Scott Logic / Altogether Smarter
When WebAssembly was released a couple of years ago it was an MVP (Minimal Viable Product), having a small feature-set deemed just enough to make it useable and useful. One significant feature that was missing from the MVP was threads. The WebAssembly threads proposal is now quite mature and available in both the tooling and Chrome. This blog post explores the internals of this feature, the new instruction set, and how it supports multi-threaded applications.
Before delving into the details of the WebAssembly threads specification, I’m briefly going to talk about concurrency and threads, what they are, why we use them, and the challenges they present. If you’re old and wise, feel free to skip this section!
Modern computers have multiple CPUs (which themselves have multiple cores - but for simplicity I’ll refer to them simply as CPUs), each of which is able to execute programs independently. We can take advantage of this in various ways. For example, if you have a computationally intensive task such as image processing, you can split the work across multiple CPUs to get it done more quickly. Or, if you have a task that takes a modest amount of time (a second or two), you might want to handle this on a different CPU to the one that is updating your application UI, in order to preserve 60fps frame rate.
Threads are the underlying programming construct that allow you to divide work between these CPUs. There isn’t a direct mapping between threads and CPU, but in practice, in order to achieve concurrency you need to create multiple threads.
