Can timbre use pprint from multiple threads? about timbre

[ptaoussanis]

Hi Ikrubner,

This does look like a concurrency issue. You've got multiple threads all trying to print as quickly as they can, and their output is getting mangled together. Think of a room filled with people all shouting at once: you won't be able to hear what anyone's saying because they're all talking over each other.

In particular, this can happen because prn, println, pprint, etc. call (flush) whenever they have something to print. In a single-threaded app, that's usually what you want. But for multi-threaded cases like yours, you'd rather have the output buffered and only (flush)ed as a single atomic output. With the room-of-people analogy, everyone's still shouting together but now at least they're each shouting a complete sentence one at a time without interruption.

I'd start by trying this:
Don't call pprint 3 separate times for each thing you want to output. Each of those 3 calls will (flush), meaning other gook can get interleaved in between. Instead, I'd do something like this:

(let [output (with-out-str (pp/pprint prefix) (pp/pprint message) (pp/pprint more))]
  (print output)
  (flush))

By buffering up the pprint outputs, that also protects against any flushing that may be happening within the pprint calls itself (I just skimmed the source now, not sure if that's necessary or not).

In some cases it can also help to enable :async? for the appender.

Try those out and let me know if you have any luck.

Cheers!

[lkrubner]

That worked great. Thanks.

[ptaoussanis]

Sure, no problem!