AbstractSelector (Java Platform SE 7 b59)

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Java™ Platform
Standard Ed. 7
DRAFT ea-b59

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java.nio.channels.spi
Class AbstractSelector

java.lang.Object
  java.nio.channels.Selector
      java.nio.channels.spi.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.

Since:: 1.4

Constructor Summary
Modifier Constructor and Description

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

Method Summary
Modifier and Type Method and Description

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

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

void close()
          Closes this selector.

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

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

protected abstract void implCloseSelector()
          Closes this selector.

boolean isOpen()
          Tells whether or not this selector is open.

SelectorProvider provider()
          Returns the provider that created this channel.

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

Methods inherited from class java.nio.channels.Selector

keys, open, select, select, selectedKeys, selectNow, wakeup

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

AbstractSelector

protected AbstractSelector(SelectorProvider provider)

Initializes a new instance of this class.

Method Detail

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 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.