public async Task <List <E> > ListenAsync <E>(object listenId, Func <IQueryable <E>, IQueryable <E> > filter, TimeSpan maxWait, CancellationToken token) where E : EntityBase
{
logger.LogTrace($"ListenNewAsync called for maxWait {maxWait}");
using (CancellationTokenSource linkedCts = CancellationTokenSource.CreateLinkedTokenSource(token))
{
//We MUST start listening FIRST so we DON'T miss anything AT ALL (we could miss valuable signals that occur while reading initially)
var listener = signaler.ListenAsync(listenId, q => filter(q.Where(e => e is E).Cast <E>()), maxWait, linkedCts.Token);
DateTime start = DateTime.Now; //Putting this down here to minimize startup time before listen (not that this little variable really matters)
var baseE = await query.GetQueryableAsync <E>();
var results = await LockAsync(() => query.GetListAsync(filter(baseE.Select(x => (E)x))));
if (results.Count > 0)
{
linkedCts.Cancel();
try
{
//Yes, we are so confident that we don't even worry about waiting properly
await listener;
}
catch (OperationCanceledException) {} //This is expected
return(results);
}
else
{
return((await listener).Cast <E>().ToList());
}
}
}
