Parallel asynchronous operation patterns

A common source of bad performance is running operations sequentially that could be completed in parallel.

For example, a naive implementation of loading a cart and then the contained products would be as follows:

Figure 7.2: Load cart then each of the three products contained from fakestoreapi

In this case, the operation completion time is composed of the sum of the following:

• Request-response time for GET /carts/{cartId}
• Request-response time for GET /products/1
• Request-response time for GET /products/2
• Request-response time for GET /products/3

There is a requirement for the /products/{productId} calls to be done after the GET /carts/{cartId} call completes since that’s where the product IDs are coming from. What isn’t required is for each product call to wait for the previous one to complete; the calls only depend on data from the GET /carts/{cartId} call. This is an...