private CachedPage AddPageToCache(long pageIndex)
{
lock (locker)
{
//Make sure cache page limit is not exceeded
long maxCacheCount = CachedPageCapacity - 1;//-1 so we can insert the new page
long countToEvict = cachedPages.Count - maxCacheCount;
if (countToEvict > 0)
{
List <long> indicesToEvict = cachedPages.OrderBy(x => x.Value.RecentUseCounter).Select(y => y.Key).Take((int)countToEvict).ToList();
foreach (var indexToEvict in indicesToEvict)
{
EvictPageFromCache(indexToEvict);
}
}
CachedPage page = new CachedPage(this, pageIndex);
cachedPages.Add(pageIndex, page);
return(page);
}
}
private bool TryGetCachedPage(long pageIndex, out CachedPage cachedPage)
{
lock (locker)
{
if (CachedPageCapacity == 0)
{
cachedPage = null;
return(false);
}
if (!cachedPages.TryGetValue(pageIndex, out cachedPage))
{
//The page is not yet in cache
if (PageStorage.IsPageAllocated(pageIndex))
{
try
{
cachedPage = AddPageToCache(pageIndex);
return(true);
}
catch (OutOfMemoryException)
{
cachedPage = null;
return(false);
}
}
else
{
//The page is not allocated, cannot cache it
cachedPage = null;
return(false);
}
}
else
{
return(true);
}
}
}