Futures and blocking

Examples in this book should have shed the light into why blocking is sometimes considered an anti-pattern. Futures and asynchronous computations mainly exist to avoid blocking, but in some cases, we cannot live without it. It is therefore valid to ask how blocking interacts with futures.

There are two ways to block with futures. The first is waiting until a future is completed. The second is blocking from within an asynchronous computation. We will study both the topics in this section.

Awaiting futures

In rare situations, we cannot use callbacks or future combinators to avoid blocking. For example, the main thread that starts multiple asynchronous computations has to wait for these computations to finish. If an execution context uses daemon threads, as is the case with the global execution context, the main thread needs to block to prevent the JVM process from terminating.

In these exceptional circumstances, we use the ready and result methods on the Await object from...