How does Volley singleton execute concurrent requests when a thread pool uses a single instance of an HTTP client?

Question

When one RequestQueue volleyball is created, it initializes the BasicNetwork object using an http client. It also creates a default thread pool of 4 to receive requests from the queue and execute them.

Now there is only 1 BasicNetwork object in the queue, and the BasicNetwork.this.performRequest (...) method is a blocking call. So how does Volley parallelize queries?