private Task <Page> RequestPageLoad(string subscriptionId, long precedingCheckpoint, CancellationToken cancellationToken)
{
var loadRequest = new LoadRequest
{
SubscriptionId = subscriptionId,
PrecedingCheckpoint = precedingCheckpoint,
CancellationToken = cancellationToken
};
pendingRequests.Enqueue(loadRequest);
requestQueued.TrySetResult(true);
return(loadRequest.Page);
}
internal async Task <Page> GetNextPage(long precedingCheckpoint, string subscriptionId,
CancellationToken cancellationToken)
{
Page pageFromCache = TryGetNextPageFromCache(precedingCheckpoint, subscriptionId, cancellationToken);
if (!pageFromCache.IsEmpty)
{
if (pageFromCache.Transactions.Count < maxPageSize)
{
Task _ = RequestPageLoad(subscriptionId, pageFromCache.LastCheckpoint, cancellationToken);
}
return(pageFromCache);
}
LoadRequest pendingRequest =
pendingRequests.ToArray().SingleOrDefault(x => x.PrecedingCheckpoint == precedingCheckpoint);
if (pendingRequest != null)
{
logDebug(() =>
$"Pending Request Found (subscription: {subscriptionId}, originalSubscription: " +
$"{pendingRequest.SubscriptionId}, preceding checkpoint: {precedingCheckpoint}");
return(await pendingRequest.Page);
}
Page completedPage = await RequestPageLoad(subscriptionId, precedingCheckpoint, cancellationToken);
if ((completedPage != null) && ShouldPreloadNextPage(completedPage))
{
// Ignore the result. It will become available through the queue.
Task _ = RequestPageLoad(subscriptionId, completedPage.LastCheckpoint, cancellationToken);
}
return(completedPage);
}
