Grabs a lock and ensures mutual exclusion in swift

synced.swift

/**
 * Grabs a lock and ensures mutual exclusion while calling `closure`
 *  Example: 
 * synced(self) {
 *    // Code
 * }
 */
func synced(lock: AnyObject, closure: () -> ()) {
  objc_sync_enter(lock)
  closure()
  objc_sync_exit(lock)
}