Dave discusses an alternate component-based approach to writing GenServers. This consists of modules in three files:

• A public API to hide the GenServer complexity.
• The GenServer interface.
• Implementatation.

The public API is just a wrapper to the GenServer functions and the GenServer functions are just a wrapper to the implementation. This hides the GenServer call/cast complexity and isolates the implementation.

I like this approach, but think that breaking it into three files is too complex. If the public API is only a wrapper to the GenServer API and the GenServer API is only a wrapper to the implementation, we can easily put them into a single file.

My approach implements the GenServer in two files:

• Public API which calls the GenServer functions.
• Implementation

Update 2023-02-16: I’m generally working a bit beyond my postings. In retrospect, I should have broken the public API and the GenServer interface into two modules, and kept them in the same file. I may have focused too much on the author breaking the modules into separate files. Keeping these initial thoughts to reflect my thinking at the time.

1. An OTP server (GenServer) is a module containing one or more callbacks functions with standard names.

2. Handler functions get passed the current state and return a potentially updated state.

3. The handle_call function pattern matches on the message.

4. Use a tuple to one of several identifiers to a server function.

5. Use debug_trace to log message activity.

   GenServer.start_link(..., [debug: [:trace]])

6. :statistics is another useful debug option. Display them as follows:

   :sys.statistics pid, :get

OTP-Servers-1

Source code to create a server that implements a stack and pop.

OTP-Servers-2

Source code to implement pop. Return nil when the stack is empty.

OTP-Servers-3 and OTP-Servers-4

Source code to name the server and implement the API in the same file.

Source code for alternate solution with implementation separated out. I like this approach when the module is complex.

OTP-Servers-5

Source code to implement terminate callback.

All notes and comments are my own opinion. Follow me at @rgacote@genserver.social