我们知道项目中创建的Controller,如ProductController都继承自ApiController抽象类,其又实现了接口IDisposable,所以,框架中自动调用Dispose方法来释放其资源。在代表请求的HttpRequestMessage属性字典中,有个Key,“Ms_DisposableRequestResources” ,其值是类型List<IDisposable>,用来存放待释放的资源,回顾下ApiController抽象类的方法ExecuteAsync里的代码片段。 

ASP.NET Web API 框架研究 Controller实例的销毁-LMLPHP

  Request.RegisterForDispose(this)是主要代码,我们看下HttpRequestMessage的相关扩展方法,RegisterForDispose注册销毁资源,DisposeRequestResources释放所有资源。

public static class HttpRequestMessageExtensions
{
//注册一个待销毁的资源列表到请求的属性字典中
public static void RegisterForDispose(this HttpRequestMessage request, IDisposable resource)
{
if (request == null)
{
throw Error.ArgumentNull("request");
} if (resource == null)
{
return;
} List<IDisposable> trackedResources = GetRegisteredResourcesForDispose(request); trackedResources.Add(resource);
} //一次性注册多个待销毁的资源列表到请求的属性字典中
public static void RegisterForDispose(this HttpRequestMessage request, IEnumerable<IDisposable> resources)
{
if (request == null)
{
throw Error.ArgumentNull("request");
} if (resources == null)
{
throw Error.ArgumentNull("resources");
} List<IDisposable> trackedResources = GetRegisteredResourcesForDispose(request); foreach (IDisposable resource in resources)
{
if (resource != null)
{
trackedResources.Add(resource);
}
}
} //释放资源列表(RegisterForDispose方法注册)里的所有资源
public static void DisposeRequestResources(this HttpRequestMessage request)
{
if (request == null)
{
throw Error.ArgumentNull("request");
} List<IDisposable> resourcesToDispose;
if (request.Properties.TryGetValue(HttpPropertyKeys.DisposableRequestResourcesKey, out resourcesToDispose))
{
foreach (IDisposable resource in resourcesToDispose)
{
try
{
resource.Dispose();
}
catch
{
// ignore exceptions
}
}
//清空列表
resourcesToDispose.Clear();
}
} //从当前请求中获取所有待销毁的资源的列表
public static IEnumerable<IDisposable> GetResourcesForDisposal(this HttpRequestMessage request)
{
if (request == null)
{
throw Error.ArgumentNull("request");
} return GetRegisteredResourcesForDispose(request);
} //从当前请求中获取所有待销毁的资源的列表
private static List<IDisposable> GetRegisteredResourcesForDispose(HttpRequestMessage request)
{
List<IDisposable> registeredResourcesForDispose;
//从属性字典中,获取指定Key的值
if (!request.Properties.TryGetValue(HttpPropertyKeys.DisposableRequestResourcesKey, out registeredResourcesForDispose))
{
registeredResourcesForDispose = new List<IDisposable>();
request.Properties[HttpPropertyKeys.DisposableRequestResourcesKey] = registeredResourcesForDispose;
}
return registeredResourcesForDispose;
}
}

一、WebHost 模式下的资源销毁

  ASP.NET Web API用于“处理请求、回复响应”的 HttpMessageHandler管道是由 HttpControllerHandler创建的,后者根据当前HTTP上下文创建一个表示当前请求的HttpRequestMessage对象并传入这个管道进行处理 。在整个管道完成对请求的处理并最终对请求予以响应之后 ,HttpControllerHandler会负责完成资源释放有关的工作

工作。回顾下HttpControllerHandler,方法的代码:

public  class HttpControllerHandler:HttpTaskAsyncHandler
{
//省略其他成员 public HttpControllerHandler(RouteData routeData)
: this(routeData, GlobalConfiguration.DefaultServer)
{
} public override Task ProcessRequestAsync(HttpContext context)
{
return ProcessRequestAsyncCore(new HttpContextWrapper(context));
} internal async Task ProcessRequestAsyncCore(HttpContextBase contextBase)
{
HttpRequestMessage request = contextBase.GetHttpRequestMessage() ?? ConvertRequest(contextBase); // Add route data
request.SetRouteData(_routeData);
CancellationToken cancellationToken = contextBase.Response.GetClientDisconnectedTokenWhenFixed();
HttpResponseMessage response = null; try
{
//创建消息处理管道,并执行
response = await _server.SendAsync(request, cancellationToken);
//异步执行完成
await CopyResponseAsync(contextBase, request, response, _exceptionLogger.Value, _exceptionHandler.Value,
cancellationToken);
}
catch (OperationCanceledException)
{ contextBase.Request.Abort();
}
finally
{
//1.调用方法DisposeRequestResources释放属性字典中的待释放资源
         request.DisposeRequestResources();
         //2.释放请求消息
        request.Dispose();
         //3.释放响应消息
if (response != null)
{
response.Dispose();
}
}
}
}

  从代码可知道,创建管道并执行完成后,在finally代码块里释放了三种资源,

  • 调用方法DisposeRequestResources释放属性字典中的待释放资源
  • 请求消息
  • 响应消息

二、Self Host模式下的资源销毁

  Self Host模式下的请求的监听、接收和响应是通过HttpBinding创建的信道栈来完成的,该信道栈处理的消息类型为HttpMessage,具体代表请求消息和响应消息的HttpMesmge分别是对HttpRequestMessage和Message对象的封装。WCF中表示消息的Message本身就是一个需要最终被释放的对象,在针对它的处理结束之后会调用其Close或 者 Dispose方法对它进行资源释放的工作。再看下代码段

internal sealed class HttpMessage : Message
{
//省略其他成员
protected override void OnClose()
{
base.Close();
if (_request != null)
{
//1.调用DisposeRequestResources,释放属性字典中注册的资源
_request.DisposeRequestResources();
//2.释放请求消息
_request.Dispose();
_request = null;
}
//3.释放响应消息
if (_response != null)
{
_response.Dispose();
_response = null;
}
}
}
 internal sealed class Message : IDisposable
{
protected virtual void OnClose()
{
} public void Close()
{
if (this.state != MessageState.Closed)
{
this.state = MessageState.Closed;
//调用OnClose()
this.OnClose();
if (!System.ServiceModel.DiagnosticUtility.ShouldTraceVerbose)
return;
TraceUtility.TraceEvent(TraceEventType.Verbose, , System.ServiceModel.SR.GetString("TraceCodeMessageClosed"), this);
}
else
{
if (!System.ServiceModel.DiagnosticUtility.ShouldTraceVerbose)
return;
TraceUtility.TraceEvent(TraceEventType.Verbose, , System.ServiceModel.SR.GetString("TraceCodeMessageClosedAgain"), this);
}
}
//Dispose模式用法
void IDisposable.Dispose()
{
//调用Close()
this.Close();
}
}

  从代码可以知道,在HttpMessage的Dispose方法里,会调用代码也是释放三种资源

  • 调用方法DisposeRequestResources释放属性字典中的待释放资源
  • 请求消息
  • 响应消息
05-11 18:13