SubProcess.swift

import Darwin.C
import Venice

struct SubProcess {

    let path: String
    let arguments: [String]

    func run(sync sync: Bool = true) -> Int? {

        let childPID = fork()

        switch childPID {
        case -1: // error
            return nil
        case 0: // child
            let executable = path.characters.split("/").last?.map { String($0) }.joinWithSeparator("") ?? ""

            let args = ([executable] + arguments).map { $0.withCString(strdup) } + [nil] // null terminated

            execv(path, args)

            fatalError("The execv function failed and did not overwrite child process's memory successfully. (errno: \(errno))")

        default: // parent
            if sync { waitpid(childPID, nil, 0) } // blocks until child exits
            else { signal(SIGCHLD, SIG_IGN) } // ignore child signal
            return Int(childPID)
        }
    }
}


let sp = SubProcess(path: "/bin/echo", arguments: ["hello", "world"])

// launch 3 child processes (which prints "hello world" 3 times)
for i in 1...3 {
  sp.run(sync: false)
  print("launched \(i)")
}