/* After a successful call, the resources necessary to perform the operation
* should be reserved for the time of the returned authorization. */
public RequestResult RequestLanding(Guid aircraftId)
{
mutex.WaitOne();
// A runway and a parking stand are available.
if (NumberOfAvailableRunways() > 0 && NumberOfAvailableParkingStands() > 0)
{
// Reserve and return the resources' ids
Guid runwayId = ReserveAvailableRunway();
Guid parkingStandId = ReserveAvailableParkingStand();
// Create the landing request token
LandingRequestToken token = new LandingRequestToken(TokenValiditySeconds, aircraftId, runwayId, parkingStandId);
// Subscribe for token's expiration to ensure reserved resources can be released.
token.Elapsed += OnExpiredLandingToken;
mutex.ReleaseMutex();
return(new RequestResult(RequestResult.RequestState.Proceed, token));
}
else
{
mutex.ReleaseMutex();
return(new RequestResult(RequestResult.RequestState.Hold, null));
}
}
// Releases resources when the landing token's timer elapses.
private void OnExpiredLandingToken(object source, ElapsedEventArgs e)
{
LandingRequestToken token = (LandingRequestToken)source;
// Unsubscribe from the token's timer.
token.Elapsed -= OnExpiredLandingToken;
// Release the token's resources.
ReleaseLandingResources(token);
}
// Release resources reserved by a landing request token that will not be used.
private void ReleaseLandingResources(LandingRequestToken token)
{
Runway runway = GetRunwayById(token.runwayId);
ParkingStand parkingStand = GetParkingStandById(token.parkingStandId);
runway.state = Runway.RunwayState.Available;
runway.aircraftId = Guid.Empty;
parkingStand.aircraftId = Guid.Empty;
parkingStand.state = ParkingStand.ParkingStandState.Available;
token.Dispose();
}
/* After this call is executed successfully, the used runway is InOperation
* for the length of operation duration parameter and can't handle any other
* operations during this time. After the operation is completed, the runway
* becomes Available again, and the reserved parking stand becomes
* Occupied. The call is non-blocking, i.e. it returns before the runway is
* cleared. */
public PerformResult PerformLanding(LandingRequestToken token)
{
token.Stop();
token.Elapsed -= OnExpiredLandingToken;
// Token hasn't expired yet
if (DateTime.Now <= token.expiration && !token.hasExpired)
{
Runway runway = GetRunwayById(token.runwayId);
// Check if the runway exists and if it has been properly reserved
if (runway == null || runway.state != Runway.RunwayState.Reserved)
{
ReleaseLandingResources(token);
return(PerformResult.InvalidParameters);
}
ParkingStand parkingStand = GetParkingStandById(token.parkingStandId);
// Check if the parkingStand exists and if it has been properly reserved
if (parkingStand == null || parkingStand.state != ParkingStand.ParkingStandState.Reserved)
{
ReleaseLandingResources(token);
return(PerformResult.InvalidParameters);
}
runway.aircraftId = token.aircraftId;
parkingStand.aircraftId = runway.aircraftId;
runway.Elapsed += OnLandingOperationComplete;
token.Dispose();
runway.Operate();
return(PerformResult.Success);
}
else // Token has expired
{
if (!token.hasExpired) // the token's expiration date has passed but the elapsed event hasn't fired yet, then release the resources.
{
ReleaseLandingResources(token);
}
return(PerformResult.ExpiredToken);
}
}
