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6645 :: How to implement a single table that all threads can access?

• jasonfi (orginal) [2020-08-06T14:54:20+02:00] view original

  I want to store a table[string, string] that any thread can access. I know this would mean using a lock for thread-safety.

  The closest example I could find to implementing this approach is: https://simpletutorials.com/c/nim/vz4pqar9/how-to-read-global-data-from-a-thread-in-nim

  PMunch on IRC had concerns that the default GC couldn't handle this, because Nim's heap is thread-local, and one thread could alloc a string, with another thread trying to free it incorrectly, and that this could introduce a bug.

  Another potential way is to have one thread that owns the table, but I don't know how the other threads would be able to find it.

  Has anyone done something like this successfully?

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• Yardanico (orginal) [2020-08-06T14:56:40+02:00] view original

  Guess what? We have https://nim-lang.org/docs/sharedtables.html in stdlib, not sure if it works well though

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• jasonfi (orginal) [2020-08-06T15:55:00+02:00] view original

  They say not to use GC'd keys and values with sharedtables on the docs page, strings are GC'd right?

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• quetzalb (orginal) [2020-08-06T17:10:15+02:00] view original

  One option is to spawn a thread that owns the table, and update it or query it from other threads by sending requests over a channel.

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• jasonfi (orginal) [2020-08-06T18:11:06+02:00] view original

  That is one approach I was thinking about going with, I was just hoping to avoid any overhead that would go with sending messages over channels (hopefully not too much). If nobody mentions a more direct way then I'll go with this approach, thanks!

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• filcuc (orginal) [2020-08-06T20:46:20+02:00] view original

  Use a mutex

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• jibal (orginal) [2020-08-06T20:55:42+02:00] view original

  That's not the issue ... read the OP's question again.

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• filcuc (orginal) [2020-08-07T00:39:35+02:00] view original

  Possible solutions:

  • manual GC ref / unref
  • use deepcopy with mutex
  • use ARC and latest nim

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• jasonfi (orginal) [2020-08-07T06:51:05+02:00] view original

  Thanks. I'll go with ARC and the latest Nim, but it's good to know what the options are. This should be in the Nim docs somewhere.

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