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/**
Copyright (C) SYSTAP, LLC DBA Blazegraph 2006-2016. All rights reserved.
Contact:
SYSTAP, LLC DBA Blazegraph
2501 Calvert ST NW #106
Washington, DC 20008
[email protected]
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/*
* Created on Oct 7, 2010
*/
package com.bigdata.relation.accesspath;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.concurrent.Future;
import java.util.concurrent.locks.ReentrantLock;
/**
* A factory for skins which may be used to multiplex writes against a shared
* {@link BlockingBuffer} instance. Each skin writes through to the backing
* {@link BlockingBuffer} but may be closed independently of the backing
* {@link BlockingBuffer}. This allows multiple produces to share a single
* {@link BlockingBuffer} as long as they use a subset of the
* {@link IBlockingBuffer} API (they can not set the {@link Future} on the
* objects returned by this factory or obtain its
* {@link IBlockingBuffer#iterator()}, but those operations can be performed
* against the shared {@link IBlockingBuffer}).
*
* @author Bryan Thompson
* @version $Id: MultiplexBlockingBuffer.java 3830 2010-10-20 18:30:25Z
* thompsonbry $
*/
public class MultiplexBlockingBuffer {
/** The delegate. */
private final IBlockingBuffer b;
/** Lock guarding internal state. */
private final ReentrantLock lock = new ReentrantLock();
/** The set of opened buffered which have not yet been closed. */
private final LinkedHashSet> set = new LinkedHashSet>();
/** The #of currently open buffers. */
private int counter = 0;
public MultiplexBlockingBuffer(final IBlockingBuffer b) {
if (b == null)
throw new IllegalArgumentException();
this.b = b;
}
public boolean isOpen() {
return b.isOpen();
}
/**
* Create a new skin for the shared buffer, incrementing the count of the
* #of open skins that buffer. The shared buffer will be closed atomically
* once all open skins have been closed.
*/
public IBlockingBuffer newInstance() {
lock.lock();
try {
if(!isOpen())// ???
throw new BufferClosedException();
final IBlockingBuffer n = new InnerBlockingBuffer();
if (!set.add(n))
throw new AssertionError();
counter++;
return n;
} finally {
lock.unlock();
}
}
public void flushAndCloseAll() {
lock.lock();
try {
final Iterator> itr = set.iterator();
while(itr.hasNext()) {
final IBlockingBuffer n = itr.next();
n.close();
}
assert counter == 0;
b.flush();
b.close();
} finally {
lock.unlock();
}
}
/**
* The {@link IBlockingBuffer} reference provided to the constructor.
*/
public IBlockingBuffer getBackingBuffer() {
return b;
}
/**
* Inner "skin" writes through to the backing buffer shared by all skins.
*
* Note: This inner class does not support several of the
* {@link IBlockingBuffer} methods whose semantics are likely to cause
* problems when interpreted in the light of a skin over a shared buffer.
* The only way these methods could be given clear semantics is if the skin
* were actually a full {@link BlockingBuffer} which was coupled to the
* shared buffer. However, that involves double buffering and double copying
* and I do not think that this is worth it.
*/
private class InnerBlockingBuffer implements IBlockingBuffer {
protected InnerBlockingBuffer() {
}
private boolean innerBufferOpen = true;
public IAsynchronousIterator iterator() {
throw new UnsupportedOperationException();
}
public void setFuture(Future future) {
throw new UnsupportedOperationException();
}
public void abort(final Throwable cause) {
lock.lock();
try {
if (!innerBufferOpen)
throw new BufferClosedException();
b.abort(cause);
} finally {
lock.unlock();
}
}
public void close() {
lock.lock();
try {
if (!innerBufferOpen)
return;
innerBufferOpen = false;
if (!set.remove(this))
throw new AssertionError();
counter--;
if (counter == 0) {
/*
* Note: We flush the backing buffer before we close it in
* case it has anything buffered. This covers the normal,
* which is where the caller has already invoked flush() on
* this skin and should not create any harm otherwise.
*/
b.flush();
b.close();
}
} finally {
lock.unlock();
}
}
public Future getFuture() {
return b.getFuture();
}
public boolean isOpen() {
return innerBufferOpen && b.isOpen();
}
public long flush() {
/*
* Nothing to flush. The target is flushed when the outer class is
* closed.
*/
return 0;
}
public void add(E e) {
if (!innerBufferOpen)
throw new BufferClosedException();
b.add(e);
}
public boolean isEmpty() {
return b.isEmpty();
}
public void reset() {
throw new UnsupportedOperationException();
}
public int size() {
return b.size();
}
}
}