thread blocked indefinitely in an MVar operation

[diogob]

So this builds fine, runs the package tests fine, runs the NixOS integration test fine. But when I use it in my project, each websocket connection is immediately lost again and postgres-websockets shows this output:

thread blocked indefinitely in an MVar operation

In a loong debugging session I nailed this down to time-manager-0.1.2. 0.1.1 works fine, but 0.1.2 breaks it for us. Since you're not using that directly, I can only guess that it causes problems for code related to auto-update (?).

Maybe you have more insight, maybe you can reproduce, maybe you have any idea what's going on?

(the related change in that 0.1.1 -> 0.1.2 update was this PR: yesodweb/wai#1013)

Originally posted by @wolfgangwalther in #101 (comment)

[wolfgangwalther]

I made a simple test with the chat app, and this works fine - even with the latest dependencies.

---

So maybe there is something at play that is specific to the token we are sending.

The secret is development_secret_at_least_32_chars, the token is eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJyb2xlIiA6ICJwcmYzIiwgImV4cCIgOiAxNzQ3MjkwODcwLCAiY2hhbm5lbHMiIDogWyJwcmYzIl0sICJtb2RlIiA6ICJyIn0.SvZCiLjjIQgXC8n5Qu48FwcCTQ_twt3rwOEmds0CNZM.

The payload for that token is:

{
  "role": "prf3",
  "exp": 1747290870,
  "channels": [
    "prf3"
  ],
  "mode": "r"
}

I'm trying to put that into the chat app.

[wolfgangwalther]

This seems to only happen with mode: 'r'.

Edit: Yes, I can reproduce the error in the chat app, when setting mode: 'r' in the html file and then trying the connection. Note that this is also the case, when I remove the .send line from the function. So just opening the connection in read-only mode seems to be the problem.

[diogob]

Thanks again. I was able to reproduce it here as well. Will try to write a fix tonight.

[diogob]

Released the fix as 0.11.2.4

[wolfgangwalther]

Thank you very much for the quick fix :)