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MemoryCache class needs a Clear() method by admac


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Type: Bug
ID: 723620
Opened: 2/6/2012 5:06:52 AM
Access Restriction: Public
Moderator Decision: Sent to Engineering Team for consideration
User(s) can reproduce this bug


The .NET 4 MemoryCache class in System.Runtime.Caching needs a Clear() method, to allow completely clearing the MemoryCache.Default cache. There is no such method.

You could get an enumerator and individually remove all keys, but the MSDN documentation says don't use the GetEnumerator method!

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Posted by Microsoft on 12/4/2012 at 9:23 AM
Closing this bug for now. Product team will take a look at this suggestion for future release.
Posted by Microsoft on 2/8/2012 at 3:14 PM
Thank you for the suggestion. We're tracking this internally for a future release.
Posted by MS-Moderator08 [Feedback Moderator] on 2/6/2012 at 6:51 PM
Thank you for submitting feedback on Visual Studio 2010 and .NET Framework. Your issue has been routed to the appropriate VS development team for investigation. We will contact you if we require any additional information.
Posted by MS-Moderator01 on 2/6/2012 at 5:41 AM
Thank you for your feedback, we are currently reviewing the issue you have submitted. If this issue is urgent, please contact support directly(http://support.microsoft.com)
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Posted by Thomas F. Abraham on 3/13/2014 at 12:04 PM
Here's an efficient way to clear the cache using the existing change monitoring infrastructure instead of enumeration. It also provides the flexibility to flush either the entire cache or a named subset.

// 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;
            SignaledChangeMonitor.Signaled += OnSignalRaised; // Register instance with the shared event

        public static void Signal(string name = null)
            if (Signaled != null)
                Signaled(null, new SignaledChangeEventArgs(name)); // Raise shared event to notify all subscribers

        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("Instance " + _uniqueId + " notifying cache of change.", "SignaledChangeMonitor");
                base.OnChanged(null); // Cache objects obligated to remove the entry upon change notification.

    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("DataKey" + idx.ToString(), "DataValue" + idx.ToString(), GetPolicy(idx));

            // Flush cached items associated with "NamedData" change monitors

            // Flush all cached items

        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;
Posted by admac on 2/9/2012 at 12:52 AM
--Could write code such as the following as a workaround, but the MSDN documentation says not to use enumerators in production on MemoryCache as it is a blocking call

            List<string> cacheKeys = MemoryCache.Default.Select(kvp => kvp.Key).ToList();
            foreach (string cacheKey in cacheKeys)