private static void PingAll(IEnumerable<System.Tuple<IPAddress, string>> hosts, Action<IEnumerable<string>> completion)

        {

            if (completion == null) throw new ArgumentNullException("completion");

            if (hosts == null || !hosts.Any()) completion(Enumerable.Empty<string>());

​

            ThreadPool.QueueUserWorkItem(delegate

            {

                var waiters = new List<ManualResetEvent>();

                var onlineHosts = new List<string>();

                try

                {

                    using (var ping = new Ping())

                    {

                        ping.PingCompleted += (sender, args) =>

                        {

                            var state = (System.Tuple<string, ManualResetEvent>) args.UserState;

                            try

                            {

                                if (args.Reply.Status == IPStatus.Success)

                                {

                                    lock (onlineHosts) onlineHosts.Add(state.Item1);

                                }

                            }

                            finally

                            {

                                try

                                {

                                    state.Item2.Set();

                                }

                                catch

                                {

                                    // do nothing

                                }

                            }

                        };

​

                        foreach (var host in hosts)

                        {

                            var mre = new ManualResetEvent(false);

                            var token = new System.Tuple<string, ManualResetEvent>(host.Item2, mre);

                            ping.SendAsync(host.Item1, 1000,new[] {(byte) 'P', (byte) 'i', (byte) 'n', (byte) 'g'}, token);

                            waiters.Add(new ManualResetEvent(false));

                        }

​

                        foreach (var w in waiters)

                        {

                            w.WaitOne();

                        }

​

                        completion(onlineHosts);

                    }

                }

                catch (Exception)

                {

                    completion(Enumerable.Empty<string>());

                }

                finally

                {

                    foreach (var w in waiters)

                    {

                        try

                        {

                            w.Close();

                        }

                        catch

                        {

                            // do nothing

                        }

                    }

                }

​

            });

        }