如何正确地并行运行多个异步任务？

Question

如果您需要并行运行多个异步I/O任务但需要确保不会同时运行多个XI/O进程,该怎么办？I/O处理前后的任务不应该有这样的限制.

这是一个场景 - 假设有1000个任务; 每个人都接受一个文本字符串作为输入参数; 转换该文本(预I/O处理)然后将转换后的文本写入文件.目标是使预处理逻辑利用100%的CPU /内核和任务的I/O部分以最大10度并行性运行(同时打开最多10个用于一次写入文件).

你能提供一个示例代码如何使用C#/ .NET 4.5吗？

http://blogs.msdn.com/b/csharpfaq/archive/2012/01/23/using-async-for-file-access-alan-berman.aspx

Answer 1

我认为使用TPL Dataflow是一个好主意:您创建具有无限并行性的前后处理块,具有有限并行性的文件写入块并将它们链接在一起.就像是:

var unboundedParallelismOptions =
    new ExecutionDataflowBlockOptions
    {
        MaxDegreeOfParallelism = DataflowBlockOptions.Unbounded
    };

var preProcessBlock = new TransformBlock<string, string>(
    s => PreProcess(s), unboundedParallelismOptions);

var writeToFileBlock = new TransformBlock<string, string>(
    async s =>
            {
                await WriteToFile(s);
                return s;
            },
    new ExecutionDataflowBlockOptions { MaxDegreeOfParallelism = 10 });

var postProcessBlock = new ActionBlock<string>(
    s => PostProcess(s), unboundedParallelismOptions);

var propagateCompletionOptions =
    new DataflowLinkOptions { PropagateCompletion = true };

preProcessBlock.LinkTo(writeToFileBlock, propagateCompletionOptions);
writeToFileBlock.LinkTo(postProcessBlock, propagateCompletionOptions);

// use something like await preProcessBlock.SendAsync("text") here

preProcessBlock.Complete();
await postProcessBlock.Completion;

哪里WriteToFile()可能是这样的:

private static async Task WriteToFile(string s)
{
    using (var writer = new StreamWriter(GetFileName()))
        await writer.WriteAsync(s);
}