/// <summary>
/// Reads up events up to the last one available. Pre-loads the projection from its cache,
/// if available, to reduce the necessary work.
/// </summary>
public async Task InitializeAsync(CancellationToken cancel = default(CancellationToken))
{
var sw = Stopwatch.StartNew();
try
{
// Load project and discard events before that.
_log?.Info($"{sw.Elapsed:mm':'ss'.'ff} [ES init] loading projections.");
await _projection.TryLoadAsync(cancel).ConfigureAwait(false);
var catchUp = _projection.Sequence + 1;
if (_onEachCommitted != null)
{
foreach (var e in _onEachCommitted)
{
if (e.Start < catchUp)
{
catchUp = e.Start;
}
}
}
_log?.Info($"{sw.Elapsed:mm':'ss'.'ff} [ES init] advancing stream to seq {catchUp}.");
await Stream.DiscardUpTo(catchUp, cancel).ConfigureAwait(false);
if (Stream.Sequence < catchUp)
{
_log?.Warning(
$"{sw.Elapsed:mm':'ss'.'ff} [ES init] invalid seq {catchUp} > {Stream.Sequence}, resetting everything.");
// Cache is apparently beyond the available sequence. Could happen in
// development environments with non-persistent events but persistent
// caches. Treat cache as invalid and start from the beginning.
Stream.Reset();
_projection.Reset();
}
}
catch (Exception e)
{
_log?.Warning(
$"{sw.Elapsed:mm':'ss'.'ff} [ES init] error while reading cache.", e);
// Something went wrong when reading the cache. Stop.
Stream.Reset();
_projection.Reset();
}
// Start reading everything
_log?.Info($"{sw.Elapsed:mm':'ss'.'ff} [ES init] catching up with stream.");
await CatchUpAsync(cancel).ConfigureAwait(false);
_log?.Info($"{sw.Elapsed:mm':'ss'.'ff} [ES init] DONE !");
}
/// <summary>
/// Catch up with the stream (updating the state) until there are no new
/// events available.
/// </summary>
public async Task CatchUpAsync(CancellationToken cancel = default)
{
Func <bool> finishFetch;
// Local variable, to avoid reaching the limit when not doing the
// initial catch-up.
var eventsSinceLastCacheLoad = 0u;
do
{
var fetchTask = Stream.BackgroundFetchAsync(cancel);
// We have started fetching the next batch of events in
// the background, so we might as well start processing
// those we already have. This pattern is optimized for
// when fetching events takes longer than processing them,
// and remains safe (i.e. no runaway memory usage) when
// the reverse is true.
eventsSinceLastCacheLoad += CatchUpLocal();
// Maybe we have reached the event count limit before our
// save/load cycle ?
if (eventsSinceLastCacheLoad >= EventsBetweenCacheSaves)
{
eventsSinceLastCacheLoad = 0;
var sw = Stopwatch.StartNew();
if (await _projection.TrySaveAsync(cancel))
{
// Reset first, to release any used memory.
_projection.Reset();
await _projection.TryLoadAsync(cancel);
if (_projection.Sequence != Stream.Sequence)
{
throw new InvalidOperationException(
"Projection Save/Load cycle failed to restore sequence.");
}
_log.Info($"[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();
}
public void multi_apply_reset()
{
var reified = new ReifiedProjectionGroup <int, State>(new IProjection <int>[]
{
MockInteger().Object,
MockString().Object
});
reified.Apply(1U, 10);
Assert.IsNotNull(reified.Current);
reified.Reset();
Assert.AreEqual((uint)0U, (uint)reified.Sequence);
Assert.AreEqual((int)0, (int)reified.Current.I.Value);
Assert.AreEqual("I", reified.Current.S);
}
/// <summary> Reset the wrapper. Used when it is necessary to try again. </summary>
public void Reset()
{
_projection.Reset();
Stream.Reset();
}