[swift-users] GCD and Process

[Shawn Erickson]

It looks like you aren't keeping your app alive to allow the secondary
queue to reliably execute the closures you queue with it. It isn't really
clear what you want to attempt so it hard to suggest the correct way to do
things.

-Shawn
On Thu, Jan 5, 2017 at 11:39 PM Mr Bee via swift-users <
swift-users at swift.org> wrote:

> Hi all,
>
> I'm currently still learning Swift 3. Now I'm playing around with GCD
> (grand central dispatch). I'd like to start an external process using
> Process from an asynced thread, and create another thread to stop that
> external process after some times. Here's what I do…
>
> import Foundation
> import Dispatch
>
> extension Process {
>   func execute(command: String, currentDir: String = "~", arguments: [
> String] = [], input: String = "") -> String {
>     if !input.isEmpty {
>       let pipeIn = Pipe()
>       self.standardInput = pipeIn
>       *// multiple inputs are separated by newline*
>       if let input = input.data(using: String.Encoding.utf8) {
>         pipeIn.fileHandleForWriting.write(input)
>       }
>     }
>
>     let pipeOut = Pipe()
>     self.standardOutput = pipeOut
>
>     self.arguments = arguments
>     self.launchPath = command
>     self.currentDirectoryPath = currentDir
>
>     self.launch()
>     let output = pipeOut.fileHandleForReading.readDataToEndOfFile()
>     self.waitUntilExit()
>
>     return String(data: output, encoding: String.Encoding(rawValue: String
> .Encoding.utf8.rawValue))!
>   }
> }
>
> *//print(Process().execute(command: "/bin/ls", arguments: ["-l"]))*
>
> var cmd = Process()
>
> print("Starting...")
>
> DispatchQueue.global(qos: .default).async {
>   print("Executing...")
>   let s = cmd.execute(command: "/bin/ls", arguments: ["-l"])
>   print(s)
> }
>
> DispatchQueue.global(qos: .default).asyncAfter(deadline: DispatchTime.now()
> + .seconds(5)) {
>   if cmd.isRunning {
>     print("Terminating...")
>     cmd.terminate()
>   }
> }
>
> print("Done.")
>
>
> The code doesn't work as expected. The execute() function itself works
> fine (uncomment the call in the middle of the code), but I don't know why
> it doesn't work if it's called from within DispatchQueue closure. Even if
> I call a much more simple function —like a for loop— it doesn't work
> consistenly, sometimes the loop is completed, but other times it's not.
>
> Google didn't really help me because this topic is pretty rare I suppose.
> Could anyone enlight me, how to make the code works as I expected? What did
> I do wrong?
>
> Thank you.
>
> Regards,
>
>
> –Mr Bee
>
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