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This article will be the final third of my investigation, looking at sequencing and threading in Combine; what guarantees does Combine offer for thread safety and delivery order. I'll finish up with a quick look at Combine's performance.
I'll explain why I consider reactive programming to be one of the most important design patterns for application programming by looking at three scenarios that are common in application development, yet are a drain on development time, lead to frequent bugs and make design and refactoring hard. I'll show how reactive programming addresses the verbosity, eliminates the unsafety and restructures the code to aid maintainability.
In this article, I'm presenting CwlSignal. It is the latest Swift iteration of a library that I've been using for reactive programming for the last few years. CwlSignal is simple, fast, threadsafe and full-featured while offering a number of unique abilities.
Testing that actions are scheduled correctly over time is a pain. I'll show a way to test events scheduled over time, threads and other execution contexts with a "Debug Context Coordinator" that functions as a basic task scheduler but operates over a simulated version of time so that testing of invocation times and task interaction can be precise and free from changes due to host activity.
I take a look at what's involved in specifying the 'execution context' in which a function should be invoked. It's a complicated task due to how broad the term 'execution context' can be, as well as the fact that both function caller and function callee may have conflicting desires for how a function should be invoked.
I look at usage patterns around timers including some problematic approaches that can make refactoring more difficult, cause strange bugs and otherwise create problems for maintainability.
I'm going to talk about the absence of any threading or thread synchronization language features in Swift and the concurrency proposal for Swift's future. I'll also try to get a wrapper around different mutex machinery to perform optimally.
