Fix potential issues of LinkedListQueue.

Author: johnteee

queue.go

@@ -340,12 +340,23 @@ func (q *LinkedListQueue[T]) Poll() (T, error) {
 	return q.Shift()
 }
 
+// Peek Peek the T val from the first position without removing it (non-blocking)
+func (q *LinkedListQueue[T]) Peek() (T, error) {
+	node := q.first
+	if node == nil {
+		return *new(T), ErrQueueIsEmpty
+	}
+	return *node.Val, nil
+}
+
 // Shift Shift the T val from the first position (non-blocking)
 func (q *LinkedListQueue[T]) Shift() (T, error) {
 	node := q.first
 	if node == nil {
 		return *new(T), ErrQueueIsEmpty
 	}
+
+	// Remove the first item
 	q.count--
 	q.first = node.Next
 	if q.first == nil {
@@ -369,6 +380,9 @@ func (q *LinkedListQueue[T]) Unshift(val T) error {
 	node.Val = &val
 
 	q.count++
+	if q.last == nil {
+		q.last = node
+	}
 	first := q.first
 	q.first = node
 	node.Next = first

queue_test.go

@@ -237,4 +237,22 @@ func TestLinkedListQueue(t *testing.T) {
 	assert.Equal(t, 0, linkedListQueue.Count())
 	assert.Equal(t, 0, linkedListQueue.nodeCount)
 	assert.Nil(t, linkedListQueue.nodePoolFirst)
+
+	go func() {
+		time.Sleep(1 * time.Millisecond)
+
+		for i := 1; i <= 10000; i++ {
+			result, err := concurrentQueue.Take()
+			assert.Equal(t, nil, err)
+			assert.Equal(t, i, result)
+		}
+	}()
+	go func() {
+		for i := 1; i <= 10000; i++ {
+			err := concurrentQueue.Offer(i)
+			assert.Equal(t, nil, err)
+		}
+	}()
+
+	time.Sleep(2 * timeout)
 }