🔗 To spawn, or not to spawn?

That is indeed the question! Whether it is better to keep everything in a single process, or to have a separate process for every piece of state we need to manage? In this post I’ll talk a bit about using and not using processes. I’ll also discuss how to separate complex stateful logic from concerns such as temporal behaviour and cross process communication.

But before starting, since this is going to be a long article, I want to immediately share my main points:

• Use functions and modules to separate thought concerns.
• Use processes to separate runtime concerns.
• Do not use processes (not even agents) to separate thought concerns.
• The construct “thought concern” here refers to ideas which exist in our mind, such as order, order item, and product for example. If those concepts are more complex, it’s worth implementing them in separate modules and functions to separate different concerns and keep each part of our code focused and concise.

Using processes (e.g. agents) for this is a mistake I see people make frequently. Such approach essentially sidesteps the functional part of Elixir, and instead attempts to simulate objects with processes. The implementation will very likely be inferior to the plain FP approach (or even an equivalent in an OO language). Keep in mind that there is a price associated with processes (memory and communication overhead). Therefore, reach for processes when there are some tangible benefits which justify that price. Code organization is not among those benefits, so that’s not a good reason for using processes.

Processes are used to address runtime concerns - properties which can be observed in a running system. For example, you’ll want to reach for multiple processes when you want to prevent a failure of one job to affect other activities in the system. Another motivation is when you want to introduce a potential for parallelism, allowing multiple jobs to run simultaneously. This can improve your performance, and open up potential for scaling in both directions. There are some other, less common cases for using processes, but again - separation of thought concerns is not one of them.