C# s、 是我的。我一次又一次地看到这个问题，所以决定用最简单的方法来解决它，同时也让其他人摆脱困境：）谢谢。。这绝对有道理，帮了我大忙！您有一个输入错误：maxDegreeOfParallelismmaxDegreeOfParallelism正确的拼写确实是
C# s、 是我的。我一次又一次地看到这个问题，所以决定用最简单的方法来解决它，同时也让其他人摆脱困境：）谢谢。。这绝对有道理，帮了我大忙！您有一个输入错误：maxDegreeOfParallelismmaxDegreeOfParallelism正确的拼写确实是,c#,async-await,task-parallel-library,parallel.foreach,C#,Async Await,Task Parallel Library,Parallel.foreach,s、 是我的。我一次又一次地看到这个问题，所以决定用最简单的方法来解决它，同时也让其他人摆脱困境：）谢谢。。这绝对有道理，帮了我大忙！您有一个输入错误：maxDegreeOfParallelismmaxDegreeOfParallelism正确的拼写确实是maxDegreeOfParallelism，但是@shirandor的注释中有一些东西-在您的包中，您错误地调用了变量maxDegreeofparallism（因此，您引用的代码在更改它之前不会编译）我假设您打算从第二个代码块中的await
s、 是我的。我一次又一次地看到这个问题，所以决定用最简单的方法来解决它，同时也让其他人摆脱困境：）谢谢。。这绝对有道理，帮了我大忙！您有一个输入错误：
maxDegreeOfParallelismmaxDegreeOfParallelismawait GetData（item）awaitConcurrentBagConcurrentQueueusingtcs.SetResult（null）tcs.TrySetResult（null）信号量limCurrentCount任务IEnumerable.ToArray（）.ToList（）信号量.Wait（）等待信号量.WaitAsync（）信号量lim操作块的边界容量配置以及可等待的发送异步
方法取代。相比之下，它更有效（记忆方面）。@TheodorZoulias非常感谢您的反馈！这是我正在为一个项目积极努力的事情，所以我将关注这些变化并更新我的解决方案。@TheodorZoulias的回答显示了非常相似的方法。。。大概不会等待操作完成（我在文档中不清楚）Caleb Holt另一个您可能需要注意的问题是，枚举用户提供的enumerable
可能会导致异常，在这种情况下，您的实现将立即传播此异常，无需等待操作块的完成
。这不是一个最佳行为，因为它可能会使任务在后台运行而不被观察（以“火与忘”的方式）。正确实现ForEachAsync
方法可能相当棘手。最近我自己也意识到了这个问题。@AlexeiLevenkovSendAsync
方法的文档非常混乱。我怀疑这个星球上是否存在过一个足够聪明的人，他仅仅通过阅读文档就能理解这种方法的作用。我们应该深入研究源代码，了解Post
和SendAsync
方法都基于隐藏（显式实现）API，该API有5个可能的返回值。SendAsync
异步处理delayed
返回值。“您也可以使用async lambda”很抱歉，我不得不否决您的答案，但将异步委托传递给并行。ForEach
方法不仅仅是“不是最佳做法”。它有着深刻而无法弥补的缺陷。Parallel.ForEach
不理解异步委托，因此lambda是async void
。这不是火灾和遗忘，这是火灾和崩溃。在这种情况下，Parallel.ForEach
不会等待启动的操作完成，它不会强制执行最大程度的并行，也不会传播异常。任何异常都将无法处理，并将使流程崩溃。好吧，你不能通过展示坏例子和间接推广坏做法来期待好的投票，不管你是否推荐它们。把你的答案中所有不好的部分去掉，保留好的部分怎么样？这句话“你也可以使用异步lambda”，与Parallel.ForEach
方法联系在一起，是我无可争议的反对票。不多
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;
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;
var bag = new ConcurrentBag<object>();
var tasks = myCollection.Select(async item =>
{
// some pre stuff
var response = await GetData(item);
bag.Add(response);
// some post stuff
});
await Task.WhenAll(tasks);
var count = bag.Count;
using Dasync.Collections;
var bag = new ConcurrentBag<object>();
await myCollection.ParallelForEachAsync(async item =>
{
// some pre stuff
var response = await GetData(item);
bag.Add(response);
// some post stuff
}, maxDegreeOfParallelism: 10);
var count = bag.Count;
/// <summary>
/// Concurrently Executes async actions for each item of <see cref="IEnumerable<typeparamref name="T"/>
/// </summary>
/// <typeparam name="T">Type of IEnumerable</typeparam>
/// <param name="enumerable">instance of <see cref="IEnumerable<typeparamref name="T"/>"/></param>
/// <param name="action">an async <see cref="Action" /> to execute</param>
/// <param name="maxDegreeOfParallelism">Optional, An integer that represents the maximum degree of parallelism,
/// Must be grater than 0</param>
/// <returns>A Task representing an async operation</returns>
/// <exception cref="ArgumentOutOfRangeException">If the maxActionsToRunInParallel is less than 1</exception>
public static async Task ForEachAsyncConcurrent<T>(
this IEnumerable<T> enumerable,
Func<T, Task> action,
int? maxDegreeOfParallelism = null)
{
if (maxDegreeOfParallelism.HasValue)
{
using (var semaphoreSlim = new SemaphoreSlim(
maxDegreeOfParallelism.Value, maxDegreeOfParallelism.Value))
{
var tasksWithThrottler = new List<Task>();
foreach (var item in enumerable)
{
// Increment the number of currently running tasks and wait if they are more than limit.
await semaphoreSlim.WaitAsync();
tasksWithThrottler.Add(Task.Run(async () =>
{
await action(item).ContinueWith(res =>
{
// action is completed, so decrement the number of currently running tasks
semaphoreSlim.Release();
});
}));
}
// Wait for all tasks to complete.
await Task.WhenAll(tasksWithThrottler.ToArray());
}
}
else
{
await Task.WhenAll(enumerable.Select(item => action(item)));
}
}
await enumerable.ForEachAsyncConcurrent(
async item =>
{
await SomeAsyncMethod(item);
},
5);
public static class AsyncEx
{
public static async Task ParallelForEachAsync<T>(this IEnumerable<T> source, Func<T, Task> asyncAction, int maxDegreeOfParallelism = 10)
{
var semaphoreSlim = new SemaphoreSlim(maxDegreeOfParallelism);
var tcs = new TaskCompletionSource<object>();
var exceptions = new ConcurrentBag<Exception>();
bool addingCompleted = false;
foreach (T item in source)
{
await semaphoreSlim.WaitAsync();
asyncAction(item).ContinueWith(t =>
{
semaphoreSlim.Release();
if (t.Exception != null)
{
exceptions.Add(t.Exception);
}
if (Volatile.Read(ref addingCompleted) && semaphoreSlim.CurrentCount == maxDegreeOfParallelism)
{
tcs.TrySetResult(null);
}
});
}
Volatile.Write(ref addingCompleted, true);
await tcs.Task;
if (exceptions.Count > 0)
{
throw new AggregateException(exceptions);
}
}
}
await Enumerable.Range(1, 10000).ParallelForEachAsync(async (i) =>
{
var data = await GetData(i);
}, maxDegreeOfParallelism: 100);
var bag = new ConcurrentBag<object>();
var maxParallel = 20;
var throttler = new SemaphoreSlim(initialCount: maxParallel);
var tasks = myCollection.Select(async item =>
{
try
{
await throttler.WaitAsync();
var response = await GetData(item);
bag.Add(response);
}
finally
{
throttler.Release();
}
});
await Task.WhenAll(tasks);
var count = bag.Count;
var tasks = myCollection.Select(GetData).ToList();
await Task.WhenAll(tasks);
var results = tasks.Select(t => t.Result);
public static async Task ForEachAsyncConcurrent<T>(this IAsyncEnumerable<T> enumerable, Func<T, Task> action, int maxDegreeOfParallelism, int? boundedCapacity = null)
{
ActionBlock<T> block = new ActionBlock<T>(
action,
new ExecutionDataflowBlockOptions
{
MaxDegreeOfParallelism = maxDegreeOfParallelism,
BoundedCapacity = boundedCapacity ?? maxDegreeOfParallelism * 3
});
await foreach (T item in enumerable)
{
await block.SendAsync(item).ConfigureAwait(false);
}
block.Complete();
await block.Completion;
}
var options = new ParallelOptions { MaxDegreeOfParallelism = 5 }
Task.Run(() =>
{
Parallel.ForEach(myCollection, options, item =>
{
DoWork(item);
}
}
public static async Task ParallelForEachAsync<T>(this IEnumerable<T> source, Func<T, Task> asyncAction, int maxDegreeOfParallelism)
{
var throttler = new SemaphoreSlim(initialCount: maxDegreeOfParallelism);
var tasks = source.Select(async item =>
{
await throttler.WaitAsync();
try
{
await asyncAction(item).ConfigureAwait(false);
}
finally
{
throttler.Release();
}
});
await Task.WhenAll(tasks);
}