/// <summary>
/// Event handler for polling timer. Look for new devices and remove old ones.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private static void FindDeviceTimer_Elapsed(object sender, ElapsedEventArgs e)
{
TimeSinceReCheck += QueryInterval;
if (TimeSinceReCheck - ReCheckInterval > 0)
{
TimeSinceReCheck = 0;
var enumerator = DeviceList.GetEnumerator();
while (enumerator.MoveNext())
{
var key = enumerator.Current.Key;
try
{
// If it is time to recheck devices, mark every device as not discovered
if (!DeviceList.TryUpdate(key, false, true))
{
// TryUpdate returned false.
// The device has already was not found the previous recheck cycle. Assume it is gone and notify the user.
bool ret;
if (DeviceList.TryRemove(key, out ret))
{
PrintQueue.Enqueue($"Lost: {key}");
}
}
}
catch (KeyNotFoundException) { } // Device was already removed.
}
}
// Look for new and previously discovered devices
MDns.SendQuery(ServiceToQuery);
}