Asp.net – How call a function when an item in MemoryCache will expire?

You can achieve this by using a combination of MemoryCache and a background task that periodically checks for expired keys and takes appropriate actions.

You can get an idea from this code:

using System;
using System.Threading;
using Microsoft.Extensions.Caching.Memory;

public class CacheManager
{
    private readonly IMemoryCache _memoryCache;
    private readonly Timer _timer;
    private readonly TimeSpan _expirationTime;
    private readonly TimeSpan _updateInterval;

    public CacheManager(IMemoryCache memoryCache, TimeSpan expirationTime, TimeSpan updateInterval)
    {
        _memoryCache = memoryCache;
        _expirationTime = expirationTime;
        _updateInterval = updateInterval;
        
        // Set up a timer to periodically update the cache
        _timer = new Timer(UpdateCache, null, TimeSpan.Zero, _updateInterval);
    }

    public void Set(string key, object value)
    {
        _memoryCache.Set(key, value, _expirationTime);
    }

    private void UpdateCache(object state)
    {
        // Iterate through cache entries and check if any have expired
        foreach (var cacheEntry in _memoryCache)
        {
            if (cacheEntry.Value == null)
            {
                // Handle expired key
                AlertAdmin(cacheEntry.Key);
                // Remove expired key from cache
                _memoryCache.Remove(cacheEntry.Key);
            }
        }
    }

    private void AlertAdmin(string key)
    {
        // Implement logic to alert system admin about expired key
        Console.WriteLine($"Key '{key}' has expired and was not updated.");
    }
}

• The CacheManager class manages the MemoryCache and includes a timer (_timer) that periodically checks for expired keys and updates them.
• When you set a value using the Set method, it sets the key-value pair in the MemoryCache with the specified expiration time.
• The UpdateCache method is called periodically by the timer. It iterates through all cache entries, checks if any have expired, alerts the system admin about expired keys, and removes them from the cache.
• You can create an instance of CacheManager and use its Set method to set keys and values in the cache. The cache entries will be automatically updated and expired keys will be handled according to your logic in the AlertAdmin method.

You can adjust the expiration time and update interval according to your requirements. Additionally, you may need to handle concurrency and synchronization if multiple threads are accessing the cache concurrently.