Issue #2131 - Introduce a monitored thread pool. (#2260)

* Issue #2131 - Introduce a monitored thread pool.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

* Issue #2131 - Introduce a monitored thread pool.

Updated to use SampleStatistic and CounterStatistics.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

* Issue #2131 - Introduce a monitored thread pool.

Adding statistics fields as beans.

Signed-off-by: Simone Bordet <simone.bordet@gmail.com>

jetty-util/src/main/java/org/eclipse/jetty/util/thread/MonitoredQueuedThreadPool.java

@@ -0,0 +1,162 @@
+//
+//  ========================================================================
+//  Copyright (c) 1995-2018 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 org.eclipse.jetty.util.BlockingArrayQueue;
+import org.eclipse.jetty.util.annotation.ManagedAttribute;
+import org.eclipse.jetty.util.annotation.ManagedObject;
+import org.eclipse.jetty.util.annotation.ManagedOperation;
+import org.eclipse.jetty.util.statistic.CounterStatistic;
+import org.eclipse.jetty.util.statistic.SampleStatistic;
+
+/**
+ * <p>A {@link QueuedThreadPool} subclass that monitors its own activity by recording queue and task statistics.</p>
+ */
+@ManagedObject
+public class MonitoredQueuedThreadPool extends QueuedThreadPool
+{
+    private final CounterStatistic queueStats = new CounterStatistic();
+    private final SampleStatistic queueLatencyStats = new SampleStatistic();
+    private final SampleStatistic taskLatencyStats = new SampleStatistic();
+    private final CounterStatistic threadStats = new CounterStatistic();
+
+    public MonitoredQueuedThreadPool()
+    {
+        this(256);
+    }
+
+    public MonitoredQueuedThreadPool(int maxThreads)
+    {
+        super(maxThreads, maxThreads, 24 * 3600 * 1000, new BlockingArrayQueue<>(maxThreads, 256));
+        addBean(queueStats);
+        addBean(queueLatencyStats);
+        addBean(taskLatencyStats);
+        addBean(threadStats);
+    }
+
+    @Override
+    public void execute(final Runnable job)
+    {
+        queueStats.increment();
+        long begin = System.nanoTime();
+        super.execute(new Runnable()
+        {
+            @Override
+            public void run()
+            {
+                long queueLatency = System.nanoTime() - begin;
+                queueStats.decrement();
+                threadStats.increment();
+                queueLatencyStats.set(queueLatency);
+                long start = System.nanoTime();
+                try
+                {
+                    job.run();
+                }
+                finally
+                {
+                    long taskLatency = System.nanoTime() - start;
+                    threadStats.decrement();
+                    taskLatencyStats.set(taskLatency);
+                }
+            }
+
+            @Override
+            public String toString()
+            {
+                return job.toString();
+            }
+        });
+    }
+
+    /**
+     * Resets the statistics.
+     */
+    @ManagedOperation(value = "resets the statistics", impact = "ACTION")
+    public void reset()
+    {
+        queueStats.reset();
+        queueLatencyStats.reset();
+        taskLatencyStats.reset();
+        threadStats.reset(0);
+    }
+
+    /**
+     * @return the number of tasks executed
+     */
+    @ManagedAttribute("the number of tasks executed")
+    public long getTasks()
+    {
+        return taskLatencyStats.getTotal();
+    }
+
+    /**
+     * @return the maximum number of busy threads
+     */
+    @ManagedAttribute("the maximum number of busy threads")
+    public int getMaxBusyThreads()
+    {
+        return (int)threadStats.getMax();
+    }
+
+    /**
+     * @return the maximum task queue size
+     */
+    @ManagedAttribute("the maximum task queue size")
+    public int getMaxQueueSize()
+    {
+        return (int)queueStats.getMax();
+    }
+
+    /**
+     * @return the average time a task remains in the queue, in nanoseconds
+     */
+    @ManagedAttribute("the average time a task remains in the queue, in nanoseconds")
+    public long getAverageQueueLatency()
+    {
+        return (long)queueLatencyStats.getMean();
+    }
+
+    /**
+     * @return the maximum time a task remains in the queue, in nanoseconds
+     */
+    @ManagedAttribute("the maximum time a task remains in the queue, in nanoseconds")
+    public long getMaxQueueLatency()
+    {
+        return queueLatencyStats.getMax();
+    }
+
+    /**
+     * @return the average task execution time, in nanoseconds
+     */
+    @ManagedAttribute("the average task execution time, in nanoseconds")
+    public long getAverageTaskLatency()
+    {
+        return (long)taskLatencyStats.getMean();
+    }
+
+    /**
+     * @return the maximum task execution time, in nanoseconds
+     */
+    @ManagedAttribute("the maximum task execution time, in nanoseconds")
+    public long getMaxTaskLatency()
+    {
+        return taskLatencyStats.getMax();
+    }
+}