I have something similar to the following code: genserver_name = "cool_name" task = Task.async(fn -> MyModule.start() end) :timer.sleep(500) GenServer.cast(genserver_name, {:save, first_payload}) GenServer.cast(genserver_name, {:save, second_payload}) GenServer.cast(gense…

Because you’re spawning a task that then spawns the server you’re hitting a race condition. The named server doesn’t exist yet. Rather than using a timer (which either wastes time or cuts it too close and has a chance of failure), you can try GenServer.whereis . If it returns nil then the named serve…

No problem. I recommend drawing out problems like this. Here is my approximation of what’s happening as an image: [SoWkIImgAStDuIe0qfd9cGM9UIKAkOcPUQW2-NcP9Vb5A6B5gKLbgKLSN2352hfsS3M9oIMPPOabgJ01c88AY0x2VAW-e114164aZ9-I2XD1CSC6xWfa9N0XXzIy5A1F0G00] The blocks in each column represent the processe…

Which tool do you use for these diagrams?

PlantUML. There’s a nice live preview in VS Code with it via the PlantUML extension by jebbs. I also make these sorts of diagrams (when I want more freeform charts) with Graphviz and use the Graphviz extension by João Pinto for live previews of those.

One question that left me scratching my head: How were you able to get a GenServer named with a binary? Typically names are only allowed to be atoms, {:global, term}, or {:via, module, term}. I feel like there’s something unidiomatic going on under the hood which is causing these issues. If you …

Also genserver_name is not given to MyModule.start() in the example.

@lud @ityonemo Thank you for your responses! @lud yes, you are right, but it knows the correct name. In the actual use case, this module receives various parameters and generates the GenServer name based on them. I just wanted to simplify the example and didn’t specify this, I’m sorry about that. T…

Cool! Just a few more things. Beware that {:global, id} is a bit dangerous in that if you ever go to distributed beam, startup of the process will require a full distributed transaction lock (with a not very fast consensus protocol, aka, not even Paxos/Raft IIRC) to make sure it’s “truly global”. …

Thank you for the suggestions again! I haven’t used Task.Supervised yet, I’ll look into it. One possible complication might come from the fact that payloads in my case are saved in the state of the aforementioned GenServer from different processes. For instance, if I have 3 payloads, they are receiv…

If you need a canonical name, use registry :slight_smile: it’s exactly what you propose (ets table). And you can certainly register a task with registry.

Elixir Programming Language Forum

GenServer blocking in async task

Questions & Help Questions

nikody June 25, 2020, 4:34pm 3

Ah, how didn’t I think of that! Thank you!