#8414: fix drainTo when head == tail but the queue isn't empty

Signed-off-by: Ludovic Orban <lorban@bitronix.be>

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

@@ -608,13 +608,19 @@ public class BlockingArrayQueue<E> extends AbstractList<E> implements BlockingQu
             _headLock.lock();
             try
             {
+                if (_size.get() == 0)
+                    return 0;
+
                 final int head = _indexes[HEAD_OFFSET];
                 final int tail = _indexes[TAIL_OFFSET];
                 final int capacity = _elements.length;
 
                 int i = head;
-                while (i != tail && elements < maxElements)
+                while (elements < maxElements)
                 {
+                    if (i == tail && elements > 0)
+                        break;
+
                     elements++;
                     c.add((E)_elements[i]);
                     ++i;

jetty-util/src/test/java/org/eclipse/jetty/util/BlockingArrayQueueTest.java

@@ -28,6 +28,7 @@ import org.hamcrest.Matchers;
 import org.junit.jupiter.api.Test;
 
 import static org.awaitility.Awaitility.await;
+import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
@@ -38,7 +39,7 @@ import static org.junit.jupiter.api.Assertions.fail;
 public class BlockingArrayQueueTest
 {
     @Test
-    public void testWrap() throws Exception
+    public void testWrap()
     {
         BlockingArrayQueue<String> queue = new BlockingArrayQueue<>(3);
 
@@ -78,7 +79,7 @@ public class BlockingArrayQueueTest
     }
 
     @Test
-    public void testRemove() throws Exception
+    public void testRemove()
     {
         BlockingArrayQueue<String> queue = new BlockingArrayQueue<>(3, 3);
 
@@ -100,7 +101,7 @@ public class BlockingArrayQueueTest
     }
 
     @Test
-    public void testLimit() throws Exception
+    public void testLimit()
     {
         BlockingArrayQueue<String> queue = new BlockingArrayQueue<>(1, 0, 1);
 
@@ -113,7 +114,7 @@ public class BlockingArrayQueueTest
     }
 
     @Test
-    public void testGrow() throws Exception
+    public void testGrow()
     {
         BlockingArrayQueue<String> queue = new BlockingArrayQueue<>(3, 2);
         assertEquals(3, queue.getCapacity());
@@ -339,7 +340,7 @@ public class BlockingArrayQueueTest
     }
 
     @Test
-    public void testRemoveObjectWithWrappedTail() throws Exception
+    public void testRemoveObjectWithWrappedTail()
     {
         BlockingArrayQueue<String> queue = new BlockingArrayQueue<>(6);
         // Wrap the tail
@@ -361,7 +362,7 @@ public class BlockingArrayQueueTest
     }
 
     @Test
-    public void testRemoveObject() throws Exception
+    public void testRemoveObject()
     {
         BlockingArrayQueue<String> queue = new BlockingArrayQueue<>(4, 0, 4);
 
@@ -395,7 +396,7 @@ public class BlockingArrayQueueTest
     }
 
     @Test
-    public void testRemoveWithMaxCapacityOne() throws Exception
+    public void testRemoveWithMaxCapacityOne()
     {
         BlockingArrayQueue<String> queue = new BlockingArrayQueue<>(1);
 
@@ -408,7 +409,7 @@ public class BlockingArrayQueueTest
     }
 
     @Test
-    public void testIteratorWithModification() throws Exception
+    public void testIteratorWithModification()
     {
         BlockingArrayQueue<String> queue = new BlockingArrayQueue<>(4, 0, 4);
         int count = queue.getMaxCapacity() - 1;
@@ -430,7 +431,7 @@ public class BlockingArrayQueueTest
     }
 
     @Test
-    public void testListIterator() throws Exception
+    public void testListIterator()
     {
         BlockingArrayQueue<String> queue = new BlockingArrayQueue<>(4, 0, 4);
         String element1 = "A";
@@ -464,7 +465,7 @@ public class BlockingArrayQueueTest
     }
 
     @Test
-    public void testListIteratorWithWrappedHead() throws Exception
+    public void testListIteratorWithWrappedHead()
     {
         BlockingArrayQueue<String> queue = new BlockingArrayQueue<>(4, 0, 4);
         // This sequence of offers and polls wraps the head around the array
@@ -504,7 +505,7 @@ public class BlockingArrayQueueTest
     }
 
     @Test
-    public void testDrainTo() throws Exception
+    public void testDrainTo()
     {
         BlockingArrayQueue<String> queue = new BlockingArrayQueue<>();
         queue.add("one");
@@ -525,4 +526,30 @@ public class BlockingArrayQueueTest
         assertThat(queue.size(), Matchers.is(0));
         assertThat(queue, Matchers.empty());
     }
+
+    @Test
+    public void testDrainToAtDefaultGrowthSize()
+    {
+        BlockingArrayQueue<Integer> queue = new BlockingArrayQueue<>();
+        for (int i = 0; i < BlockingArrayQueue.DEFAULT_GROWTH * 2; i++)
+        {
+            queue.add(i);
+        }
+
+        List<Integer> list = new ArrayList<>();
+        assertThat(queue.drainTo(list), is(BlockingArrayQueue.DEFAULT_GROWTH * 2));
+        assertThat(list.size(), is(BlockingArrayQueue.DEFAULT_GROWTH * 2));
+        assertThat(queue.size(), is(0));
+    }
+
+    @Test
+    public void testDrainToAtZeroSize()
+    {
+        BlockingArrayQueue<Integer> queue = new BlockingArrayQueue<>();
+
+        List<Integer> list = new ArrayList<>();
+        assertThat(queue.drainTo(list), is(0));
+        assertThat(list.size(), is(0));
+        assertThat(queue.size(), is(0));
+    }
 }