我个人致力于 .net 分布式缓存解决方案，但我认为这个问题在所有平台上都很有趣。
是否有分布式缓存解决方案（或通用策略）允许在缓存中存储对象同时保持它们之间引用的完整性？
举例说明 - 假设我有一个对象 Foo foo 引用了一个对象 Bar bar，还有一个对象 Foo foo2 引用了相同的 Bar bar。如果我将foo 加载到缓存中，则bar 的副本将与它一起存储。如果我还将foo2 加载到缓存中，则会同时存储bar 的单独副本。如果我在缓存中更改foo.bar，更改不会影响foo2.bar :(
是否有现有的分布式缓存解决方案可以让我将foo、foo2 和bar 加载到缓存中，同时保持foo.bar foo2.bar 引用？
【问题讨论】：
首先
我不知道任何分布式系统，并且我不假装构建一个。这篇文章解释了如何使用带有可序列化对象的 IObjectReference 接口在 .NET 和 C# 中模拟这种行为。
现在，让我们继续表演吧
我不知道这样的分布式系统，但您可以使用 .NET 使用 IObjectReference 接口轻松实现这一目标。您对ISerializable.GetObjectData 的实现需要调用SerializationInfo.SetType 来指出一个实现IObjectReference 的代理类，并且能够（在您的GetObjectData 方法提供的数据的帮助下）获得对应该使用的真实对象的引用.
示例代码：
[Serializable]
internal sealed class SerializationProxy<TOwner, TKey> : ISerializable, IObjectReference {
private const string KeyName = "Key";
private const string InstantiatorName = "Instantiator";
private static readonly Type thisType = typeof(SerializationProxy<TOwner, TKey>);
private static readonly Type keyType = typeof(TKey);
private static readonly Type instantiatorType = typeof(Func<TKey, TOwner>);
private readonly Func<TKey, TOwner> _instantiator;
private readonly TKey _key;
private SerializationProxy() {
}
private SerializationProxy(SerializationInfo info, StreamingContext context) {
if (info == null) throw new ArgumentNullException("info");
_key = (TKey)info.GetValue(KeyName, keyType);
_instantiator = (Func<TKey, TOwner>)info.GetValue(InstantiatorName, instantiatorType);
}
void ISerializable.GetObjectData(SerializationInfo info, StreamingContext context) {
throw new NotSupportedException("This type should never be serialized.");
}
object IObjectReference.GetRealObject(StreamingContext context) {
return _instantiator(_key);
}
internal static void PrepareSerialization(SerializationInfo info, TKey key, Func<TKey, TOwner> instantiator) {
if (info == null) throw new ArgumentNullException("info");
if (instantiator == null) throw new ArgumentNullException("instantiator");
info.SetType(thisType);
info.AddValue(KeyName, key, keyType);
info.AddValue(InstantiatorName, instantiator, instantiatorType);
}
}
此代码将从您的 GetObjectData 方法中使用 SerializationProxy.PrepareSerialization(info, myKey, myKey => LoadedInstances.GetById(myKey)) 调用，并且您的 LoadedInstances.GetById 应该从 Dictionary
编辑：
我写了一些示例代码来说明我的意思。
public static class Program {
public static void Main() {
// Create an item and serialize it.
// Pretend that the bytes are stored in some magical
// domain where everyone lives happily ever after.
var item = new Item { Name = "Bleh" };
var bytes = Serialize(item);
{
// Deserialize those bytes back into the cruel world.
var loadedItem1 = Deserialize<Item>(bytes);
var loadedItem2 = Deserialize<Item>(bytes);
// This should work since we've deserialized identical
// data twice.
Debug.Assert(loadedItem1.Id == loadedItem2.Id);
Debug.Assert(loadedItem1.Name == loadedItem2.Name);
// Notice that both variables refer to the same object.
Debug.Assert(ReferenceEquals(loadedItem1, loadedItem2));
loadedItem1.Name = "Bluh";
Debug.Assert(loadedItem1.Name == loadedItem2.Name);
}
{
// Deserialize those bytes back into the cruel world. (Once again.)
var loadedItem1 = Deserialize<Item>(bytes);
// Notice that we got the same item that we messed
// around with earlier.
Debug.Assert(loadedItem1.Name == "Bluh");
// Once again, force the peaceful object to hide its
// identity, and take on a fake name.
loadedItem1.Name = "Blargh";
var loadedItem2 = Deserialize<Item>(bytes);
Debug.Assert(loadedItem1.Name == loadedItem2.Name);
}
}
#region Serialization helpers
private static readonly IFormatter _formatter
= new BinaryFormatter();
public static byte[] Serialize(ISerializable item) {
using (var stream = new MemoryStream()) {
_formatter.Serialize(stream, item);
return stream.ToArray();
}
}
public static T Deserialize<T>(Byte[] bytes) {
using (var stream = new MemoryStream(bytes)) {
return (T)_formatter.Deserialize(stream);
}
}
#endregion
}
// Supercalifragilisticexpialidocious interface.
public interface IDomainObject {
Guid Id { get; }
}
// Holds all loaded instances using weak references, allowing
// the almighty garbage collector to grab our stuff at any time.
// I have no real data to lend on here, but I _presume_ that this
// wont be to overly evil since we use weak references.
public static class LoadedInstances<T>
where T : class, IDomainObject {
private static readonly Dictionary<Guid, WeakReference> _items
= new Dictionary<Guid, WeakReference>();
public static void Set(T item) {
var itemId = item.Id;
if (_items.ContainsKey(itemId))
_items.Remove(itemId);
_items.Add(itemId, new WeakReference(item));
}
public static T Get(Guid id) {
if (_items.ContainsKey(id)) {
var itemRef = _items[id];
return (T)itemRef.Target;
}
return null;
}
}
[DebuggerDisplay("{Id} {Name}")]
[Serializable]
public class Item : IDomainObject, ISerializable {
public Guid Id { get; private set; }
public String Name { get; set; }
// This constructor can be avoided if you have a
// static Create method that creates and saves new items.
public Item() {
Id = Guid.NewGuid();
LoadedInstances<Item>.Set(this);
}
#region ISerializable Members
public void GetObjectData(SerializationInfo info, StreamingContext context) {
// We're calling SerializationProxy to call GetById(this.Id)
// when we should be deserialized. Notice that we have no
// deserialization constructor. Fxcop will hate us for that.
SerializationProxy<Item, Guid>.PrepareSerialization(info, Id, GetById);
}
#endregion
public static Item GetById(Guid id) {
var alreadyLoaded = LoadedInstances<Item>.Get(id);
if (alreadyLoaded != null)
return alreadyLoaded;
// TODO: Load from storage container (database, cache).
// TODO: The item we load should be passed to LoadedInstances<Item>.Set
return null;
}
}
【讨论】：