Unable to get real time output from NSTask to NSTextView in release mode

I wasn't able to get real time output from NSTask to NSTextView in release mode. Already flushed the stdout as stated in https://developer.apple.com/forums/thread/112444.
Below is a snippet of my code:

 func displayOutput ( task:Process) {

        let outputPipe = Pipe()
        setvbuf(stdout, nil, IONBF, 0)
        dup2(outputPipe.fileHandleForReading.fileDescriptor, STDOUT_FILENO)
        task.standardOutput = outputPipe
        outputPipe.fileHandleForReading.waitForDataInBackgroundAndNotify()

        NotificationCenter.default.addObserver(forName: NSNotification.Name.NSFileHandleDataAvailable, object: outputPipe.fileHandleForReading , queue: nil) { notification in

            let output = outputPipe.fileHandleForReading.availableData
            let outputString = String(data: output, encoding: String.Encoding.utf8) ?? ""

            if outputString.count > 0 {

                DispatchQueue.main.async(execute: {
                    let previousOutput = self.outputTextView.string
                    let nextOutput = previousOutput + "\n" + outputString
                    self.outputTextView.string = nextOutput
                    let range = NSRange(location:nextOutput.count,length:0)
                    self.outputTextView.scrollRangeToVisible(range)
                })
            }         

outputPipe.fileHandleForReading.waitForDataInBackgroundAndNotify()
        }
    }