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jetty-9 improved comments

This commit is contained in:
Greg Wilkins 2012-08-31 17:53:18 +10:00
parent 8331b1db71
commit fd5776cf86
3 changed files with 84 additions and 37 deletions
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69
jetty-util/src/main/java/org/eclipse/jetty/util/thread/ConcurrentScheduler.java
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@ -1,3 +1,21 @@
//
// ========================================================================
// Copyright (c) 1995-2012 Mort Bay Consulting Pty. Ltd.
// ------------------------------------------------------------------------
// All rights reserved. This program and the accompanying materials
// are made available under the terms of the Eclipse Public License v1.0
// and Apache License v2.0 which accompanies this distribution.
//
// The Eclipse Public License is available at
// http://www.eclipse.org/legal/epl-v10.html
//
// The Apache License v2.0 is available at
// http://www.opensource.org/licenses/apache2.0.php
//
// You may elect to redistribute this code under either of these licenses.
// ========================================================================
//
package org.eclipse.jetty.util.thread;
import java.nio.channels.IllegalSelectorException;
@ -15,7 +33,7 @@ import org.eclipse.jetty.util.log.Logger;
/*------------------------------------------------------------ */
/**
* This is an experimental no-lock scheduler.
* It is optimized on the assumption that most timers either get cancelled quickly or last to expiry, thus
* It is optimised on the assumption that most timers either get cancelled quickly or last to expiry, thus
* events are initially queued in a constant time queue implemented with a no-lock FIFO. Events
* that are likely to be cancelled quickly will be removed from the delay list when they are cancelled.
* The events that survive the delay list are then queued for executiong using a ConcurrentSkipListSet to
@ -43,7 +61,7 @@ public class ConcurrentScheduler extends AggregateLifeCycle implements Runnable,
public ConcurrentScheduler(Executor executor)
{
this(executor,5000);
this(executor,8192);
}
public ConcurrentScheduler(Executor executor,int delayQms)
@ -263,9 +281,22 @@ public class ConcurrentScheduler extends AggregateLifeCycle implements Runnable,
/* ------------------------------------------------------------ */
/**
* A no lock FIFO queue used to provide a fixed delay for the handling
* of scheduled events.
*/
private static class Queue
{
/*
* Roughly based on public domain lock free queue algorithm from:
* http://www.java2s.com/Code/Java/Collections-Data-Structure/ConcurrentDoublyLinkedList.htm
*
* Importantly this implementation supports pro active removal of nodes when cancel is called.
* It does not use deletion markers as the intention is to allow the node to be rapidly garbage collected.
*/
final int _delay;
final QNode _head = new QNode(null,0,null,null);
final QNode _tail = new QNode(null,0,null,null);
@ -338,36 +369,7 @@ public class ConcurrentScheduler extends AggregateLifeCycle implements Runnable,
* http://www.java2s.com/Code/Java/Collections-Data-Structure/ConcurrentDoublyLinkedList.htm
*/
private static class QNode
{
/* These are invarients
*
* (1) next references are the ground truth.
*
* (2) next references to dead nodes can be improved by
* swinging them further forward around the dead node.
*
* (2.1) next references are still correct when pointing to dead nodes
* and next references from dead nodes are left as they were when the node
* was deleted.
*
* (2.2) multiple dead nodes may point forward to the same node.
*
* (3) backward pointers were correct when they were installed.
*
* (3.1) backward pointers are correct when pointing to any node which
* next reference points to them, but since more than one next reference
* may point to them, the live one is best.
*
* (4) backward pointers that are out of date due to deletion
* point to a deleted node, and need to point further back until they point
* to the live node that points to their source.
*
* (5) backward pointers from a dead node cannot be "improved" since there may be no live node pointing
* forward to their origin. (However, it does no harm to try to improve them
* while racing with a deletion.)
*
*/
{
final Event _event;
final long _dequeueAt;
final AtomicReference<QNode> _next=new AtomicReference<>();
@ -380,7 +382,6 @@ public class ConcurrentScheduler extends AggregateLifeCycle implements Runnable,
_prev=prev;
_next.set(next);
}
/**
* Returns the previous non-deleted event, patching up pointers as needed.

18
jetty-util/src/main/java/org/eclipse/jetty/util/thread/SimpleScheduler.java
View File

@ -1,3 +1,21 @@
//
// ========================================================================
// Copyright (c) 1995-2012 Mort Bay Consulting Pty. Ltd.
// ------------------------------------------------------------------------
// All rights reserved. This program and the accompanying materials
// are made available under the terms of the Eclipse Public License v1.0
// and Apache License v2.0 which accompanies this distribution.
//
// The Eclipse Public License is available at
// http://www.eclipse.org/legal/epl-v10.html
//
// The Apache License v2.0 is available at
// http://www.opensource.org/licenses/apache2.0.php
//
// You may elect to redistribute this code under either of these licenses.
// ========================================================================
//
package org.eclipse.jetty.util.thread;
import java.util.Timer;

34
jetty-util/src/test/java/org/eclipse/jetty/util/thread/SchedulerTest.java
View File

@ -1,8 +1,27 @@
//
// ========================================================================
// Copyright (c) 1995-2012 Mort Bay Consulting Pty. Ltd.
// ------------------------------------------------------------------------
// All rights reserved. This program and the accompanying materials
// are made available under the terms of the Eclipse Public License v1.0
// and Apache License v2.0 which accompanies this distribution.
//
// The Eclipse Public License is available at
// http://www.eclipse.org/legal/epl-v10.html
//
// The Apache License v2.0 is available at
// http://www.opensource.org/licenses/apache2.0.php
//
// You may elect to redistribute this code under either of these licenses.
// ========================================================================
//
package org.eclipse.jetty.util.thread;
import java.util.Arrays;
import java.util.Collection;
import java.util.Random;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
@ -22,12 +41,15 @@ import org.junit.runners.Parameterized;
@RunWith(value = Parameterized.class)
public class SchedulerTest
{
public static Executor executor = Executors.newFixedThreadPool(256);
@Parameterized.Parameters
public static Collection<Object[]> data()
{
Object[][] data = new Object[][]{
{new SimpleScheduler()},
{new ConcurrentScheduler(Executors.newCachedThreadPool(),2000)}
{new SimpleScheduler()},
{new ConcurrentScheduler(executor,0)},
{new ConcurrentScheduler(executor,2000)}
};
return Arrays.asList(data);
}
@ -141,9 +163,11 @@ public class SchedulerTest
final int delay=random.nextInt((int)(end-now));
final long expected = now+delay;
int cancel=random.nextInt(50);
int cancel=random.nextInt(100);
if (cancel==0)
cancel=(int)(end-now)+1000;
else
cancel=cancel/4;
schedules.incrementAndGet();
Scheduler.Task task=_scheduler.schedule(new Runnable()
@ -180,6 +204,10 @@ public class SchedulerTest
for (Thread thread : test)
thread.join();
//System.err.println(schedules);
//System.err.println(executions);
//System.err.println(cancellations);
// there were some executions and cancellations
Assert.assertThat(executions.getCount(),Matchers.greaterThan(0L));