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2489 :: Where do I learn how to program Nim without a GC?

• Maxxi (orginal) [2016-08-24T09:21:40+02:00] view original

  I cant find any information. What happens if I use a nim library that uses a GC? I'll be "infected" with its problems. This entire situation seems terrible.

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• Araq (orginal) [2016-08-24T11:58:16+02:00] view original

  The no GC future is --gc:stack which replaces the GC with memory regions. So any library that uses the GC really uses a memory region. The entire situation is ok. Note that the GC is always thread local anyway, so you can also just run realtime threads with other threads that use the stdlib and thus the GC.

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• Krux02 (orginal) [2016-08-24T14:43:18+02:00] view original

  Is there any documentation on how this should work? How would it be possible to define a memory region and then later destroy it? And will there be a mechanism to test weather a memory region as still some active references in it?

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• Maxxi (orginal) [2016-08-25T13:16:08+02:00] view original

  Araq, I dont understand. I'm just now looking into Nimlang. How would I have to change the programming style to program with memory regions in Nim? It can't just be a flag to the compiler, I mean somehow I have to tell Nim when to free memory right?

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• flyx (orginal) [2016-08-25T13:47:51+02:00] view original

  I mean somehow I have to tell Nim when to free memory right?

  Yeah sure, you just use these: alloc, dealloc, allocShared, deallocShared. You can cast the pointer from and to ptr types and then you have your manually managed heap memory.

  (This is a general answer to how to use non-GC'd memory and has nothing to do with memory regions)

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• jyelon (orginal) [2016-08-25T16:25:26+02:00] view original

  Yeah, but he needs information on how to cause an normally garbage-collected library (for example, the JSON library) to allocate out of a memory region, without changing the code for the library. I think the real answer is: I don't think memory regions are implemented yet, I don't think anyone's really ironed out the details.

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• Araq (orginal) [2016-08-25T22:37:48+02:00] view original

  Compile with --gc:stack

  var rx: Region
  
  withRegion rx:
    ... json code here ...
  Run

  You're right though that it needs documentation. I don't even know if it's in 0.14.

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• andrea (orginal) [2016-08-26T10:15:59+02:00] view original

  @Araq Is there any discussion anywhere of the region memory model? You cannot expect people to just guess that it exists...

  I am not sure if this is supposed to work right now, but I tried

  import system/gc_stack
  
  var rx: Region
  
  withRegion rx:
    discard 0
  Run

  (compiling with --gc:stack) and I get the error

  
  lib/system/osalloc.nim(12, 3) Error: undeclared identifier: 'sysAssert'
  Run

  I am not sure I should import system/gc_stack but without it I cannot find the symbols Region and withRegion)

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• Araq (orginal) [2016-08-27T10:16:20+02:00] view original

  Well ok, it's called MemRegion, so this compiles with --gc:stack:

  var rx: MemRegion
  
  withRegion rx:
    discard 0
  Run

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