[英]How is this cache manager storing the cached data?
我正在使用這個緩存管理器,取自github上的bbarry 。
我不了解實際在哪里或如何存儲緩存的數據。 我見過的大多數緩存都使用MemoryCache
,但是我在任何地方都沒有提到它。
我只能認為ConcurrentDictionary
正在存儲緩存的數據,但是如果是這樣,我不明白為什么將其設置為readonly
。
public static class Cache<T> {
static readonly ConcurrentDictionary<string, T> Dictionary = new ConcurrentDictionary<string, T>();
//by making this a tuple with the generic constraint, there will be one per cache type; the first parameter will always be the default value
static readonly ConcurrentDictionary<string, Tuple<T, DateTime, TimeSpan>> Removals = new ConcurrentDictionary<string, Tuple<T, DateTime, TimeSpan>>();
public static T GetOrAdd(string key, Func<string, T> creator) { return GetOrAdd(key, creator, null, null); }
public static T GetOrAdd(string key, Func<string, T> creator, DateTime absoluteExpiration) { return GetOrAdd(key, creator, absoluteExpiration, null); }
public static T GetOrAdd(string key, Func<string, T> creator, TimeSpan slidingExpiration) { return GetOrAdd(key, creator, null, slidingExpiration); }
public static bool TryGetValue(string key, out T value) {
Tuple<T, DateTime, TimeSpan> when;
if (Removals.TryGetValue(key, out when) && when.Item3 != TimeSpan.Zero) {
Remove(key, Tuple.Create(default(T), DateTime.Now.Add(when.Item3), when.Item3));
}
return Dictionary.TryGetValue(key, out value);
}
public static bool Expire(string key, out T value) { return Dictionary.TryRemove(key, out value); }
public static void Expire(string key) {
T value;
Dictionary.TryRemove(key, out value);
}
static T GetOrAdd(string key, Func<string, T> creator, DateTime? absoluteExpiration, TimeSpan? slidingExpiration) {
if (key == null) {
throw new ArgumentNullException("key");
}
Tuple<T, DateTime, TimeSpan> when;
var updateRemoval = Removals.TryGetValue(key, out when) && when.Item3 != TimeSpan.Zero;
var v = Dictionary.GetOrAdd(key, creator);
if (absoluteExpiration == null && slidingExpiration == null && !updateRemoval) {
return v;
}
if (absoluteExpiration != null || slidingExpiration != null) {
var expiration = (TimeSpan)(slidingExpiration ?? (absoluteExpiration - DateTime.Now));
when = Tuple.Create(default(T), DateTime.Now.Add(expiration), expiration);
} else {
when = Tuple.Create(default(T), DateTime.Now.Add(when.Item3), when.Item3);
}
if (absoluteExpiration != null) {
Removals.TryAdd(key, Tuple.Create(default(T), (DateTime)absoluteExpiration, TimeSpan.Zero));
} else {
Removals.AddOrUpdate(key, when, (a, b) => when);
}
Remove(key, when);
return v;
}
static void Remove(string key, Tuple<T, DateTime, TimeSpan> then) {
System.Threading.Tasks.Task.Delay(then.Item3).ContinueWith(task => {
Tuple<T, DateTime, TimeSpan> when;
if (!Removals.TryGetValue(key, out when) || when.Item2 >= DateTime.Now)
return;
T v;
Dictionary.TryRemove(key, out v);
Removals.TryRemove(key, out when);
});
}
}
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