跨 HttpHandler 请求实现 Singleton
我正在尝试创建一个单例服务，用于处理对 HttpHandler 的传入请求。目前，该服务正在根据每个请求进行实例化。我调用保存服务实例的静态类，作为单例实现，如下所示：
public static class ServerApplication {
static Service instance = null;
static readonly object padlock = new object();
/// <summary>
/// Service singleton.
/// </summary>
public static Service Service {
get {
lock (padlock) {
if (instance == null) {
instance = new Service();
}
return instance;
}
}
}
并使用 HttpHandler 中的调用访问它，如下所示：
ServerApplication.Service.Process(request);
我已在 instance = new Service( ); 行并且有多个请求 每个请求都会触发断点。
我的目标是一种跨请求存在的服务，因为它加载和缓存来自文件和数据库的大量数据，这些数据可被大多数请求重用。
任何人都可以看到出了什么问题吗？
I am attempting to create a singleton service that is used to process incoming requests to an HttpHandler. At the moment the service is being instantiated on every request. I make a call to the static class that holds an instance of the service, implemented as a singleton as below:
public static class ServerApplication {
static Service instance = null;
static readonly object padlock = new object();
/// <summary>
/// Service singleton.
/// </summary>
public static Service Service {
get {
lock (padlock) {
if (instance == null) {
instance = new Service();
}
return instance;
}
}
}
And access it using a call as below in the HttpHandler:
ServerApplication.Service.Process(request);
I have set a breakpoint on the instance = new Service(); line and with multiple requests the
breakpoint is triggered per request.
My aim is a service that exists across requests as it loads and caches lots of data from files and databases that is reused with most requests.
Can anyone see what is going wrong?
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评论（3）
有几点：
这应该涵盖并发方面的内容。也有可能（尽管不太可能）您的 AppDomain 在请求之间被卸载（即，您在 Web 目录中写入了一个文件，导致 ASP.NET 认为您的应用程序已过时），这将导致静态数据被重置。
A couple of things:
That should cover you on the concurrency fronts. It's also possible (though less likely) that your AppDomain is being unloaded between requests (ie, you wrote a file inside the web directory causing ASP.NET to think your app is stale), which would cause the statics to be reset.
HTTP 设计用于建立多个并发连接，我不知道您是否想要打破它，除非您在页面加载时建立很少的连接。也就是说，也许您可以将 HttpHandler 保留在 Session 中？
HTTP is designed to make several concurrent connections, I don't know that you'd want to break this, unless you make very few connections on page loads. That said, perhaps you could keep the HttpHandler in the Session?
一般来说，如果你想要一个单例 - 不知道是否有必要，我通常这样实现它： http://www.vikingworks.dk/page/Creating-a-Singleton-Pattern-iC.aspx
Generally speaking, if you want a singleton - cannot see if its necessary i usually implement it this way: http://www.vikingworks.dk/page/Creating-a-Singleton-Pattern-i-C.aspx