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12510 :: Spawning procs returning strings

• Nimnoob7 (orginal) [2024-09-10T20:40:05+02:00] view original

  Hi,

  I need to spawn threads that return a string. When I use the deprecated threadpool library, I end up having some sort of arbitrary memory leak when reusing flowvar objects for sequential spawn->sync operations and changing to taskpools does not seem to work at all:

  import taskpools

  var pool = Taskpool.new(num_threads = 4)

  proc dostuff(): string =

  return "testtest"

  var flow = pool.spawn dostuff()

  stack trace: (most recent call last)

  /playground/nimble/taskpools-0.0.5-a01ff26051e7fa5a94591925144ff63aa70f225a/taskpools/channels_spsc_single.nim(60, 11) trySend

  /playground/nim/lib/std/assertions.nim(41, 14) failedAssertImpl

  /playground/nim/lib/std/assertions.nim(36, 13) raiseAssert

  /playground/nim/lib/system/fatal.nim(53, 5) sysFatal

  /usercode/in.nim(8, 16) template/generic instantiation of `spawn` from here

  /playground/nimble/taskpools-0.0.5-a01ff26051e7fa5a94591925144ff63aa70f225a/taskpools/taskpools.nim(479, 21) template/generic instantiation of `readyWith` from here

  /playground/nimble/taskpools-0.0.5-a01ff26051e7fa5a94591925144ff63aa70f225a/taskpools/flowvars.nim(53, 38) template/generic instantiation of `trySend` from here

  /playground/nim/lib/system/fatal.nim(53, 5) Error: unhandled exception: /playground/nimble/taskpools-0.0.5-a01ff26051e7fa5a94591925144ff63aa70f225a/taskpools/channels_spsc_single.nim(60, 11) `supportsCopyMem(T)` Channel is not garbage-collection-safe [AssertionDefect]

  Is there a simple way to spawn procs that strings?

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• Hobbyman (orginal) [2024-09-10T21:45:05+02:00] view original

  Have you tried malebolgia?

  https://www.youtube.com/watch?v=MIITSTQok-4

  using the => operator?

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• Nimnoob7 (orginal) [2024-09-10T21:57:29+02:00] view original

  So threads will be spawned at various locations, and I need a way to check if they are "done", like isReady, and Malebolgia does not appear to support that.

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• Hobbyman (orginal) [2024-09-10T22:13:51+02:00] view original

  Oh sorry, i didnt realize that. It seems Malebolgia doesnt seem to support random spawning and intermittent testing / aborting. I assume that is unstructured concurrency..

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• rusty (orginal) [2025-08-05T20:56:39+02:00] view original

  I get the same problem with taskpools on nim-2.2.4. If my spawned proc returns a number it works, but trying to return a string draws the same error: "Channel is not garbage-collection-safe".

  Any ideas on how to fix this?

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