从异步调用收集响应时使用的数据结构

Question

我正在我的应用程序中运行这段代码。

public Task<BulkResponse<JObject>> GetRelatedObjectsAsync(IEnumerable<PrimaryObjectInfo> primaryObjectInfos)
{
    var allSecondaries = new List<Tuple<int, List<JObject>>>();
    var exceptionsDict = new ConcurrentDictionary<int, Exception>();

    var relatedObjectsTasks = primaryObjectInfos.Select(async primaryObjectInfo =>
    {
        try
        {
            var secondaryObject = await objectManager.GetRelatedObjectsAsync(primaryObjectInfo);
            allSecondaries.Add(Tuple.Create(primaryObjectInfo.Index, secondaryObject.ToList()));
        }
        catch (Exception ex)
        {
            exceptionsDict.TryAdd(primaryObjectInfo.Index,  ex);
        }
    });

    await Task.WhenAll(relatedObjectsTasks);

    return ConvertToBulkResponse(allSecondaries, exceptionsDict);
}

当我运行这个代码时，allSecondaries对象有时返回有效的结果列表，有时代码会捕获每个primaryObjectInfo的并行线程的异常。

异步方法objectManager.GetRelatedObjectsAsync()内部调用4-5异步函数，有些函数通过引用传递参数。(参考关键词)

问题：是否使用正确的数据结构来合并所有并行线程的结果？如果是的话，我每次得到不同结果的原因是什么？

Answer 1

您最好将执行与结果收集分开：

public Task<BulkResponse<JObject>> GetRelatedObjectsAsync(
    IEnumerable<PrimaryObjectInfo> primaryObjectInfos)
{
    var relatedObjectsTasks = primaryObjectInfos
        .Select(
            async primaryObjectInfo =>
                (primaryObjectInfo.Index,
                 await objectManager.GetRelatedObjectsAsync(primaryObjectInfo)))
        .ToList();

    try
    {
        await Task.WhenAll(relatedObjectsTasks);
    }
    catch
    {
        // observe each task's, exception
    }

    var allSecondaries = new List<(int index, List<JObject> related)>();
    var exceptionsDict = new Dictionary<int, Exception>();

    foreach (var relatedObjectsTask in relatedObjectsTasks)
    {
        try
        {
            allSecondaries.Add(relatedObjectsTask.Result);
        }
        catch (Exception ex)
        {
            exceptionsDict.Add(relatedObjectsTask.index,  ex);
        }
    }

    return ConvertToBulkResponse(allSecondaries, exceptionsDict);
}

您可以查看每个任务的IsFaulted/Exception和IsCancelled属性，而不是引发异常：

    foreach (var relatedObjectsTask in relatedObjectsTasks)
    {
        if (relatedObjectsTask.IsCancelled)
        {
            exceptionsDict.Add(
                relatedObjectsTask.index,
                new TaskCancelledException(relatedObjectsTask));
        }
        else if (relatedObjectsTask.IsFaulted)
        {
            exceptionsDict.TryAdd(relatedObjectsTask.index,  ex);
        }
        else
        {
            allSecondaries.Add(relatedObjectsTask.Result);
        }
    }