Reactive, Asynchronous, and Concurrent Programming

S

o far in this book you’ve seen functions and objects that process their inputs immediately using a single “thread” of execution where the code runs to completion and produces useful results or state changes. In this chapter, you’ll turn your attention to

concurrent, parallel, asynchronous

, and

reactive

programs. These each represent substantially different approaches to programming from those you’ve seen so far. Some of the reasons for turning to these techniques are as follows:

To achieve better responsiveness in a graphical user interface (GUI)

To report progress results during a long-running computation and to support cancellation of these computations

To achieve greater throughput in a reactive application or service

To achieve faster processing rates on a multiprocessor machine or cluster

To take advantage of the I/O parallelism available in modern disk drives or network connections

To sustain processing while network and disk I/O operations are in process In this chapter, we cover some of the techniques that can help achieve these outcomes:

Using .NET threads and the BackgroundWorker class for background computations

Using events and messages to report results back to a GUI

Using F# asynchronous workflows and the .NET thread pool to handle network requests and other asynchronous I/O operations

Using F# pattern matching to process message queues

Using low-level .NET shared-memory primitives to implement new concurrency techniques and control access to mutable data structures