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()         }     }

I wanted to display output from Process() to NSTextView in real time. Below are my code snippets: func displayOutput (_ task:Process) { let outputPipe = Pipe() setvbuf(stdout, nil, _IONBF, 0) dup2(outputPipe.fileHandleForWriting.fileDescriptor, STDOUT_FILENO) task.standardOutput = outputPipe outputPipe.fileHandleForReading.readabilityHandler = { pipe in if let outputString = String(data: pipe.availableData, encoding: String.Encoding.utf8) { if outputString.count > 0 { DispatchQueue.main.async(execute: { print(outputString, separator: "\n", to: &self.outputTextView.string) let range = NSRange(location:self.outputTextView.string.count,length:0) 	self.outputTextView.scrollRangeToVisible(range) } } } } } The above code snippets only works in debug mode. Nothing displays on the NSTextView besides the initial text when it's in release mode.