baz.nim

import os, threadpool

type
  ThreadSafeString* = distinct cstring

proc safe*(input: string): ThreadSafeString =
  var res = cast[cstring](allocShared(input.len + 1))
  copyMem(res, input.cstring, input.len)
  res[input.len] = '\0'
  res.ThreadSafeString

proc `$`*(input: ThreadSafeString): string =
  result = $(input.cstring)
  deallocShared input.cstring

proc sendSignal(data: ThreadSafeString, name: ThreadSafeString) =
  echo $name & ": " & $data

template spawnAndSend(name: ThreadSafeString, exprToSend: untyped) =
  proc payload() =
    let data: ThreadSafeString = exprToSend
    sendSignal(data, name)
  spawn payload()

proc foo(name: ThreadSafeString) =
  spawnAndSend(name) do:
    "foo".safe

foo("bar".safe)

sleep(2)

# Run with `./env.sh nim c -r --threads:on --tlsEmulation:off bar.nim`