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*
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* accompanied this code).
*
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package java.nio.channels.spi;
import java.io.IOException;
import java.nio.channels.*;
/**
* Base implementation class for selectable channels.
*
* <p> 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 {@link
* java.nio.channels.SelectableChannel} specification. Implementations of the
* abstract protected methods defined in this class need not synchronize
* against other threads that might be engaged in the same operations. </p>
*
*
* @author Mark Reinhold
* @author Mike McCloskey
* @author JSR-51 Expert Group
* @since 1.4
*/
public abstract class AbstractSelectableChannel
extends SelectableChannel
{
// The provider that created this channel
private final SelectorProvider provider;
// Keys that have been created by registering this channel with selectors.
// They are saved because if this channel is closed the keys must be
// deregistered. Protected by keyLock.
//
private SelectionKey[] keys = null;
private int keyCount = 0;
// Lock for key set and count
private final Object keyLock = new Object();
// Lock for registration and configureBlocking operations
private final Object regLock = new Object();
// Blocking mode, protected by regLock
boolean blocking = true;
/**
* Initializes a new instance of this class.
*/
protected AbstractSelectableChannel(SelectorProvider provider) {
this.provider = provider;
}
/**
* Returns the provider that created this channel.
*
* @return The provider that created this channel
*/
public final SelectorProvider provider() {
return provider;
}
// -- Utility methods for the key set --
private void addKey(SelectionKey k) {
synchronized (keyLock) {
int i = 0;
if ((keys != null) && (keyCount < keys.length)) {
// Find empty element of key array
for (i = 0; i < keys.length; i++)
if (keys[i] == null)
break;
} else if (keys == null) {
keys = new SelectionKey[3];
} else {
// Grow key array
int n = keys.length * 2;
SelectionKey[] ks = new SelectionKey[n];
for (i = 0; i < keys.length; i++)
ks[i] = keys[i];
keys = ks;
i = keyCount;
}
keys[i] = k;
keyCount++;
}
}
private SelectionKey findKey(Selector sel) {
synchronized (keyLock) {
if (keys == null)
return null;
for (int i = 0; i < keys.length; i++)
if ((keys[i] != null) && (keys[i].selector() == sel))
return keys[i];
return null;
}
}
void removeKey(SelectionKey k) { // package-private
synchronized (keyLock) {
for (int i = 0; i < keys.length; i++)
if (keys[i] == k) {
keys[i] = null;
keyCount--;
}
((AbstractSelectionKey)k).invalidate();
}
}
private boolean haveValidKeys() {
synchronized (keyLock) {
if (keyCount == 0)
return false;
for (int i = 0; i < keys.length; i++) {
if ((keys[i] != null) && keys[i].isValid())
return true;
}
return false;
}
}
// -- Registration --
public final boolean isRegistered() {
synchronized (keyLock) {
return keyCount != 0;
}
}
public final SelectionKey keyFor(Selector sel) {
return findKey(sel);
}
/**
* Registers this channel with the given selector, returning a selection key.
*
* <p> This method first verifies that this channel is open and that the
* given initial interest set is valid.
*
* <p> 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.
*
* <p> Otherwise this channel has not yet been registered with the given
* selector, so the {@link AbstractSelector#register 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.
* </p>
*/
public final SelectionKey register(Selector sel, int ops,
Object att)
throws ClosedChannelException
{
if (!isOpen())
throw new ClosedChannelException();
if ((ops & ~validOps()) != 0)
throw new IllegalArgumentException();
synchronized (regLock) {
if (blocking)
throw new IllegalBlockingModeException();
SelectionKey k = findKey(sel);
if (k != null) {
k.interestOps(ops);
k.attach(att);
}
if (k == null) {
// New registration
k = ((AbstractSelector)sel).register(this, ops, att);
addKey(k);
}
return k;
}
}
// -- Closing --
/**
* Closes this channel.
*
* <p> This method, which is specified in the {@link
* AbstractInterruptibleChannel} class and is invoked by the {@link
* java.nio.channels.Channel#close close} method, in turn invokes the
* {@link #implCloseSelectableChannel implCloseSelectableChannel} method in
* order to perform the actual work of closing this channel. It then
* cancels all of this channel's keys. </p>
*/
protected final void implCloseChannel() throws IOException {
implCloseSelectableChannel();
synchronized (keyLock) {
int count = (keys == null) ? 0 : keys.length;
for (int i = 0; i < count; i++) {
SelectionKey k = keys[i];
if (k != null)
k.cancel();
}
}
}
/**
* Closes this selectable channel.
*
* <p> This method is invoked by the {@link java.nio.channels.Channel#close
* 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.
*
* <p> 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.
* </p>
*/
protected abstract void implCloseSelectableChannel() throws IOException;
// -- Blocking --
public final boolean isBlocking() {
synchronized (regLock) {
return blocking;
}
}
public final Object blockingLock() {
return regLock;
}
/**
* Adjusts this channel's blocking mode.
*
* <p> If the given blocking mode is different from the current blocking
* mode then this method invokes the {@link #implConfigureBlocking
* implConfigureBlocking} method, while holding the appropriate locks, in
* order to change the mode. </p>
*/
public final SelectableChannel configureBlocking(boolean block)
throws IOException
{
if (!isOpen())
throw new ClosedChannelException();
synchronized (regLock) {
if (blocking == block)
return this;
if (block && haveValidKeys())
throw new IllegalBlockingModeException();
implConfigureBlocking(block);
blocking = block;
}
return this;
}
/**
* Adjusts this channel's blocking mode.
*
* <p> This method is invoked by the {@link #configureBlocking
* 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. </p>
*
* @throws IOException
* If an I/O error occurs
*/
protected abstract void implConfigureBlocking(boolean block)
throws IOException;
}