/// <summary>
/// Enforces behaviour required for logging unsuccessful cache requests and providing implementation-independent checks, so that the plugin author
/// doesn't need to remember to call Request[Succeeded|Failed] or do general checks. Plugin author provides implementation-specific caching in
/// the 'DoGetChunk' function.
/// </summary>
/// <param name="listener"></param>
/// <param name="cancellationToken"></param>
/// <returns></returns>
public virtual T GetChunk(IDataLoadEventListener listener, GracefulCancellationToken cancellationToken)
{
Request = RequestProvider.GetNext(listener);
// If GetNext returns null, there are no further failures to process and we're done
if (Request == null)
{
listener.OnNotify(this, new NotifyEventArgs(ProgressEventType.Information, "The RequestProvider has no more requests to provide (RequestProvider.GetNext returned null)"));
return(null);
}
if (Request.CacheProgress == null)
{
throw new InvalidOperationException("The request has no CacheProgress item (in this case to determine when the lag period begins)");
}
// Check if we will stray into the lag period with this fetch and if so signal we are finished
var cacheLagPeriod = Request.CacheProgress.GetCacheLagPeriod();
if (cacheLagPeriod != null && cacheLagPeriod.TimeIsWithinPeriod(Request.End))
{
listener.OnNotify(this, new NotifyEventArgs(ProgressEventType.Information, "The Request is for a time within the Cache Lag Period. This means we are up-to-date and can stop now."));
return(null);
}
Chunk = DoGetChunk(Request, listener, cancellationToken);
if (Chunk != null && Chunk.Request == null && Request != null)
{
listener.OnNotify(this,
new NotifyEventArgs(ProgressEventType.Error,
"DoGetChunk completed and set a Chunk Successfully but the Chunk.Request was null. Try respecting the Request property in your class when creating your Chunk."));
}
return(Chunk);
}
