我使用 MemoryCache 类创建了一个缓存。我向其中添加了一些项目，但是当我需要重新加载缓存时，我想先清除它。最快的方法是什么？我应该遍历所有项目并一次删除它们还是有更好的方法？
DisposeMemoryCache.GetEnumerator() 备注部分警告：“检索 MemoryCache 实例的枚举器是一项资源密集型且阻塞的操作。因此，不应在生产应用程序中使用枚举器。”
原因如下，在 GetEnumerator() 实现的伪代码中进行了解释：
Create a new Dictionary object (let's call it AllCache)
For Each per-processor segment in the cache (one Dictionary object per processor)
{
Lock the segment/Dictionary (using lock construct)
Iterate through the segment/Dictionary and add each name/value pair one-by-one
to the AllCache Dictionary (using references to the original MemoryCacheKey
and MemoryCacheEntry objects)
}
Create and return an enumerator on the AllCache Dictionary
由于该实现将缓存拆分为多个 Dictionary 对象，因此它必须将所有内容合并到一个集合中，以便交回枚举器。每次调用 GetEnumerator 都会执行上面详述的完整复制过程。新创建的字典包含对原始内部键和值对象的引用，因此您的实际缓存数据值不会重复。
文档中的警告是正确的。避免使用 GetEnumerator() —— 包括上面所有使用 LINQ 查询的答案。
更好、更灵活的解决方案
// By Thomas F. Abraham (http://www.tfabraham.com)
namespace CacheTest
{
using System;
using System.Diagnostics;
using System.Globalization;
using System.Runtime.Caching;
public class SignaledChangeEventArgs : EventArgs
{
public string Name { get; private set; }
public SignaledChangeEventArgs(string name = null) { this.Name = name; }
}
/// <summary>
/// Cache change monitor that allows an app to fire a change notification
/// to all associated cache items.
/// </summary>
public class SignaledChangeMonitor : ChangeMonitor
{
// Shared across all SignaledChangeMonitors in the AppDomain
private static event EventHandler<SignaledChangeEventArgs> Signaled;
private string _name;
private string _uniqueId = Guid.NewGuid().ToString("N", CultureInfo.InvariantCulture);
public override string UniqueId
{
get { return _uniqueId; }
}
public SignaledChangeMonitor(string name = null)
{
_name = name;
// Register instance with the shared event
SignaledChangeMonitor.Signaled += OnSignalRaised;
base.InitializationComplete();
}
public static void Signal(string name = null)
{
if (Signaled != null)
{
// Raise shared event to notify all subscribers
Signaled(null, new SignaledChangeEventArgs(name));
}
}
protected override void Dispose(bool disposing)
{
SignaledChangeMonitor.Signaled -= OnSignalRaised;
}
private void OnSignalRaised(object sender, SignaledChangeEventArgs e)
{
if (string.IsNullOrWhiteSpace(e.Name) || string.Compare(e.Name, _name, true) == 0)
{
Debug.WriteLine(
_uniqueId + " notifying cache of change.", "SignaledChangeMonitor");
// Cache objects are obligated to remove entry upon change notification.
base.OnChanged(null);
}
}
}
public static class CacheTester
{
public static void TestCache()
{
MemoryCache cache = MemoryCache.Default;
// Add data to cache
for (int idx = 0; idx < 50; idx++)
{
cache.Add("Key" + idx.ToString(), "Value" + idx.ToString(), GetPolicy(idx));
}
// Flush cached items associated with "NamedData" change monitors
SignaledChangeMonitor.Signal("NamedData");
// Flush all cached items
SignaledChangeMonitor.Signal();
}
private static CacheItemPolicy GetPolicy(int idx)
{
string name = (idx % 2 == 0) ? null : "NamedData";
CacheItemPolicy cip = new CacheItemPolicy();
cip.AbsoluteExpiration = System.DateTimeOffset.UtcNow.AddHours(1);
cip.ChangeMonitors.Add(new SignaledChangeMonitor(name));
return cip;
}
}
}
var cacheItems = cache.ToList();
foreach (KeyValuePair<String, Object> a in cacheItems)
{
cache.Remove(a.Key);
}
cache.ToList().ForEach(a => cache.Remove(a.Key));
Trim的方法。
所以要清除所有内容，你只需要做
cache.Trim(100)
编辑： 深入研究后，似乎不值得花时间去研究 Trim
https://connect.microsoft.com/VisualStudio/feedback/details/831755/memorycache-trim-method-doesnt-evict-100-of-the-items
public void ClearAll()
{
var allKeys = _cache.Select(o => o.Key);
Parallel.ForEach(allKeys, key => _cache.Remove(key));
}
Dim _Qry = (From n In CacheObject.AsParallel()
Select n).ToList()
For Each i In _Qry
CacheObject.Remove(i.Key)
Next
var field = typeof(MemoryCache).GetField("s_defaultCache",
BindingFlags.Static |
BindingFlags.NonPublic);
field.SetValue(null, null);
var cache = GlobalCachingProvider.Instance.GetAllItems();
if (dbOperation.SuccessLoadingAllCacheToDB(cache))
{
cache.Clear();
}
var cacheKeys = MemoryCache.Default.Where(kvp.Value is MyType).Select(kvp => kvp.Key).ToList();
foreach (string cacheKey in cacheKeys)
{
MemoryCache.Default.Remove(cacheKey);
}
https://learn.microsoft.com/en-us/answers/answers/983399/view.html
我在那里写了一个答案，我将在这里转录：
using System.Collections.Generic;
using Microsoft.Extensions.Caching.Memory;
using ServiceStack;
public static class IMemoryCacheExtensions
{
static readonly List<object> entries = new();
/// <summary>
/// Removes all entries, added via the "TryGetValueExtension()" method
/// </summary>
/// <param name="cache"></param>
public static void Clear(this IMemoryCache cache)
{
for (int i = 0; i < entries.Count; i++)
{
cache.Remove(entries[i]);
}
entries.Clear();
}
/// <summary>
/// Use this extension method, to be able to remove all your entries later using "Clear()" method
/// </summary>
/// <typeparam name="TItem"></typeparam>
/// <param name="cache"></param>
/// <param name="key"></param>
/// <param name="value"></param>
/// <returns></returns>
public static bool TryGetValueExtension<TItem>(this IMemoryCache cache, object key, out TItem value)
{
entries.AddIfNotExists(key);
if (cache.TryGetValue(key, out object result))
{
if (result == null)
{
value = default;
return true;
}
if (result is TItem item)
{
value = item;
return true;
}
}
value = default;
return false;
}
}
private readonly IMemoryCache _memoryCache;
public AdminController(IMemoryCache memoryCache)
{
_memoryCache = memoryCache;
}
[HttpGet("ClearCache")]
public IActionResult ClearCache()
{
ClearMemoryCache();
return Ok();
}
private void ClearMemoryCache()
{
var cacheImplType = typeof(MemoryCache);
var entriesField = cacheImplType.GetField("_entries", BindingFlags.NonPublic | BindingFlags.Instance);
var entries = (IDictionary)entriesField?.GetValue(_memoryCache);
entries?.Clear();
}
它对我有用。