Fixes #216: Size of SpscGrowableArrayQueue can exceeds max capacity

Adjust producer limit in order to allow one more element to be added
in place of the unneeded JUMP when the max capacity producer buffer
has been allocated

jctools-core/src/main/java/org/jctools/queues/SpscGrowableArrayQueue.java

@@ -114,7 +114,7 @@ final boolean offerColdPath(
                     long currConsumerIndex = lvConsumerIndex();
                     // use lookAheadStep to store the consumer distance from final buffer
                     this.lookAheadStep = -(index - currConsumerIndex);
-                    producerBufferLimit = currConsumerIndex + maxCapacity - 1;
+                    producerBufferLimit = currConsumerIndex + maxCapacity;
                 }
                 else
                 {

jctools-core/src/main/java/org/jctools/queues/atomic/SpscGrowableAtomicArrayQueue.java

@@ -106,7 +106,7 @@ final boolean offerColdPath(final AtomicReferenceArray<E> buffer, final long mas
                     long currConsumerIndex = lvConsumerIndex();
                     // use lookAheadStep to store the consumer distance from final buffer
                     this.lookAheadStep = -(index - currConsumerIndex);
-                    producerBufferLimit = currConsumerIndex + maxCapacity - 1;
+                    producerBufferLimit = currConsumerIndex + maxCapacity;
                 } else {
                     producerBufferLimit = index + producerMask - 1;
                     adjustLookAheadStep(newCapacity);

jctools-core/src/test/java/org/jctools/queues/QueueSanityTestSpscGrowable.java

@@ -2,13 +2,17 @@
 
 import org.jctools.queues.spec.ConcurrentQueueSpec;
 import org.jctools.queues.spec.Ordering;
+import org.junit.Assert;
+import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.Parameterized;
 
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Queue;
 
+import static org.hamcrest.Matchers.is;
+
 @RunWith(Parameterized.class)
 public class QueueSanityTestSpscGrowable extends QueueSanityTest
 {
@@ -27,4 +31,30 @@ public static Collection<Object[]> parameters()
         return list;
     }
 
+    @Test
+    public void testSizeNeverExceedCapacity()
+    {
+        final SpscGrowableArrayQueue<Integer> q = new SpscGrowableArrayQueue<>(8, 16);
+        final Integer v = 0;
+        final int capacity = q.capacity();
+        for (int i = 0; i < capacity; i++)
+        {
+            Assert.assertTrue(q.offer(v));
+        }
+        Assert.assertFalse(q.offer(v));
+        Assert.assertThat(q.size(), is(capacity));
+        for (int i = 0; i < 6; i++)
+        {
+            Assert.assertEquals(v, q.poll());
+        }
+        //the consumer is left in the chunk previous the last and biggest one
+        Assert.assertThat(q.size(), is(capacity - 6));
+        for (int i = 0; i < 6; i++)
+        {
+            q.offer(v);
+        }
+        Assert.assertThat(q.size(), is(capacity));
+        Assert.assertFalse(q.offer(v));
+    }
+
 }