The AbstractSelector.java Java example source code
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* accompanied this code).
*
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package java.nio.channels.spi;
import java.io.IOException;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.util.HashSet;
import java.util.Set;
import sun.nio.ch.Interruptible;
import java.util.concurrent.atomic.AtomicBoolean;
/**
* Base implementation class for selectors.
*
* <p> This class encapsulates the low-level machinery required to implement
* the interruption of selection operations. A concrete selector class must
* invoke the {@link #begin begin} and {@link #end end} methods before and
* after, respectively, invoking an I/O operation that might block
* indefinitely. In order to ensure that the {@link #end end} method is always
* invoked, these methods should be used within a
* <tt>try ... finally block:
*
* <blockquote> * try {
* begin();
* // Perform blocking I/O operation here
* ...
* } finally {
* end();
* }</pre>
*
* <p> 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 {@link #register register} method that is invoked by a
* selectable channel's {@link AbstractSelectableChannel#register register}
* method in order to perform the actual work of registering a channel. </p>
*
*
* @author Mark Reinhold
* @author JSR-51 Expert Group
* @since 1.4
*/
public abstract class AbstractSelector
extends Selector
{
private AtomicBoolean selectorOpen = new AtomicBoolean(true);
// The provider that created this selector
private final SelectorProvider provider;
/**
* Initializes a new instance of this class.
*
* @param provider
* The provider that created this selector
*/
protected AbstractSelector(SelectorProvider provider) {
this.provider = provider;
}
private final Set<SelectionKey> cancelledKeys = new HashSet();
void cancel(SelectionKey k) { // package-private
synchronized (cancelledKeys) {
cancelledKeys.add(k);
}
}
/**
* Closes this selector.
*
* <p> If the selector has already been closed then this method returns
* immediately. Otherwise it marks the selector as closed and then invokes
* the {@link #implCloseSelector implCloseSelector} method in order to
* complete the close operation. </p>
*
* @throws IOException
* If an I/O error occurs
*/
public final void close() throws IOException {
boolean open = selectorOpen.getAndSet(false);
if (!open)
return;
implCloseSelector();
}
/**
* Closes this selector.
*
* <p> This method is invoked by the {@link #close 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.
*
* <p> 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 {@link
* java.nio.channels.Selector#wakeup wakeup} method. </p>
*
* @throws IOException
* If an I/O error occurs while closing the selector
*/
protected abstract void implCloseSelector() throws IOException;
public final boolean isOpen() {
return selectorOpen.get();
}
/**
* Returns the provider that created this channel.
*
* @return The provider that created this channel
*/
public final SelectorProvider provider() {
return provider;
}
/**
* Retrieves this selector's cancelled-key set.
*
* <p> This set should only be used while synchronized upon it.
*
* @return The cancelled-key set
*/
protected final Set<SelectionKey> cancelledKeys() {
return cancelledKeys;
}
/**
* Registers the given channel with this selector.
*
* <p> This method is invoked by a channel's {@link
* AbstractSelectableChannel#register register} method in order to perform
* the actual work of registering the channel with this selector. </p>
*
* @param ch
* The channel to be registered
*
* @param ops
* The initial interest set, which must be valid
*
* @param att
* The initial attachment for the resulting key
*
* @return A new key representing the registration of the given channel
* with this selector
*/
protected abstract SelectionKey register(AbstractSelectableChannel ch,
int ops, Object att);
/**
* Removes the given key from its channel's key set.
*
* <p> This method must be invoked by the selector for each channel that it
* deregisters. </p>
*
* @param key
* The selection key to be removed
*/
protected final void deregister(AbstractSelectionKey key) {
((AbstractSelectableChannel)key.channel()).removeKey(key);
}
// -- Interruption machinery --
private Interruptible interruptor = null;
/**
* Marks the beginning of an I/O operation that might block indefinitely.
*
* <p> This method should be invoked in tandem with the {@link #end end}
* method, using a <tt>try ... finally block as
* shown <a href="#be">above, in order to implement interruption for
* this selector.
*
* <p> Invoking this method arranges for the selector's {@link
* Selector#wakeup wakeup} method to be invoked if a thread's {@link
* Thread#interrupt interrupt} method is invoked while the thread is
* blocked in an I/O operation upon the selector. </p>
*/
protected final void begin() {
if (interruptor == null) {
interruptor = new Interruptible() {
public void interrupt(Thread ignore) {
AbstractSelector.this.wakeup();
}};
}
AbstractInterruptibleChannel.blockedOn(interruptor);
Thread me = Thread.currentThread();
if (me.isInterrupted())
interruptor.interrupt(me);
}
/**
* Marks the end of an I/O operation that might block indefinitely.
*
* <p> This method should be invoked in tandem with the {@link #begin begin}
* method, using a <tt>try ... finally block as
* shown <a href="#be">above, in order to implement interruption for
* this selector. </p>
*/
protected final void end() {
AbstractInterruptibleChannel.blockedOn(null);
}
}
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