Hey Jeremy,
We currently use Sequel with Sharded Connection Pooling (5-10 threads
usually) in our codebase, connecting to postgres instances, along with some
select usages of Async blocks using the Async gem. All is working great,
but recently I wanted to try enabling the fiber_concurrency extension to
see if that would squeeze out any additional performance gains. As soon as
I enabled it, some of our tests broke, specifically in scenarios where an
Async block was used in the context of a model. I started seeing errors
like this:
0.0s warn: Async::Task [oid=0x27ee8] [ec=0x27efc] [pid=4388]
[2023-07-21 08:48:12 -0700]
| Task may have ended with unhandled exception.
| NoMethodError: undefined method `foo' for nil:NilClass
where foo was a method on some model called within an Async block. The
really strange thing, in one case, is that it only threw the error if
calling refresh on the model right before hand. ie given this test
scernario:
models = create models
do some updates on the models
models.each(&refresh)
Model.some_function_with_async_block(models)
dies with above exception where foo was called within the async block in
some_function_with_async_block.
However, if I remove the call to refresh, it all works fine!
In another case, there was a a model that had a function with an async
block, and in that block it called another model to get some records. With
fiber_concurrency on, that dataset was returning nothing when called inside
the block. In this case, it didn't need to be in the async block, so moving
it outside is a fine solution, but these issues are a bit scary to say the
least.
Do you have any idea what might be going on here? I've been trying in vain
to setup a small reproduction
here: https://github.com/mscrivo/sequel-async-bug but have so far been
unable to reproduce the exact conditions that trigger the issue in our
codebase. I'm not sure if it's pg specific, or some other piece of code in
our codebase interacting badly with the fiber_concurrency and async.
Thanks!
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