NODE JS - Event demultiplexing

 Busy-waiting is definitely not an ideal technique for processing non-blocking resources, but luckily, most modern operating systems provide a native mechanism to handle concurrent, non-blocking resources in an efficient way; this mechanism is called synchronous event demultiplexer or event notification interface. This component collects and queues I/O events that come from a set of watched resources, and block until new events are available to process. The following is the pseudocode of an algorithm that uses a generic synchronous event demultiplexer to read from two different resources:

The previous image helps us understand how concurrency works in a single-threaded application using a synchronous event demultiplexer and non-blocking I/O. We can see that using only one thread does not impair our ability to run multiple I/O bound tasks concurrently. The tasks are spread over time, instead of being spread across multiple threads. This has the clear advantage of minimizing the total idle time of the thread, as clearly shown in the image. This is not the only reason for choosing this model. To have only a single thread, in fact, also has a beneficial impact on the way programmers approach concurrency in general. Throughout the book, we will see how the absence of in-process race conditions and multiple threads to synchronize, allows us to use much simpler concurrency strategies. In the next chapter, we will have the opportunity to talk more about the concurrency model of Node.js.

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