相关疑难解决方法(0)

在metro应用程序中,我需要执行许多WCF调用.有大量的调用,所以我需要在并行循环中进行调用.问题是并行循环在WCF调用完成之前退出.

你会如何重构这个按预期工作？

var ids = new List<string>() { "1", "2", "3", "4", "5", "6", "7", "8", "9", "10" };
var customers = new  System.Collections.Concurrent.BlockingCollection<Customer>();

Parallel.ForEach(ids, async i =>
{
    ICustomerRepo repo = new CustomerRepo();
    var cust = await repo.GetCustomer(i);
    customers.Add(cust);
});

foreach ( var customer in customers )
{
    Console.WriteLine(customer.ID);
}

Console.ReadKey();

我想并行处理一个集合,但是我在实现它时遇到了麻烦,因此我希望得到一些帮助.

如果我想在并行循环的lambda中调用C#中标记为async的方法,则会出现问题.例如:

var bag = new ConcurrentBag<object>();
Parallel.ForEach(myCollection, async item =>
{
  // some pre stuff
  var response = await GetData(item);
  bag.Add(response);
  // some post stuff
}
var count = bag.Count;

计数为0时会出现问题,因为创建的所有线程实际上只是后台线程,并且Parallel.ForEach调用不等待完成.如果我删除async关键字,该方法如下所示:

var bag = new ConcurrentBag<object>();
Parallel.ForEach(myCollection, item =>
{
  // some pre stuff
  var responseTask = await GetData(item);
  responseTask.Wait();
  var response = responseTask.Result;
  bag.Add(response);
  // some post stuff
}
var count = bag.Count;

它工作,但它完全禁用等待聪明,我必须做一些手动异常处理..(为简洁起见删除).

如何实现一个Parallel.ForEach在lambda中使用await关键字的循环？可能吗？

Parallel.ForEach方法的原型采用Action<T>as参数,但我希望它等待我的异步lambda.

我正在尝试将Stephen Toub 的 ForEachAsync<T>扩展方法更改为返回结果的扩展......

斯蒂芬的扩展：

public static Task ForEachAsync<T>(this IEnumerable<T> source, int dop, Func<T, Task> body) 
{ 
    return Task.WhenAll( 
        from partition in Partitioner.Create(source).GetPartitions(dop) 
        select Task.Run(async delegate { 
            using (partition) 
                while (partition.MoveNext()) 
                    await body(partition.Current); 
        })); 
}

我的方法（不起作用；任务被执行但结果是错误的）

public static Task<TResult[]> ForEachAsync<T, TResult>(this IList<T> source,
    int degreeOfParallelism, Func<T, Task<TResult>> body)
{
    return Task.WhenAll<TResult>(
        from partition in Partitioner.Create(source).GetPartitions(degreeOfParallelism)
        select Task.Run<TResult>(async () = 
        {
            using (partition)
                while (partition.MoveNext())
                    await body(partition.Current); // When I "return await",
                        // I get good results but only …