public EventArgsItemsLoaded(int aStartIndex, IList <T> aItems, ERequestPriority aRequestPriority)
: base()
{
iStartIndex = aStartIndex;
iItems = aItems;
iRequestPriority = aRequestPriority;
}
public T Item(int aIndex, ERequestPriority aPriority)
{
Assert.Check(iOpened);
Assert.Check(!iDisposed);
Assert.Check(aIndex >= 0 && aIndex < iCount);
T result = default(T);
if (!iCache.TryGet(aIndex, out result))
{
EnqueueRequest(aIndex, aPriority);
}
// readahead optimisation for foreground requests
if (aPriority == ERequestPriority.Foreground && iReadAheadRanges > 0)
{
bool ascending = aIndex >= iLastRequest;
iLastRequest = aIndex;
ReadAhead(ascending, aIndex, iReadAheadRanges);
}
return(result);
}
private void EnqueueRequest(int aIndex, ERequestPriority aPriority)
{
if (!iDisposed)
{
Assert.Check(iOpened);
Assert.Check(aIndex >= 0 && aIndex < iCount);
T item = default(T);
if (!iCache.TryGet(aIndex, out item))
{
lock (iQueueLock)
{
// get the correct start index for this request's chunk
int startIndex = iRangeSize * (aIndex / iRangeSize);
// first ensure that the request is not currently being executed
if (iExecutingRequests.ContainsKey(startIndex))
{
return;
}
// enqueue the request according to its priority (readahead requests are treated as slightly lower priority).
int insertIndex = 0;
int existingIndex = -1;
RangeRequest existingRequest = null;
for (int i = 0; i < iQueuedRequests.Count; i++)
{
RangeRequest current = iQueuedRequests[i];
if (current.Priority <= aPriority)
{
insertIndex++;
}
if (iQueuedRequests[i].StartIndex == startIndex)
{
existingIndex = i;
existingRequest = current;
}
if (existingRequest != null && current.Priority > aPriority)
{
break;
}
}
if (existingRequest != null)
{
// if it is already enqueued, but has been re-enqueued at a higher priority, move it up the queue
if (insertIndex - 1 > existingIndex)
{
existingRequest.Priority = aPriority;
iQueuedRequests.RemoveAt(existingIndex);
iQueuedRequests.Insert(insertIndex - 1, existingRequest);
}
}
else
{
Assert.Check(insertIndex <= iQueuedRequests.Count);
iQueuedRequests.Insert(insertIndex, new RangeRequest()
{
Priority = aPriority, StartIndex = startIndex
});
iDequeueScheduler.Schedule(new Scheduler.DCallback(DoDequeueRequest));
}
}
}
}
}
