什么是最好的方式来锁缓存在asp.net?
https://stackoverflow.com/questions/39112
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我知道在某些情况下，例如很长的运行的流程，重要的是要锁定ASP.NET 高速缓存在，以避免随后请求通过另一个用户对该资源从执行长期的过程，而不是撞击高速缓存。
什么是最好的方式在c#来实现高速缓存在锁定ASP.NET?
解决方案
这里的基本模式：
- 检查高速缓存的价值，如果返回其提供
- 如果价值是不是在缓，然后执行一个锁
- 里面锁，检查缓再次，你可能已经封锁
- 执行的价值观和缓存
- 释放锁
在代码，它看起来像这样：
private static object ThisLock = new object();
public string GetFoo()
{
// try to pull from cache here
lock (ThisLock)
{
// cache was empty before we got the lock, check again inside the lock
// cache is still empty, so retreive the value here
// store the value in the cache here
}
// return the cached value here
}
其他提示
为了完整性的一个完整的例子看起来像这样的东西。
private static object ThisLock = new object();
...
object dataObject = Cache["globalData"];
if( dataObject == null )
{
lock( ThisLock )
{
dataObject = Cache["globalData"];
if( dataObject == null )
{
//Get Data from db
dataObject = GlobalObj.GetData();
Cache["globalData"] = dataObject;
}
}
}
return dataObject;
只是为了回波什么帕维尔说的，我相信这是最线安全的方式编写它
private T GetOrAddToCache<T>(string cacheKey, GenericObjectParamsDelegate<T> creator, params object[] creatorArgs) where T : class, new()
{
T returnValue = HttpContext.Current.Cache[cacheKey] as T;
if (returnValue == null)
{
lock (this)
{
returnValue = HttpContext.Current.Cache[cacheKey] as T;
if (returnValue == null)
{
returnValue = creator(creatorArgs);
if (returnValue == null)
{
throw new Exception("Attempt to cache a null reference");
}
HttpContext.Current.Cache.Add(
cacheKey,
returnValue,
null,
System.Web.Caching.Cache.NoAbsoluteExpiration,
System.Web.Caching.Cache.NoSlidingExpiration,
CacheItemPriority.Normal,
null);
}
}
}
return returnValue;
}
没有必要锁整个缓存的实例，而我们只需要锁的具体的关键，你是插入。I.e。没有必要阻止访问在女卫生间同时使用男卫生间:)
执行以下允许对锁定的具体缓键用一个并发的字典。这样你就可以运行GetOrAdd()用于两个不同的钥匙在同一时间-但不是同样的关键在同一时间。
using System;
using System.Collections.Concurrent;
using System.Web.Caching;
public static class CacheExtensions
{
private static ConcurrentDictionary<string, object> keyLocks = new ConcurrentDictionary<string, object>();
/// <summary>
/// Get or Add the item to the cache using the given key. Lazily executes the value factory only if/when needed
/// </summary>
public static T GetOrAdd<T>(this Cache cache, string key, int durationInSeconds, Func<T> factory)
where T : class
{
// Try and get value from the cache
var value = cache.Get(key);
if (value == null)
{
// If not yet cached, lock the key value and add to cache
lock (keyLocks.GetOrAdd(key, new object()))
{
// Try and get from cache again in case it has been added in the meantime
value = cache.Get(key);
if (value == null && (value = factory()) != null)
{
// TODO: Some of these parameters could be added to method signature later if required
cache.Insert(
key: key,
value: value,
dependencies: null,
absoluteExpiration: DateTime.Now.AddSeconds(durationInSeconds),
slidingExpiration: Cache.NoSlidingExpiration,
priority: CacheItemPriority.Default,
onRemoveCallback: null);
}
// Remove temporary key lock
keyLocks.TryRemove(key, out object locker);
}
}
return value as T;
}
}
克雷格鞋匠已经做出了出色的表演上asp.net 缓存：http://polymorphicpodcast.com/shows/webperformance/
我已经想出了以下扩展的方法：
private static readonly object _lock = new object();
public static TResult GetOrAdd<TResult>(this Cache cache, string key, Func<TResult> action, int duration = 300) {
TResult result;
var data = cache[key]; // Can't cast using as operator as TResult may be an int or bool
if (data == null) {
lock (_lock) {
data = cache[key];
if (data == null) {
result = action();
if (result == null)
return result;
if (duration > 0)
cache.Insert(key, result, null, DateTime.UtcNow.AddSeconds(duration), TimeSpan.Zero);
} else
result = (TResult)data;
}
} else
result = (TResult)data;
return result;
}
我已经使用两@约翰*欧文和@user378380的答案。我的解决方案可以存储int和bool值高速缓存内。
请纠正我，如果有任何错误或是否可以写好一点。
我看到一个模式最近所谓的正确状态袋访问模式，这似乎触及这一点。
我修改了一点应线的安全。
http://weblogs.asp.net/craigshoemaker/archive/2008/08/28/asp-net-caching-and-performance.aspx
private static object _listLock = new object();
public List List() {
string cacheKey = "customers";
List myList = Cache[cacheKey] as List;
if(myList == null) {
lock (_listLock) {
myList = Cache[cacheKey] as List;
if (myList == null) {
myList = DAL.ListCustomers();
Cache.Insert(cacheKey, mList, null, SiteConfig.CacheDuration, TimeSpan.Zero);
}
}
}
return myList;
}
这篇文章从CodeGuru解释了各种缓锁定方案以及一些最佳做法ASP.NET 缓锁定：
我修改@user378380的代码的更多的灵活性。而不是返回此委托现在返回的对象接受不同类型秩序。还增加了一些参数的灵活性。所有的想法属于 @user378380.
private static readonly object _lock = new object();
//If getOnly is true, only get existing cache value, not updating it. If cache value is null then set it first as running action method. So could return old value or action result value.
//If getOnly is false, update the old value with action result. If cache value is null then set it first as running action method. So always return action result value.
//With oldValueReturned boolean we can cast returning object(if it is not null) appropriate type on main code.
public static object GetOrAdd<TResult>(this Cache cache, string key, Func<TResult> action,
DateTime absoluteExpireTime, TimeSpan slidingExpireTime, bool getOnly, out bool oldValueReturned)
{
object result;
var data = cache[key];
if (data == null)
{
lock (_lock)
{
data = cache[key];
if (data == null)
{
oldValueReturned = false;
result = action();
if (result == null)
{
return result;
}
cache.Insert(key, result, null, absoluteExpireTime, slidingExpireTime);
}
else
{
if (getOnly)
{
oldValueReturned = true;
result = data;
}
else
{
oldValueReturned = false;
result = action();
if (result == null)
{
return result;
}
cache.Insert(key, result, null, absoluteExpireTime, slidingExpireTime);
}
}
}
}
else
{
if(getOnly)
{
oldValueReturned = true;
result = data;
}
else
{
oldValueReturned = false;
result = action();
if (result == null)
{
return result;
}
cache.Insert(key, result, null, absoluteExpireTime, slidingExpireTime);
}
}
return result;
}
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