What is the intended method for catching exceptions raised from asyncCheck'd Futures? about nim-chronos HOT 4 CLOSED

you can:

proc process() {.async.} =
  raise (ref ValueError)()

proc ignoreExceptions(fut: Future[void]): Future[void] {.async.} =
  try:
    await fut
  except CatchableError as exc:
    debugEcho "fail"

asyncSpawn ignoreExceptions process()

asyncSpawn/asyncCheck exist to deliberately check for uncaught exceptions - just like raising in a thread without catching would terminate the program. discard process(...) will also make chronos ignore exceptions though it's poor style.

from nim-chronos.

if the user uses asyncSpawn, that's nothing you can control - there's no way to prevent that from raising a Defect - this is by design, the program would be in an inconsistent state at that point (because it would try to raise an exception through the processing loop which leads to resource leaks et al. This is a contributing reason why asyncdispatch has so many leaks and problems for example.

from nim-chronos.

Check, so this sentence of mine is incorrect:

I would like to be able to catch ValueError (or an exception containing it) outside of asyncProc, as "normal" errors such as this do not represent a sufficiently erroneous case to crash the thread to me.

Exceptions thrown by running the dispatcher instead of by some awaited future are a sufficiently erroneous case as you pointed out, due to potential resource leaks etc.

If I want to protect the user therefore my best choice is likely to mandate them not raise an exception, e.g via using raises: []

from nim-chronos.

mandate them not raise an exception,

indeed - it is likely asyncSpawn will start showing a compile-time warning whenever someone uses it without raises: []. asyncCheck is deprecated already for similar reasons.

from nim-chronos.