/// <summary>
/// Safely changes the current state
/// </summary>
/// <param name="newState">New state</param>
/// <param name="prevState">Previously observed state</param>
/// <returns>Was state changed (false means that the state transition is not valid)</returns>
private bool ChangeStateSafe(QueueAsyncProcessorState newState, out QueueAsyncProcessorState prevState)
{
prevState = (QueueAsyncProcessorState)Volatile.Read(ref _state);
if (!IsValidStateTransition(prevState, newState))
{
return(false);
}
SpinWait sw = new SpinWait();
while (Interlocked.CompareExchange(ref _state, (int)newState, (int)prevState) != (int)prevState)
{
sw.SpinOnce();
prevState = (QueueAsyncProcessorState)Volatile.Read(ref _state);
if (!IsValidStateTransition(prevState, newState))
{
return(false);
}
}
return(true);
}
/// <summary>
/// Verifies that state transition is possible
/// </summary>
/// <param name="oldState">Current state</param>
/// <param name="newState">New state</param>
/// <returns>True when state transition can be performed</returns>
private bool IsValidStateTransition(QueueAsyncProcessorState oldState, QueueAsyncProcessorState newState)
{
switch (oldState)
{
case QueueAsyncProcessorState.Created:
return(newState == QueueAsyncProcessorState.StartRequested || newState == QueueAsyncProcessorState.StopRequested);
case QueueAsyncProcessorState.StartRequested:
return(newState == QueueAsyncProcessorState.Running || newState == QueueAsyncProcessorState.Stopped);
case QueueAsyncProcessorState.Running:
return(newState == QueueAsyncProcessorState.StopRequested);
case QueueAsyncProcessorState.StopRequested:
return(newState == QueueAsyncProcessorState.Stopped);
case QueueAsyncProcessorState.Stopped:
return(false);
default:
return(false);
}
}