/// <see cref="IEventStream.DiscardUpTo"/>
public async Task <uint> DiscardUpTo(uint sequence, CancellationToken cancel = default(CancellationToken))
{
// First, try to seek forward to skip over many events at once
var skip = await Storage.SeekAsync(sequence, 0, cancel);
if (skip > Position)
{
Position = skip;
}
// Drop elements from _cache that are before the requested sequence number
while (_cache.Count > 0 && _cache.Peek().Sequence < sequence)
{
var dequeued = _cache.Dequeue();
Sequence = dequeued.Sequence;
}
// Continues until _cache contains at least one event past the target
// sequence number (or no events left)
while (_lastSequence < sequence)
{
Sequence = _lastSequence;
const int maxBytes = 1024 * 1024 * 4;
var read = await Storage.ReadAsync(Position, maxBytes, cancel);
// Reached end of stream.
if (read.Events.Count == 0)
{
_cache.Clear();
Sequence = _lastSequence;
return(Sequence);
}
Position = read.NextPosition;
// Moved past target sequence: append events to _cache
var lastReadEvent = read.Events[read.Events.Count - 1];
_lastSequence = lastReadEvent.Sequence;
if (_lastSequence >= sequence)
{
foreach (var e in read.Events)
{
if (e.Sequence >= sequence)
{
_cache.Enqueue(e);
}
else
{
Sequence = e.Sequence;
}
}
}
}
return(Sequence);
}
public async Task <long> SeekAsync(uint key, long position = 0, CancellationToken cancel = new CancellationToken())
{
var sw = Stopwatch.StartNew();
try
{
return(await Inner.SeekAsync(key, position, cancel));
}
finally
{
Trace.WriteLine("SeekAsync " + sw.ElapsedMilliseconds);
}
}
public Task <long> SeekAsync(uint key, long position = 0, CancellationToken cancel = new CancellationToken()) => Wrapped.SeekAsync(key, position, cancel);