Develop Reference

Looking for a way to do less locking while caching

I am using the code below to cache items. It's pretty basic.
The issue I have is that every time it caches an item, section of the code locks. So with roughly a million items arriving every hour or so, this is a problem.
I've tried creating a dictionary of static lock objects per cacheKey, so that locking is granular, but that in itself becomes an issue with managing expiration of them, etc...
Is there a better way to implement minimal locking?
private static readonly object cacheLock = new object();
public static T GetFromCache<T>(string cacheKey, Func<T> GetData) where T : class {
// Returns null if the string does not exist, prevents a race condition
// where the cache invalidates between the contains check and the retrieval.
T cachedData = MemoryCache.Default.Get(cacheKey) as T;
if (cachedData != null) {
return cachedData;
}
lock (cacheLock) {
// Check to see if anyone wrote to the cache while we where
// waiting our turn to write the new value.
cachedData = MemoryCache.Default.Get(cacheKey) as T;
if (cachedData != null) {
return cachedData;
}
// The value still did not exist so we now write it in to the cache.
cachedData = GetData();
MemoryCache.Default.Set(cacheKey, cachedData, new CacheItemPolicy(...));
return cachedData;
}
}

You may want to consider using ReaderWriterLockSlim, which you can obtain write lock only when needed.
Using cacheLock.EnterReadLock(); and cacheLock.EnterWriteLock(); should greatly improve the performance.
That link I gave even have an example of a cache, exactly what you need, I copy here:
public class SynchronizedCache
{
private ReaderWriterLockSlim cacheLock = new ReaderWriterLockSlim();
private Dictionary<int, string> innerCache = new Dictionary<int, string>();
public int Count
{ get { return innerCache.Count; } }
public string Read(int key)
{
cacheLock.EnterReadLock();
try
{
return innerCache[key];
}
finally
{
cacheLock.ExitReadLock();
}
}
public void Add(int key, string value)
{
cacheLock.EnterWriteLock();
try
{
innerCache.Add(key, value);
}
finally
{
cacheLock.ExitWriteLock();
}
}
public bool AddWithTimeout(int key, string value, int timeout)
{
if (cacheLock.TryEnterWriteLock(timeout))
{
try
{
innerCache.Add(key, value);
}
finally
{
cacheLock.ExitWriteLock();
}
return true;
}
else
{
return false;
}
}
public AddOrUpdateStatus AddOrUpdate(int key, string value)
{
cacheLock.EnterUpgradeableReadLock();
try
{
string result = null;
if (innerCache.TryGetValue(key, out result))
{
if (result == value)
{
return AddOrUpdateStatus.Unchanged;
}
else
{
cacheLock.EnterWriteLock();
try
{
innerCache[key] = value;
}
finally
{
cacheLock.ExitWriteLock();
}
return AddOrUpdateStatus.Updated;
}
}
else
{
cacheLock.EnterWriteLock();
try
{
innerCache.Add(key, value);
}
finally
{
cacheLock.ExitWriteLock();
}
return AddOrUpdateStatus.Added;
}
}
finally
{
cacheLock.ExitUpgradeableReadLock();
}
}
public void Delete(int key)
{
cacheLock.EnterWriteLock();
try
{
innerCache.Remove(key);
}
finally
{
cacheLock.ExitWriteLock();
}
}
public enum AddOrUpdateStatus
{
Added,
Updated,
Unchanged
};
~SynchronizedCache()
{
if (cacheLock != null) cacheLock.Dispose();
}
}

I don't know how MemoryCache.Default is implemented, or whether or not you have control over it.
But in general, prefer using ConcurrentDictionary over Dictionary with lock in a multi threaded environment.
GetFromCache would just become
ConcurrentDictionary<string, T> cache = new ConcurrentDictionary<string, T>();
...
cache.GetOrAdd("someKey", (key) =>
{
var data = PullDataFromDatabase(key);
return data;
});
There are two more things to take care about.
Expiry
Instead of saving T as the value of the dictionary, you can define a type
struct CacheItem<T>
{
public T Item { get; set; }
public DateTime Expiry { get; set; }
}
And store the cache as a CacheItem with a defined expiry.
cache.GetOrAdd("someKey", (key) =>
{
var data = PullDataFromDatabase(key);
return new CacheItem<T>() { Item = data, Expiry = DateTime.UtcNow.Add(TimeSpan.FromHours(1)) };
});
Now you can implement expiration in an asynchronous thread.
Timer expirationTimer = new Timer(ExpireCache, null, 60000, 60000);
...
void ExpireCache(object state)
{
var needToExpire = cache.Where(c => DateTime.UtcNow >= c.Value.Expiry).Select(c => c.Key);
foreach (var key in needToExpire)
{
cache.TryRemove(key, out CacheItem<T> _);
}
}
Once a minute, you search for all cache entries that need to be expired, and remove them.
"Locking"
Using ConcurrentDictionary guarantees that simultaneous read/writes won't corrupt the dictionary or throw an exception.
But, you can still end up with a situation where two simultaneous reads cause you to fetch the data from the database twice.
One neat trick to solve this is to wrap the value of the dictionary with Lazy
ConcurrentDictionary<string, Lazy<CacheItem<T>>> cache = new ConcurrentDictionary<string, Lazy<CacheItem<T>>>();
...
var data = cache.GetOrData("someKey", key => new Lazy<CacheItem<T>>(() =>
{
var data = PullDataFromDatabase(key);
return new CacheItem<T>() { Item = data, Expiry = DateTime.UtcNow.Add(TimeSpan.FromHours(1)) };
})).Value;
Explanation
with GetOrAdd you might end up invoking the "get from database if not in cache" delegate multiple times in the case of simultaneous requests.
However, GetOrAdd will end up using only one of the values that the delegate returned, and by returning a Lazy, you guaranty that only one Lazy will get invoked.

Do not expire cached item in IMemoryCache implementation

Since IMemoryCache does not give too much info about the cached items I was thinking to implement something custom in order to keep some data about items in the cache like the key, AbsoluteExpiration properties etc.
Here is my implementation of IMemoryCache:
public class MemoryCacheService : IMemoryCache
{
private readonly MemoryCache _memoryCache;
private readonly List<CacheItemRelevantData> _allKeys;
private readonly string AllKeys = "___All__Keys___";
public MemoryCacheService()
{
_memoryCache = new MemoryCache(new MemoryCacheOptions());
_allKeys = new List<CacheItemRelevantData>();
_memoryCache.Set(AllKeys, _allKeys, new MemoryCacheEntryOptions
{
AbsoluteExpiration = DateTimeOffset.MaxValue
});
}
public void Dispose()
{
_memoryCache.Dispose();
}
public bool TryGetValue(object key, out object value)
{
return _memoryCache.TryGetValue(key, out value);
}
public ICacheEntry CreateEntry(object key)
{
var entry = _memoryCache.CreateEntry(key);
entry.RegisterPostEvictionCallback((o, v, reason, state) =>
{
if (reason.In(EvictionReason.Capacity, EvictionReason.Expired, EvictionReason.TokenExpired))
{
var item = _allKeys.FirstOrDefault(x => x.Key.ToString() == o.ToString());
if (item != null)
{
_allKeys.Remove(item);
}
}
});
if (!_allKeys.Select(x => x.Key).Contains(key))
{
_allKeys.Add(new CacheItemRelevantData
{
Key = entry.Key,
AbsoluteExpiration = entry.AbsoluteExpiration,
Priority = entry.Priority,
AbsoluteExpirationRelativeToNow = entry.AbsoluteExpirationRelativeToNow,
Size = entry.Size
});
}
return entry;
}
public void Remove(object key)
{
var entry = _allKeys.FirstOrDefault(x => x.Key.ToString() == key.ToString());
if (entry != null)
{
_allKeys.Remove(entry);
}
_memoryCache.Remove(key);
}
}
But since _allKeys is created to store the relevant data about cached items I dont want it to expire.
Is there any way to set expire time to none or something similar and the _allKeys list will remain in cache forever ?

For my case I could easily solve the problem because the IMemoryService was configured as scoped service and that means _allKeys variable is persisting in memory as far IMemoryService instance(until the iis is restarted or something). For non-scoped service I did not find a proper solution but I think IMemoryCache service should always be a scoped service(there is no real case to have it configured differently -maybe!!)

Call code once when controller is first accessed [duplicate]

I have read lots of information about page caching and partial page caching in a MVC application. However, I would like to know how you would cache data.
In my scenario I will be using LINQ to Entities (entity framework). On the first call to GetNames (or whatever the method is) I want to grab the data from the database. I want to save the results in cache and on the second call to use the cached version if it exists.
Can anyone show an example of how this would work, where this should be implemented (model?) and if it would work.
I have seen this done in traditional ASP.NET apps , typically for very static data.

Here's a nice and simple cache helper class/service I use:
using System.Runtime.Caching;
public class InMemoryCache: ICacheService
{
public T GetOrSet<T>(string cacheKey, Func<T> getItemCallback) where T : class
{
T item = MemoryCache.Default.Get(cacheKey) as T;
if (item == null)
{
item = getItemCallback();
MemoryCache.Default.Add(cacheKey, item, DateTime.Now.AddMinutes(10));
}
return item;
}
}
interface ICacheService
{
T GetOrSet<T>(string cacheKey, Func<T> getItemCallback) where T : class;
}
Usage:
cacheProvider.GetOrSet("cache key", (delegate method if cache is empty));
Cache provider will check if there's anything by the name of "cache id" in the cache, and if there's not, it will call a delegate method to fetch data and store it in cache.
Example:
var products=cacheService.GetOrSet("catalog.products", ()=>productRepository.GetAll())

Reference the System.Web dll in your model and use System.Web.Caching.Cache
public string[] GetNames()
{
string[] names = Cache["names"] as string[];
if(names == null) //not in cache
{
names = DB.GetNames();
Cache["names"] = names;
}
return names;
}
A bit simplified but I guess that would work. This is not MVC specific and I have always used this method for caching data.

I'm referring to TT's post and suggest the following approach:
Reference the System.Web dll in your model and use System.Web.Caching.Cache
public string[] GetNames()
{
var noms = Cache["names"];
if(noms == null)
{
noms = DB.GetNames();
Cache["names"] = noms;
}
return ((string[])noms);
}
You should not return a value re-read from the cache, since you'll never know if at that specific moment it is still in the cache. Even if you inserted it in the statement before, it might already be gone or has never been added to the cache - you just don't know.
So you add the data read from the database and return it directly, not re-reading from the cache.

For .NET 4.5+ framework
add reference: System.Runtime.Caching
add using statement:
using System.Runtime.Caching;
public string[] GetNames()
{
var noms = System.Runtime.Caching.MemoryCache.Default["names"];
if(noms == null)
{
noms = DB.GetNames();
System.Runtime.Caching.MemoryCache.Default["names"] = noms;
}
return ((string[])noms);
}
In the .NET Framework 3.5 and earlier versions, ASP.NET provided an in-memory cache implementation in the System.Web.Caching namespace. In previous versions of the .NET Framework, caching was available only in the System.Web namespace and therefore required a dependency on ASP.NET classes. In the .NET Framework 4, the System.Runtime.Caching namespace contains APIs that are designed for both Web and non-Web applications.
More info:
https://msdn.microsoft.com/en-us/library/dd997357(v=vs.110).aspx
https://learn.microsoft.com/en-us/dotnet/framework/performance/caching-in-net-framework-applications

Steve Smith did two great blog posts which demonstrate how to use his CachedRepository pattern in ASP.NET MVC. It uses the repository pattern effectively and allows you to get caching without having to change your existing code.
http://ardalis.com/Introducing-the-CachedRepository-Pattern
http://ardalis.com/building-a-cachedrepository-via-strategy-pattern
In these two posts he shows you how to set up this pattern and also explains why it is useful. By using this pattern you get caching without your existing code seeing any of the caching logic. Essentially you use the cached repository as if it were any other repository.

I have used it in this way and it works for me.
https://msdn.microsoft.com/en-us/library/system.web.caching.cache.add(v=vs.110).aspx
parameters info for system.web.caching.cache.add.
public string GetInfo()
{
string name = string.Empty;
if(System.Web.HttpContext.Current.Cache["KeyName"] == null)
{
name = GetNameMethod();
System.Web.HttpContext.Current.Cache.Add("KeyName", name, null, DateTime.Noew.AddMinutes(5), Cache.NoSlidingExpiration, CacheitemPriority.AboveNormal, null);
}
else
{
name = System.Web.HttpContext.Current.Cache["KeyName"] as string;
}
return name;
}

AppFabric Caching is distributed and an in-memory caching technic that stores data in key-value pairs using physical memory across multiple servers. AppFabric provides performance and scalability improvements for .NET Framework applications. Concepts and Architecture

Extending #Hrvoje Hudo's answer...
Code:
using System;
using System.Runtime.Caching;
public class InMemoryCache : ICacheService
{
public TValue Get<TValue>(string cacheKey, int durationInMinutes, Func<TValue> getItemCallback) where TValue : class
{
TValue item = MemoryCache.Default.Get(cacheKey) as TValue;
if (item == null)
{
item = getItemCallback();
MemoryCache.Default.Add(cacheKey, item, DateTime.Now.AddMinutes(durationInMinutes));
}
return item;
}
public TValue Get<TValue, TId>(string cacheKeyFormat, TId id, int durationInMinutes, Func<TId, TValue> getItemCallback) where TValue : class
{
string cacheKey = string.Format(cacheKeyFormat, id);
TValue item = MemoryCache.Default.Get(cacheKey) as TValue;
if (item == null)
{
item = getItemCallback(id);
MemoryCache.Default.Add(cacheKey, item, DateTime.Now.AddMinutes(durationInMinutes));
}
return item;
}
}
interface ICacheService
{
TValue Get<TValue>(string cacheKey, Func<TValue> getItemCallback) where TValue : class;
TValue Get<TValue, TId>(string cacheKeyFormat, TId id, Func<TId, TValue> getItemCallback) where TValue : class;
}
Examples
Single item caching (when each item is cached based on its ID because caching the entire catalog for the item type would be too intensive).
Product product = cache.Get("product_{0}", productId, 10, productData.getProductById);
Caching all of something
IEnumerable<Categories> categories = cache.Get("categories", 20, categoryData.getCategories);
Why TId
The second helper is especially nice because most data keys are not composite. Additional methods could be added if you use composite keys often. In this way you avoid doing all sorts of string concatenation or string.Formats to get the key to pass to the cache helper. It also makes passing the data access method easier because you don't have to pass the ID into the wrapper method... the whole thing becomes very terse and consistant for the majority of use cases.

Here's an improvement to Hrvoje Hudo's answer. This implementation has a couple of key improvements:
Cache keys are created automatically based on the function to update data and the object passed in that specifies dependencies
Pass in time span for any cache duration
Uses a lock for thread safety
Note that this has a dependency on Newtonsoft.Json to serialize the dependsOn object, but that can be easily swapped out for any other serialization method.
ICache.cs
public interface ICache
{
T GetOrSet<T>(Func<T> getItemCallback, object dependsOn, TimeSpan duration) where T : class;
}
InMemoryCache.cs
using System;
using System.Reflection;
using System.Runtime.Caching;
using Newtonsoft.Json;
public class InMemoryCache : ICache
{
private static readonly object CacheLockObject = new object();
public T GetOrSet<T>(Func<T> getItemCallback, object dependsOn, TimeSpan duration) where T : class
{
string cacheKey = GetCacheKey(getItemCallback, dependsOn);
T item = MemoryCache.Default.Get(cacheKey) as T;
if (item == null)
{
lock (CacheLockObject)
{
item = getItemCallback();
MemoryCache.Default.Add(cacheKey, item, DateTime.Now.Add(duration));
}
}
return item;
}
private string GetCacheKey<T>(Func<T> itemCallback, object dependsOn) where T: class
{
var serializedDependants = JsonConvert.SerializeObject(dependsOn);
var methodType = itemCallback.GetType();
return methodType.FullName + serializedDependants;
}
}
Usage:
var order = _cache.GetOrSet(
() => _session.Set<Order>().SingleOrDefault(o => o.Id == orderId)
, new { id = orderId }
, new TimeSpan(0, 10, 0)
);

public sealed class CacheManager
{
private static volatile CacheManager instance;
private static object syncRoot = new Object();
private ObjectCache cache = null;
private CacheItemPolicy defaultCacheItemPolicy = null;
private CacheEntryRemovedCallback callback = null;
private bool allowCache = true;
private CacheManager()
{
cache = MemoryCache.Default;
callback = new CacheEntryRemovedCallback(this.CachedItemRemovedCallback);
defaultCacheItemPolicy = new CacheItemPolicy();
defaultCacheItemPolicy.AbsoluteExpiration = DateTime.Now.AddHours(1.0);
defaultCacheItemPolicy.RemovedCallback = callback;
allowCache = StringUtils.Str2Bool(ConfigurationManager.AppSettings["AllowCache"]); ;
}
public static CacheManager Instance
{
get
{
if (instance == null)
{
lock (syncRoot)
{
if (instance == null)
{
instance = new CacheManager();
}
}
}
return instance;
}
}
public IEnumerable GetCache(String Key)
{
if (Key == null || !allowCache)
{
return null;
}
try
{
String Key_ = Key;
if (cache.Contains(Key_))
{
return (IEnumerable)cache.Get(Key_);
}
else
{
return null;
}
}
catch (Exception)
{
return null;
}
}
public void ClearCache(string key)
{
AddCache(key, null);
}
public bool AddCache(String Key, IEnumerable data, CacheItemPolicy cacheItemPolicy = null)
{
if (!allowCache) return true;
try
{
if (Key == null)
{
return false;
}
if (cacheItemPolicy == null)
{
cacheItemPolicy = defaultCacheItemPolicy;
}
String Key_ = Key;
lock (Key_)
{
return cache.Add(Key_, data, cacheItemPolicy);
}
}
catch (Exception)
{
return false;
}
}
private void CachedItemRemovedCallback(CacheEntryRemovedArguments arguments)
{
String strLog = String.Concat("Reason: ", arguments.RemovedReason.ToString(), " | Key-Name: ", arguments.CacheItem.Key, " | Value-Object: ", arguments.CacheItem.Value.ToString());
LogManager.Instance.Info(strLog);
}
}

I use two classes. First one the cache core object:
public class Cacher<TValue>
where TValue : class
{
#region Properties
private Func<TValue> _init;
public string Key { get; private set; }
public TValue Value
{
get
{
var item = HttpRuntime.Cache.Get(Key) as TValue;
if (item == null)
{
item = _init();
HttpContext.Current.Cache.Insert(Key, item);
}
return item;
}
}
#endregion
#region Constructor
public Cacher(string key, Func<TValue> init)
{
Key = key;
_init = init;
}
#endregion
#region Methods
public void Refresh()
{
HttpRuntime.Cache.Remove(Key);
}
#endregion
}
Second one is list of cache objects:
public static class Caches
{
static Caches()
{
Languages = new Cacher<IEnumerable<Language>>("Languages", () =>
{
using (var context = new WordsContext())
{
return context.Languages.ToList();
}
});
}
public static Cacher<IEnumerable<Language>> Languages { get; private set; }
}

I will say implementing Singleton on this persisting data issue can be a solution for this matter in case you find previous solutions much complicated
public class GPDataDictionary
{
private Dictionary<string, object> configDictionary = new Dictionary<string, object>();
/// <summary>
/// Configuration values dictionary
/// </summary>
public Dictionary<string, object> ConfigDictionary
{
get { return configDictionary; }
}
private static GPDataDictionary instance;
public static GPDataDictionary Instance
{
get
{
if (instance == null)
{
instance = new GPDataDictionary();
}
return instance;
}
}
// private constructor
private GPDataDictionary() { }
} // singleton

HttpContext.Current.Cache.Insert("subjectlist", subjectlist);

You can also try and use the caching built into ASP MVC:
Add the following attribute to the controller method you'd like to cache:
[OutputCache(Duration=10)]
In this case the ActionResult of this will be cached for 10 seconds.
More on this here

how use caching in asp.net mvc3?

I have problem with cache in my asp.net mvc3 application.
My code
using System.Web.Caching;
...
class RegularCacheProvider : ICacheProvider
{
Cache cache ;
public object Get(string name)
{
return cache[name];
}
public void Set(string name, object value)
{
cache.Insert(name, value);
}
public void Unset(string name)
{
cache.Remove(name);
}
}
And I use singleton for give value for it :
School schoolSettings = (School)CacheProviderFactory.Cache.Get("SchoolSettings");
if (schoolSettings == null)
{
CacheProviderFactory.Cache.Set("SchoolSettings", someObject);
}
So in first use it does not work and give me an error cache[name] is null.
What I'm doing wrong?
Any help would be appreciated.

At no point have you given cache a value... and note that the regular web cache probably isn't your best bet if you want it separate; perhaps
MemoryCache cache = new MemoryCache();

What about using the HttpRuntime.Cache, this example would cache for an hour?
HttpRuntime.Cache.Add("SchoolSettings", someObject, null, DateTime.Now.AddHours(1),
System.Web.Caching.Cache.NoSlidingExpiration,
System.Web.Caching.CacheItemPriority.Normal, null);

Try the following code. it works fine for my project
using System.Runtime.Caching;
public class RegularCacheProvider : ICacheProvider
{
private ObjectCache Cache { get { return MemoryCache.Default; } }
object ICacheProvider.Get(string key)
{
return Cache[key];
}
void ICacheProvider.Set(string key, object data, int cacheTime = 30)
{
var policy = new CacheItemPolicy {AbsoluteExpiration = DateTime.Now + TimeSpan.FromMinutes(cacheTime)};
Cache.Add(new CacheItem(key, data), policy);
}
void ICacheProvider.Unset(string key)
{
Cache.Remove(key);
}
}

Change the code where you check for the value as follow:
School schoolSettings = CacheProviderFactory.Cache.Get("SchoolSettings") as (School);
Notice that I am using "as" rather than casting the object. Cast will blow up if the value is null while "as" will just give you a null value which is what you expect.

MVC 2 - Caching Strings in Memory

I would like to cache strings in memory from the database so that I do not have to access the database every time. I tried using System.Runtime.Caching, but it does not seem to work.
On the local site, all the data is cached but the user has to be authenticated on a secondary site. Once the user is authenticated, they are brought back to the local site but all the data that was cached is gone.
Is there a way to fix the above issue? Below is part of my code:
using System.Runtime.Caching;
ObjectCache cache = MemoryCache.Default;
public bool CacheIsSet(string key)
{
return cache.Contains(key);
}
public object CacheGet(string key)
{
return cache.Get(key);
}
public void CacheSet(string key, object value)
{
CacheItemPolicy policy = new CacheItemPolicy();
cache.Set(key, value, policy);
}
Thanks very much.

You should be referencing the HttpRuntime.Cache object. I created a wrapper around this, similar to what you have referenced in your question. Feel free to use it:
using System.Web.Caching;
public class CachingService
{
protected Cache Cache
{
get;
set;
}
public int CacheDurationMinutes
{
get;
set;
}
public CachingService()
{
Cache = HttpRuntime.Cache;
CacheDurationMinutes = 60;
}
public virtual object Get(string keyname)
{
return Cache[keyname];
}
public virtual T Get<T>(string keyname)
{
T item = (T)Cache[keyname];
return item;
}
public virtual void Insert(string keyname, object item)
{
Cache.Insert(keyname, item, null, DateTime.UtcNow.AddMinutes(CacheDurationMinutes), Cache.NoSlidingExpiration);
}
public virtual void Insert(string keyname, object item, CacheDependency dependency)
{
Cache.Insert(keyname, item, dependency);
}
public virtual void Remove(string keyname)
{
Cache.Remove(keyname);
}
}
Here is a sample use case. The function LoadPosts is supposed to load blog posts to display on the site. The function will first see if the posts are cached, if not it will load the posts from the database, and then cache them:
public IEnumerable<BlogPost> LoadPosts()
{
var cacheService = new CachingService();
var blogPosts = cacheService.Get<IEnumerable<BlogPost>>("BlogPosts");
if (blogPosts == null)
{
blogPosts = postManager.LoadPostsFromDatabase();
cacheService.Insert("BlogPosts", blogPosts);
}
return blogPosts;
}
The first time this function is run, the cache will return null, because we didn't add anything to the BlogPosts key yet. The second time the function is called the posts will be in the cache and the code in the if block will not run, saving us a trip to the database.