstract SelectionKey register​(AbstractSelectableChannel ch, int ops, Object att)
      Registers the given channel with this selector.

      This method is invoked by a channel's register method in order to perform the actual work of registering the channel with this selector.

      Parameters:
      ch - The channel to be registered
      ops - The initial interest set, which must be valid
      att - The initial attachment for the resulting key
      Returns:
      A new key representing the registration of the given channel with this selector

    • deregister

      protected final void deregister​(AbstractSelectionKey key)
      Removes the given key from its channel's key set.

      This method must be invoked by the selector for each channel that it deregisters.

      Parameters:
      key - The selection key to be removed

    • begin

      protected final void begin()
      Marks the beginning of an I/O operation that might block indefinitely.

      This method should be invoked in tandem with the end method, using a try ... finally block as shown above, in order to implement interruption for this selector.

      Invoking this method arranges for the selector's wakeup method to be invoked if a thread's interrupt method is invoked while the thread is blocked in an I/O operation upon the selector.

    • end

      protected final void end()
      Marks the end of an I/O operation that might block indefinitely.

      This method should be invoked in tandem with the begin method, using a try ... finally block as shown above, in order to implement interruption for this selector.