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10390 :: Some ideas about nimrtl

• sls1005 (orginal) [2023-08-09T10:52:36+02:00] view original

  I've recently found that it's possible to register a callback to a dynamically loaded library and invoke it.

  For example:

  # test0.nim
  # nim c --app:lib --noMain test0.nim
  var registered: proc(p: ptr int) {.nimcall.}
  
  proc registerFn(fn: proc(p: ptr int) {.nimcall.}) {.exportc, dynlib, nimcall.} =
    registered = fn
  
  proc invokeWith(p: ptr int) {.exportc, dynlib, nimcall.} =
    registered(p)
  Run

  # test1.nim
  proc initModuleTest0() {.importc: "NimMain", cdecl, dynlib: "./libtest0.so".}
  
  proc registerFn(fn: proc(p: ptr int) {.nimcall.}) {.importc, nimcall, dynlib: "./libtest0.so".}
  
  proc invokeWith(p: ptr int) {.importc, nimcall, dynlib: "./libtest0.so".}
  
  proc f(p: ptr int) =
    inc(p[])
  
  var x = 0
  initModuleTest0()
  registerFn(f)
  invokeWith(x.addr)
  echo x
  Run

  (I know such code currently have multi-GC problem with refc, because I'm not using -d:useNimrtl and both the main program and the library have GCs.)

  Anyway, I think the main program can serve as the role nimrtl usually has, by registering GC-related callbacks to libraries being loaded, using this technique, and thus avoid to have multi-GC.

  As ORC has become the default strategy and doesn't have the multi-GC problem, such problem has become less important, I think.

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