Add ContentSize() to cheaply calculate the size of the ring buffer

ring.go

@@ -35,6 +35,21 @@ func (r Ring) Capacity() int {
 	return len(r.buff)
 }
 
+/*
+ContentSize returns the current number of elements inside the ring buffer.
+*/
+func (r *Ring) ContentSize() int {
+	if r.head == -1 {
+		return 0
+	} else {
+		difference := (r.head - r.tail)
+		if difference < 0 {
+			difference = -difference
+		}
+		return difference + 1
+	}
+}
+
 /*
 Enqueue a value into the Ring buffer.
 */