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5318 :: Crashed when compiled as dynamic library for C

• Zachary (orginal) [2019-10-10T04:39:39+02:00] view original

  Hi all, I am a newbie to Nim and I have tried to write Nim as dynamic library for C, but I got some problems.

  person.nim:

  
  import strutils
  
  type
      Person = object of RootObj
          name*: string
          age*: Natural
  
  proc createPerson(n: int):ref Person {.cdecl, exportc: "createPerson", dynlib.} =
      var p = new(Person)
      p.age = 25
      p.name = newString(20)
      # p.name = format("jiazequn#$1", n)
      return p
  
  proc printPerson(p:ref Person) {.cdecl, exportc: "printPerson", dynlib.} =
      echo format("name is $1 and age is $2", p.name, p.age)
  
  proc nim_main() {.cdecl, exportc: "nim_main", dynlib.} =
      var num = 0
      while true:
          num += 1
          var p = createPerson(num)
          if num mod 10000 == 0:
              printPerson(p)
              echo num
  
  Run

  main.c

  
  #include <stdio.h>
  extern void nim_main();
  
  int main()
  {
      nim_main();
      return 0;
  }
  Run

  But I got the following errors when running after a while:

  
  name is  and age is 25
  2180000
  Traceback (most recent call last)
  /Users/zachary/Developer/nim-demo/person.nim(24) nim_main
  /Users/zachary/Developer/nim-demo/person.nim(16) printPerson
  /usr/local/Cellar/nim/1.0.0/nim/lib/pure/strutils.nim(2751) format
  /usr/local/Cellar/nim/1.0.0/nim/lib/system/gc.nim(439) newObj
  /usr/local/Cellar/nim/1.0.0/nim/lib/system/alloc.nim(777) rawAlloc
  SIGSEGV: Illegal storage access. (Attempt to read from nil?)
  Run

  It seems that it is the GC that cause this problem. If I disable the gc using GC_disable() at the beginning of nim_main(), no error occurred.

  Could you please give me some information about how to get it fixed?

  Also my final goal is to move nim_main function into main.c, now it have the similar problem.

  Thanks!

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• Araq (orginal) [2019-10-10T14:30:19+02:00] view original

  You need to also call NimMain at startup, generated by Nim.

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• Lachu (orginal) [2019-10-10T20:34:39+02:00] view original

  Also I thought new callable accept variable not a type. I remember it works like in Pascal - allocates memory and write pointer to this memory into given (as parameter) variable. In nim it also should initializes memory. Does your library compile?

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• Zachary (orginal) [2019-10-11T02:50:27+02:00] view original

  It works now! Thanks so much, it's of great help.

  I also got a question that since I have to call NimMain at startup, is it possible to use multiple nim dynamic libraries in one executable? Do I have to call every NimMain in these dynamic libraries or just one of them?

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• Zachary (orginal) [2019-10-11T02:52:34+02:00] view original

  In fact it works. The new function signature is

   new*(t: typedesc): auto =
  Run

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