Merge branch 'libs/jetty/upstream' into libs/jetty/local

[gigi.git] / lib / jetty / org / eclipse / jetty / util / thread / Sweeper.java

diff --git a/lib/jetty/org/eclipse/jetty/util/thread/Sweeper.java b/lib/jetty/org/eclipse/jetty/util/thread/Sweeper.java
new file mode 100644 (file)
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+++ b/lib/jetty/org/eclipse/jetty/util/thread/Sweeper.java
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+//
+//  ========================================================================
+//  Copyright (c) 1995-2016 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.List;
+import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+
+import org.eclipse.jetty.util.component.AbstractLifeCycle;
+import org.eclipse.jetty.util.log.Log;
+import org.eclipse.jetty.util.log.Logger;
+
+/**
+ * <p>A utility class to perform periodic sweeping of resources.</p>
+ * <p>{@link Sweepable} resources may be added to or removed from a
+ * {@link Sweeper} and the resource implementation decides whether
+ * it should be swept or not.</p>
+ * <p>If a {@link Sweepable} resources is itself a container of
+ * other sweepable resources, it will forward the sweep operation
+ * to children resources, and so on recursively.</p>
+ * <p>Typical usage is to add {@link Sweeper} as a bean to an existing
+ * container:</p>
+ * <pre>
+ * Server server = new Server();
+ * server.addBean(new Sweeper(), true);
+ * server.start();
+ * </pre>
+ * Code that knows it has sweepable resources can then lookup the
+ * {@link Sweeper} and offer the sweepable resources to it:
+ * <pre>
+ * class MyComponent implements Sweeper.Sweepable
+ * {
+ *     private final long creation;
+ *     private volatile destroyed;
+ *
+ *     MyComponent(Server server)
+ *     {
+ *         this.creation = System.nanoTime();
+ *         Sweeper sweeper = server.getBean(Sweeper.class);
+ *         sweeper.offer(this);
+ *     }
+ *
+ *     void destroy()
+ *     {
+ *         destroyed = true;
+ *     }
+ *
+ *     &#64;Override
+ *     public boolean sweep()
+ *     {
+ *         return destroyed;
+ *     }
+ * }
+ * </pre>
+ */
+public class Sweeper extends AbstractLifeCycle implements Runnable
+{
+    private static final Logger LOG = Log.getLogger(Sweeper.class);
+
+    private final AtomicReference<List<Sweepable>> items = new AtomicReference<>();
+    private final AtomicReference<Scheduler.Task> task = new AtomicReference<>();
+    private final Scheduler scheduler;
+    private final long period;
+
+    public Sweeper(Scheduler scheduler, long period)
+    {
+        this.scheduler = scheduler;
+        this.period = period;
+    }
+
+    @Override
+    protected void doStart() throws Exception
+    {
+        super.doStart();
+        items.set(new CopyOnWriteArrayList<Sweepable>());
+        activate();
+    }
+
+    @Override
+    protected void doStop() throws Exception
+    {
+        deactivate();
+        items.set(null);
+        super.doStop();
+    }
+
+    public int getSize()
+    {
+        List<Sweepable> refs = items.get();
+        return refs == null ? 0 : refs.size();
+    }
+
+    public boolean offer(Sweepable sweepable)
+    {
+        List<Sweepable> refs = items.get();
+        if (refs == null)
+            return false;
+        refs.add(sweepable);
+        if (LOG.isDebugEnabled())
+            LOG.debug("Resource offered {}", sweepable);
+        return true;
+    }
+
+    public boolean remove(Sweepable sweepable)
+    {
+        List<Sweepable> refs = items.get();
+        return refs != null && refs.remove(sweepable);
+    }
+
+    @Override
+    public void run()
+    {
+        List<Sweepable> refs = items.get();
+        if (refs == null)
+            return;
+        for (Sweepable sweepable : refs)
+        {
+            try
+            {
+                if (sweepable.sweep())
+                {
+                    refs.remove(sweepable);
+                    if (LOG.isDebugEnabled())
+                        LOG.debug("Resource swept {}", sweepable);
+                }
+            }
+            catch (Throwable x)
+            {
+                LOG.info("Exception while sweeping " + sweepable, x);
+            }
+        }
+        activate();
+    }
+
+    private void activate()
+    {
+        if (isRunning())
+        {
+            Scheduler.Task t = scheduler.schedule(this, period, TimeUnit.MILLISECONDS);
+            if (LOG.isDebugEnabled())
+                LOG.debug("Scheduled in {} ms sweep task {}", period, t);
+            task.set(t);
+        }
+        else
+        {
+            if (LOG.isDebugEnabled())
+                LOG.debug("Skipping sweep task scheduling");
+        }
+    }
+
+    private void deactivate()
+    {
+        Scheduler.Task t = task.getAndSet(null);
+        if (t != null)
+        {
+            boolean cancelled = t.cancel();
+            if (LOG.isDebugEnabled())
+                LOG.debug("Cancelled ({}) sweep task {}", cancelled, t);
+        }
+    }
+
+    /**
+     * <p>A {@link Sweepable} resource implements this interface to
+     * signal to a {@link Sweeper} or to a parent container if it
+     * needs to be swept or not.</p>
+     * <p>Typical implementations will check their own internal state
+     * and return true or false from {@link #sweep()} to indicate
+     * whether they should be swept.</p>
+     */
+    public interface Sweepable
+    {
+        /**
+         * @return whether this resource should be swept
+         */
+        public boolean sweep();
+    }
+}