Improve #3550 fix with a single Atomic

Signed-off-by: Greg Wilkins <gregw@webtide.com>

jetty-util/src/main/java/org/eclipse/jetty/util/AtomicWords.java

@@ -0,0 +1,182 @@
+//
+//  ========================================================================
+//  Copyright (c) 1995-2019 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;
+
+import java.util.concurrent.atomic.AtomicLong;
+
+/**
+ * An AtomicLong with additional methods to treat it as two hi/lo integers.
+ */
+public class AtomicWords extends AtomicLong
+{
+    /**
+     * Sets the hi and lo values.
+     *
+     * @param w0 the 0th word
+     * @param w1 the 1st word
+     * @param w2 the 2nd word
+     * @param w3 the 3rd word
+     */
+    public void set(int w0, int w1, int w2, int w3)
+    {
+        set(encode(w0, w1, w2, w3));
+    }
+
+    /**
+     * Atomically sets the word values to the given updated values only if
+     * the current encoded value is as expected.
+     *
+     * @param expectEncoded the expected encoded value
+     * @param w0 the 0th word
+     * @param w1 the 1st word
+     * @param w2 the 2nd word
+     * @param w3 the 3rd word
+     * @return {@code true} if successful.
+     */
+    public boolean compareAndSet(long expectEncoded, int w0, int w1, int w2, int w3)
+    {
+        return compareAndSet(expectEncoded,encode(w0, w1, w2, w3));
+    }
+
+    /**
+     * Atomically adds the given deltas to the current hi and lo values.
+     *
+     * @param delta0 the delta to apply to the 0th word value
+     * @param delta1 the delta to apply to the 1st word value
+     * @param delta2 the delta to apply to the 2nd word value
+     * @param delta3 the delta to apply to the 3rd word value
+     */
+    public void add(int delta0, int delta1, int delta2, int delta3)
+    {
+        while(true)
+        {
+            long encoded = get();
+            long update = encode(getWord0(encoded)+delta0,
+                getWord1(encoded)+delta1,
+                getWord2(encoded)+delta2,
+                getWord3(encoded)+delta3);
+            if (compareAndSet(encoded,update))
+                return;
+        }
+    }
+
+
+    /**
+     * Gets word 0 value
+     *
+     * @return the 16 bit value as an int
+     */
+    public int getWord0()
+    {
+        return getWord0(get());
+    }
+
+
+    /**
+     * Gets word 1 value
+     *
+     * @return the 16 bit value as an int
+     */
+    public int getWord1()
+    {
+        return getWord1(get());
+    }
+
+    /**
+     * Gets word 2 value
+     *
+     * @return the 16 bit value as an int
+     */
+    public int getWord2()
+    {
+        return getWord2(get());
+    }
+
+    /**
+     * Gets word 3 value
+     *
+     * @return the 16 bit value as an int
+     */
+    public int getWord3()
+    {
+        return getWord3(get());
+    }
+
+    /**
+     * Gets word 0 value from the given encoded value.
+     *
+     * @param encoded the encoded value
+     * @return the 16 bit value as an int
+     */
+    public static int getWord0(long encoded)
+    {
+        return (int) ((encoded>>48)&0xFFFFL);
+    }
+
+    /**
+     * Gets word 0 value from the given encoded value.
+     *
+     * @param encoded the encoded value
+     * @return the 16 bit value as an int
+     */
+    public static int getWord1(long encoded)
+    {
+        return (int) ((encoded>>32)&0xFFFFL);
+    }
+
+    /**
+     * Gets word 0 value from the given encoded value.
+     *
+     * @param encoded the encoded value
+     * @return the 16 bit value as an int
+     */
+    public static int getWord2(long encoded)
+    {
+        return (int) ((encoded>>16)&0xFFFFL);
+    }
+
+    /**
+     * Gets word 0 value from the given encoded value.
+     *
+     * @param encoded the encoded value
+     * @return the 16 bit value as an int
+     */
+    public static int getWord3(long encoded)
+    {
+        return (int) (encoded&0xFFFFL);
+    }
+
+    /**
+     * Encodes 4 16 bit words values into a long.
+     *
+     * @param w0 the 0th word
+     * @param w1 the 1st word
+     * @param w2 the 2nd word
+     * @param w3 the 3rd word
+     * @return the encoded value
+     */
+    public static long encode(int w0, int w1, int w2, int w3)
+    {
+        long wl0 = ((long)w0)&0xFFFFL;
+        long wl1 = ((long)w1)&0xFFFFL;
+        long wl2 = ((long)w2)&0xFFFFL;
+        long wl3 = ((long)w3)&0xFFFFL;
+        return (wl0<<48)+(wl1<<32)+(wl2<<16)+wl3;
+    }
+}