任务并行库中的线程数限制 [英] Limit number of Threads in Task Parallel Library

问题描述

我有几百个文件需要上传到Azure Blob存储。

我想使用并行任务库。

但是不必运行所有100个线程来上传在文件列表中的foreach中，我如何限制它可以使用的最大线程数并并行完成作业。
还是自动平衡？

I have few hundreds of files i need to upload to Azure Blob Storage.
I want to use parallel task library.
But instead of running all the 100 threads to upload in a foreach on list of files, how can i put a limit on max number of threads that it can use and finish the job in parallel. or does it balance the things automatically?

推荐答案

您根本不应该为此使用线程。有一个基于 Task 的API，它自然是异步的： CloudBlockBlob.UploadFromFileAsync 。将其与 async / await 和 SemaphoreSlim 配合使用可限制并行上传的数量。

You should not be using threads for this at all. There's a Task-based API for this, which is naturally asynchronous: CloudBlockBlob.UploadFromFileAsync. Use it with async/await and SemaphoreSlim to throttle the number of parallel uploads.

示例（未经测试）：

const MAX_PARALLEL_UPLOADS = 5;

async Task UploadFiles()
{
    var files = new List<string>();
    // ... add files to the list

    // init the blob block and
    // upload files asynchronously
    using (var blobBlock = new CloudBlockBlob(url, credentials))
    using (var semaphore = new SemaphoreSlim(MAX_PARALLEL_UPLOADS))
    {
        var tasks = files.Select(async(filename) => 
        {
            await semaphore.WaitAsync();
            try
            {
                await blobBlock.UploadFromFileAsync(filename, FileMode.Create);
            }
            finally
            {
                semaphore.Release();
            }
        }).ToArray();

        await Task.WhenAll(tasks);
    }
}

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