问题描述
在循环中，我正在使用Task.Run（// ...）创建一个任务。每个任务都包含一个WebRequest。在Task.WaitAll处，一个任务的结果被另一个任务的结果覆盖。我在做什么错？ 当尝试使用调试器时，它可以正常工作。是因为并发吗？如何解决呢？ 以下是我的代码段：
SomeMethod()
{
//someItemList.Count() == 5
int r = 0;
Task<MyModel>[] myTaskList= new Task<MyModel>[5];
foreach(var item in someItemList){
Task<MyModel> t = Task<MyModel>.Run(() => { return
SomeOperationWithWebRequest(item); });
myTaskList[r] = t;
r++;
}
Task.WaitAll(myTaskList); //myTaskList[0].Result...myTaskList[4].Result all are having same output.
}
MyModel SomeOperationwithWebRequest(Item){
string URL = "SomeURLFromItem";
string DATA = "DATAfromItem"
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(URL);
request.Method = "POST";
request.ContentType = "application/json";
request.ContentLength = DATA.Length;
using (Stream webStream = request.GetRequestStream())
using (StreamWriter requestWriter = new StreamWriter(webStream,System.Text.Encoding.ASCII))
{
requestWriter.Write(DATA);
}
try
{
WebResponse webResponse = request.GetResponseAsync();
using (Stream webStream = webResponse.GetResponseStream() ?? Stream.Null)
using (StreamReader responseReader = new StreamReader(webStream))
{
//response
}
catch (Exception ex)
{
}
return new MyModel() { // properties
};
}
解决方法
我认为它可以在调试中使用，因为您不必等待异步WebRequest。试试这个：
private readonly List<string> _someItemList = new List<string> { "t1","t2","t3" };
private async Task SomeMethodAsync()
{
var myTaskList = new List<Task<MyModel>>();
int counter = 0;
foreach (var item in _someItemList)
{
var t = Task.Run(() => SomeOperationWithWebRequestAsync(counter++));
myTaskList.Add(t);
}
await Task.WhenAll(myTaskList);
}
public async Task<MyModel> SomeOperationWithWebRequestAsync(int counter)
{
//do your async request,for simplicity I just do a delay
await Task.Delay(counter * 1000);
return new MyModel {Counter = counter };
}
public class MyModel
{
public int Counter { get; set; }
}
并像这样使用它：
await SomeMethodAsync();
还要注意Task.WhenAll与Task.WaitAll参见例如 WaitAll vs WhenAll