Signal handling in Swift

handle-signal.swift

/**
http://rosettacode.org/wiki/Handle_a_signal

Most general purpose operating systems provide interrupt facilities, sometimes called signals. 
Unhandled signals generally terminate a program in a disorderly manner. Signal handlers are 
created so that the program behaves in a well-defined manner upon receipt of a signal.

For this task you will provide a program that displays a single integer on each line of output at 
the rate of one integer in each half second. Upon receipt of the SigInt signal (often created by the user typing ctrl-C) 
the program will cease printing integers to its output, print the number of seconds the program has run, 
and then the program will terminate.
*/

import Foundation

let startTime = NSDate()
var signalReceived: sig_atomic_t = 0

signal(SIGINT) { signal in signalReceived = 1 }

for var i = 0;; {
    if signalReceived == 1 { break }
    usleep(500_000)
    if signalReceived == 1 { break }
    print(++i)
}

let endTime = NSDate()
print("Program has run for \(endTime.timeIntervalSinceDate(startTime)) seconds")

Setting a flag and testing it within the "for" of the program is not a good way to use trap.

If the code in the for is in a loop, it will never come out to encounter the break