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9432 :: Thread-Safe Container Type doubts

• JeysonFlores (orginal) [2022-09-03T07:55:30+02:00] view original

  Hello guys I'm trying to make a type definition that can be used to store generic data that could be used from different threads and async procedures. I looked up that in order to perform thread-safe reads/writes I have to use a Lock. I made it to this:

  import locks
  
  type
    Foo[T] = ref object
      value: T
      lock: Lock
  
  proc newFoo[T](value: T): Foo[T] =
    var newLock: Lock
    var newValue {.guard: newLock.} = value
    Foo[T](value: newValue, lock: newLock)
  
  Run

  And the procedures to make writes/reads are these:

  proc getValue[T](self: Foo[T]): T =
    var result: T
    withLock self.lock:
      result = self.value
    result
  
  proc setValue[T](self: Foo[T], value: T) =
    withLock self.lock:
      self.value = value
  Run

  However when I run this code with actual data it gives the following warnings:

  let foo = newFoo[string]("default")
  
  echo foo.getValue
  
  foo.setValue("If you're able to read this, it works!")
  
  echo foo.getValue
  Run

  
  /path/to/file.nim(25, 9) template/generic instantiation of `getValue` from here
  /path/to/file.nim(14, 7) Warning: Special variable 'result' is shadowed. [ResultShadowed]
  default
  If you're able to read this it works!
  Run

  Even though it shows the expected results these warnings are bothering me. Specially since the result variable int the getValue has to be used to return safely the value, otherwise it throws error since the procedure ends without closing the lock. Is there any suggestion or opinion? Thanks

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• Araq (orginal) [2022-09-03T10:54:39+02:00] view original

  Instead of

  proc getValue[T](self: Foo[T]): T =
    var result: T
    withLock self.lock:
      result = self.value
    result
  Run

  use:

  proc getValue[T](self: Foo[T]): T =
    withLock self.lock:
      result = self.value
  Run

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• JeysonFlores (orginal) [2022-09-03T18:37:03+02:00] view original

  Thanks! It works without problem

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