我试图了解AsyncLocal应该如何在.Net 4.6中运行。我将一些数据放入AsyncLocal ......但是当ThreadContext更改时,它被设置为null。我使用AsyncLocal的全部原因是在等待异步操作时尝试跨线程保留/缓存此值。知道为什么会特别调用它并在上下文发生变化时设置为null吗?关于AsyncLocal的文档非常稀疏......也许我已经把它弄错了。
In [8]: res
Out[8]:
array([Decimal('1.336968892230304730842136747E-1929'),
Decimal('5.449748658873386365158990318E+1043'),
Decimal('2.310919470411918843300593208E+1276'),
Decimal('3.935786060399813919328612177E+1163'),
Decimal('5.459985199929802328950162777E+1655'),
Decimal('6.284598705467681430195924361E-2217'),
Decimal('1.144104288612524663561821431E-1280'),
Decimal('7.165867721516773886182595222E+1136'),
Decimal('1.844064027516274886503591410E+530'),
Decimal('1.596549217532394091033873077E-530')], dtype=object)
以下是如何调用它的示例。这是使用EventStore连接(GetEventStore.com)调用的异步事件订阅者。如果这里等待的两个任务没有做任何事情(如果没有要查找的ID)我没有问题,因为可能是任务同步运行。但如果我确实要完成这些任务的工作,我就失去了我的背景。
public class RequestContextProvider : IRequestContextProvider
{
private static readonly AsyncLocal<IRequestContext> _requestContext = new AsyncLocal<IRequestContext>(ValueChangedHandler);
private static void ValueChangedHandler(AsyncLocalValueChangedArgs<IRequestContext> asyncLocalValueChangedArgs)
{
**//This is just here to observe changes...when I await a call that
//causes control to pass to a different thread..this is called
//with a current value of null.**
var previousValue = asyncLocalValueChangedArgs.PreviousValue;
var currentValue = asyncLocalValueChangedArgs.CurrentValue;
var contextChanged = asyncLocalValueChangedArgs.ThreadContextChanged;
}
public void SetContext(IRequestContext requestContext)
{
_requestContext.Value = requestContext;
}
public IRequestContext GetContext()
{
return _requestContext.Value;
}
}
这是我的hacky解决方案似乎有效:
private async Task PublishProduct(Guid productId, Guid productReferenceId, IEnumerable<Guid> disclosureIds,
IEnumerable<Guid> addOnIds)
{
var disclosureReferenceIdsTask = _disclosureReferenceIdService.GetReferenceIdsAsync(disclosureIds);
var addOnReferenceIdsTask = _addOnReferenceIdService.GetReferenceIdsAsync(addOnIds);
await Task.WhenAll(disclosureReferenceIdsTask, addOnReferenceIdsTask);
IEnumerable<Guid> disclosuresResult = await disclosureReferenceIdsTask;
IEnumerable<Guid> addOnsResult = await addOnReferenceIdsTask;
await _eventPublisher.PublishAsync(new ProductPublished(productId, productReferenceId,
disclosuresResult.ToList(), addOnsResult.ToList()));
}
仅供参考,这是一个在DNX RC1下作为控制台应用程序运行的4.6运行时项目。
答案 0 :(得分:0)
您需要做的是:ExecutionContext.SuppressFlow();
当您的线程上下文丢失时,这将停止引发事件valueChangedHandler
,因此您将不会获得NULL
值,也会在创建新的ThreadContext并将数据复制到此时停止引发事件。
private static void ValueChanged(AsyncLocalValueChangedArgs<string> obj)
{
Console.WriteLine(obj.CurrentValue);
}
public static void Main(string[] args)
{
ExecutionContext.SuppressFlow();
AsyncLocalContext.Value = "Main";
Task.Run(() =>
{
AsyncLocalContext.Value = "Test1";
}).Wait();
Console.WriteLine("Main: " + AsyncLocalContext.Value);
}
输出是:
Main
Test1
Main: Main
如果我们发表评论ExecutionContext.SuppressFlow();
,那么就会得到:
Main
Main -- copied data to Task
Test1
-- here is NULL when context has lost
Main: Main