AbstractSelector

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.

Protected Constructor Summary

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

Public Method Summary

final void
close()
Closes this selector.
final boolean
isOpen()
Tells whether or not this selector is open.
final SelectorProvider
provider()
Returns the provider that created this channel.

Protected Method Summary

final void
begin()
Marks the beginning of an I/O operation that might block indefinitely.
final Set<SelectionKey>
cancelledKeys()
Retrieves this selector's cancelled-key set.
final void
deregister(AbstractSelectionKey key)
Removes the given key from its channel's key set.
final void
end()
Marks the end of an I/O operation that might block indefinitely.
abstract void
implCloseSelector()
Closes this selector.
abstract SelectionKey
register(AbstractSelectableChannel ch, int ops, Object att)
Registers the given channel with this selector.

Inherited Method Summary

Protected Constructors

protected AbstractSelector (SelectorProvider provider)

Initializes a new instance of this class.

Parameters
provider

Public Methods

public final void close ()

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.

Throws
IOException If an I/O error occurs

public final boolean isOpen ()

Tells whether or not this selector is open.

Returns
  • true if, and only if, this selector is open

public final SelectorProvider provider ()

Returns the provider that created this channel.

Returns
  • The provider that created this channel

Protected Methods

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.

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

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

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.

protected abstract void implCloseSelector ()

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

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