public void AddOrAccess(T item, IWeakAction <T> evictor)
{
Contract.ThrowIfNull(evictor);
// move up cost upper bound by fixed increase amount.
Interlocked.Add(ref this.currentCostUpperBound, this.fixedIncrementAmount);
// check whether it already exist. we do this here since we don't want to
// create new CacheEntry unnecessarily
CacheEntry existingEntry;
var existed = this.items.TryGetValue(item, out existingEntry);
// cache miss
if (!existed)
{
// try add - could have been added by other threads
var newCacheEntry = new CacheEntry(CacheId.NextItemId(), evictor);
existingEntry = this.items.AddOrUpdate(item, newCacheEntry, updateCacheEntry);
// it was already cached by other thread
existed = newCacheEntry != existingEntry;
}
else
{
// there is a race here. entry might have been kicked out from the cache and we are changing a
// stale one. the race could introduce a situation where an item that has been chosen for eviction by one thread
// is being accessed here. that's unfortunate, but I feel it's acceptable.
UpdateCacheEntry(item, existingEntry);
}
CreateEvictionTaskIfNecessary();
Logger.Log(FeatureId.Cache, FunctionId.Cache_AddOrAccess, logAddOrAccessed, existingEntry.ItemId, item, existed);
}
protected CostBasedCache(
IOptionService optionService,
int minCount, long minCost, long maxCost,
double coolingRate, int fixedIncAmount, TimeSpan dataCollectionTimeSpan,
Func <T, long> costCalculator,
bool eagarlyEvict,
Func <T, string> uniqueIdGetter)
{
// set cache id for this cache
this.cacheId = CacheId.NextCacheId();
// log all variables used to create the cache. this should be called only once. should be okay to allocate the string.
Logger.Log(FunctionId.Cache_Created, string.Join(",", cacheId, typeof(T), minCount, minCost, maxCost, coolingRate, fixedIncAmount, dataCollectionTimeSpan.TotalMilliseconds));
this.minCount = minCount;
this.minCost = minCost;
this.maxCost = maxCost;
this.fixedIncrementAmount = fixedIncAmount;
this.coolingRate = coolingRate;
this.dataCollectionBufferInMS = (int)dataCollectionTimeSpan.TotalMilliseconds;
this.costCalculator = costCalculator;
this.uniqueIdGetter = uniqueIdGetter;
this.eagarlyEvict = eagarlyEvict;
this.updateCacheEntry = UpdateCacheEntry;
this.logAddOrAccessed = LogAddOrAccessed;
this.logEvictedOrRemoved = LogEvictedOrRemoved;
this.comparer = Comparer;
// use environment tick here which is known to be the least expensive one to get and low
// but good enough accuracy for the cache (15ms on most of system)
this.lastTimeTaskRan = Environment.TickCount;
// set base cost
this.currentCostUpperBound = minCost;
this.rankGetter = RankingAlgorithm;
// respond to option change
this.optionService = optionService;
this.optionService.OptionChanged += OnOptionChanged;
}
