Running tasks in parallel and asynchronously

One of the recurring problems that a developer has to face when working on integrating with external systems, is how to deal with sluggish response time.

Very often, a slow response time from a system, out of our control, ends up negatively affecting the user experience of a web application that feeds on the data coming from the slow system.

The first line of defense against such services is adding a caching layer. A cache helps to mitigate the effects of unreliable external systems, but it is not always the definitive cure. Depending on the business domain, a cache may have a large ratio of cache miss (occurs when a specific data is not found in the cache). Furthermore, on large systems caches can take time to warm up.

So, the second weapon in a developer arsenal against sleepy services, is using asynchronous calls. An asynchronous call is a non-blocking call to a method. A separate thread runs the method and returns the result whenever it is ready...