public bool Handle(CacheAccess access, TKey key, ref TValue value, bool isGetOrPut)
{
bool found = ContainsKey(key);
if (!found || isGetOrPut)
{
if (!found && access == CacheAccess.Get)
{
// Failure; can't Get (key not found)
return(false);
}
if (TracksChanges())
{
Before(access, key, value);
}
try
{
var onAccess =
Policy != null ?
access == CacheAccess.Get ? Policy.OnGet :
access == CacheAccess.Set ? isGetOrPut ? Policy.OnPut : Policy.OnAdd : null : null;
if (access == CacheAccess.Get)
{
// It's a Get
value = this[key];
}
else
{
if (!isGetOrPut)
{
// It's an Add
Add(key, value);
}
else
{
// It's a Put
this[key] = value;
}
}
switch (access)
{
case CacheAccess.Get:
// It's a cache hit, so give the policy a chance
// to mutate the data if so desired (via onAccess)
// e.g., for the sake of reordering the evictables
// as a side-effect of the cache hit
// (cf. next comment in "finally{...}" clause below)
case CacheAccess.Set:
if (onAccess != null)
{
onAccess(Source, key, value);
}
break;
default:
throw new NotSupportedException(access.ToString());
}
}
finally
{
if (TracksChanges())
{
// Keep our own internal state consistent
// even if the policy happens to fail;
// the following is to keep the evictable
// key/value pairs in order;
// note that in the special case of LRU/MRU
// evictions, it's the passing of time
// that defines the order
// (see FifoCacheEviction<TKey, TValue>)
After(access, key, value);
}
}
// Success; could Get, Add, or Put
return(true);
}
// Failure; can't Add (key already in use)
return(false);
}
