/// <summary>
/// Catch up with the stream (updating the state) until there are no new
/// events available.
/// </summary>
public async Task CatchUpAsync(CancellationToken cancel = default)
{
Func <bool> finishFetch;
// Local variable, to avoid reaching the limit when not doing the
// initial catch-up.
var eventsSinceLastCacheLoad = 0u;
do
{
var fetchTask = Stream.BackgroundFetchAsync(cancel);
// We have started fetching the next batch of events in
// the background, so we might as well start processing
// those we already have. This pattern is optimized for
// when fetching events takes longer than processing them,
// and remains safe (i.e. no runaway memory usage) when
// the reverse is true.
eventsSinceLastCacheLoad += CatchUpLocal();
// Maybe we have reached the event count limit before our
// save/load cycle ?
if (eventsSinceLastCacheLoad >= EventsBetweenCacheSaves)
{
eventsSinceLastCacheLoad = 0;
var sw = Stopwatch.StartNew();
if (await _projection.TrySaveAsync(cancel))
{
// Reset first, to release any used memory.
_projection.Reset();
await _projection.TryLoadAsync(cancel);
if (_projection.Sequence != Stream.Sequence)
{
throw new InvalidOperationException(
"Projection Save/Load cycle failed to restore sequence.");
}
_log.Info($"[ES read] cache save/load cycle in {sw.Elapsed} at seq {_projection.Sequence}.");
}
}
finishFetch = await fetchTask;
} while (finishFetch());
// We reach this point if 1° all events cached in the stream have
// been processed and 2° the fetch operation returned no new events
NotifyRefresh();
}
/// <summary> Attempt to save the projection to the cache. </summary>
/// <remarks>
/// While this returns a task, the save operation itself does not touch the
/// object (only an immutable copy of the state), so you do not need to
/// wait for this task to finish before starting another operation.
/// </remarks>
public Task TrySaveAsync(CancellationToken cancel = default(CancellationToken))
{
return(_projection.TrySaveAsync(cancel));
}
/// <summary> Attempt to save the projection to the cache. </summary> /// <remarks> /// While this returns a task, the save operation itself does not touch the /// object (only an immutable copy of the state), so you do not need to /// wait for this task to finish before starting another operation. /// </remarks> public Task TrySaveAsync(CancellationToken cancel = default) => _projection.TrySaveAsync(cancel);