NotificationCenter notification doesn't occur until user drop SliderUI

Question

I have:

• run Procces in MacOS SwiftUI application

• UI Slider widget that updated value and force Process to perform some job.

• Handler process responses (NotificationCenter.default.addObserver)

    outHandle  = FileHandle()
    outputPipe = Pipe()
    inputPipe  = Pipe()
    process    = Process()
  
    process.standardInput       = inputPipe
    process.standardOutput      = outputPipe
  
    outHandle = outputPipe.fileHandleForReading
    outHandle.waitForDataInBackgroundAndNotify()
  
    var observer : NSObjectProtocol!
  
    observer = NotificationCenter.default.addObserver(forName: NSNotification.Name.NSFileHandleDataAvailable, object: outHandle, queue: nil) {  notification -> Void in
    let data = self.outHandle.availableData // #1
    ...
    }
  

  try process.run()

---

View:

Slider(value: Binding(
     get: { myValue }, 
     set: { (newVal) in  
              myValue = newValue  
              inputPipe.fileHandleForWriting.write("{ value: \(myValue) }") // #2 
          }), in: 0...1)

Requests to process (comment #2) sends simultaniously to slider moving and I see process writes result into console. I expect handler of observer (comment #1) will run simultaniosly to process responses. But line (comment #1) executes only after I drop (mouseUP) slider.

If I move slider very fast and drop it (mouseUP) and process doesn't responded for all request yet - I will enter into #1 several times (for each process response that was occur after interaction with slider finished). If I move slider very slow so process responded to all request during movement - after dropping (mouseUP) slider #1 executes only one time (for last process response).

Tried to use different values of queue: OperationQueue.main, OperationQueue.current, nil.