My company has a production system that uses core.async extensively. We've
been running it 24/7 for over a year with occasional restarts to update
things and add features, and so far core.async has been working great.
The other day, during a particularly high workload, the whole system got
locked up. All the channels seemed blocked at once. I was able to connect
with a REPL and poke around, and noticed strange behavior of core.async.
Specifically, the following code, when evaluated in the REPL, blocked on
the put (third expression):
(def c (async/chan))
(go-loop []
(when-some [x (<! c)]
(println x)
(recur)))
(>!! c true)
Whereas on any fresh system, the above expressions obviously succeed.
Puts succeeded if they went onto the channel's buffer, but not when they
should go through to a consumer. For example with the following
expressions, evaluated in the REPL, the first put succeeded (presumably
because it went on the buffer), but subsequent puts blocked:
(def c (async/chan 1))
(def m (async/mult c))
(def out (async/chan (async/sliding-buffer 3)))
(async/tap m out)
(>!! c true) ;; succeeds
(>!! c true) ;; blocks forever
This leads me to wonder if core.async itself somehow got into a bad state.
It's entirely possible I caused this by misusing the API somewhere in the
codebase, but we use core.async so extensively that I wouldn't know where
to begin looking.
I'm wondering if someone more familiar with core.async internals has an
idea about what could cause the above situation. Or if we notice it
happening again, what could I do to gather more helpful information.
I also have a redacted thread dump, in case it's useful:
https://gist.github.com/anonymous/65049ffdd37d43df8f23630928e8fed0
Any help would be much appreciated,
Aaron
P.S. core.async has been a godsend in terms of helping us structure and
modularize our large system. Thank you to all those who contributed to
this wonderful library!
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