如何为同时运行的多个ActionBlock设置CPU优先级？

Question

我有一堆ActionBlocks，每个都做不同的事情。

• 大者处理数据，并通过TransformBlock连续地馈入数据。
• 另外3个ActionBlocks只需在3个文本文件（日志）中写行。

这很有效，除了3个日志记录ActionBlocks仅在处理ActionBlock完成后才开始使用数据（因此，它们在程序末尾一次性写入所有日志记录信息。

我想知道是否可以影响此行为，以便为日志记录ActionBlocks赋予更高的优先级？

感谢您的帮助。

代码示例：

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using System.Threading.Tasks.Dataflow;

namespace dataflowtest
{
    class Program
    {
        const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        static readonly IReadOnlyCollection<string> charsSets = Enumerable.Repeat(chars, 8).ToList().AsReadOnly();
        static readonly Random random = new Random();

        static event EventHandler<string> MessageGot;

        static async Task Main(string[] args)
        {
            var source = new TransformBlock<string, string>(GetMessage, new ExecutionDataflowBlockOptions { MaxDegreeOfParallelism = -1, EnsureOrdered = false });
            var target = new ActionBlock<string>(Console.WriteLine);


            var programDir = Path.GetDirectoryName(System.Reflection.Assembly.GetEntryAssembly().GetName().CodeBase.Replace("file:///", ""));
            using var file1 = new StreamWriter(Path.Combine(programDir, "file1.txt"));
            using var file2 = new StreamWriter(Path.Combine(programDir, "file2.txt"));
            using var file3 = new StreamWriter(Path.Combine(programDir, "file3.txt"));

            var fileAction1 = new ActionBlock<string>(file1.WriteLineAsync);
            var fileAction2 = new ActionBlock<string>(file2.WriteLineAsync);
            var fileAction3 = new ActionBlock<string>(file3.WriteLineAsync);

            MessageGot += async (_, e) => await fileAction1.SendAsync(e);
            MessageGot += async (_, e) => await fileAction2.SendAsync(e);
            MessageGot += async (_, e) => await fileAction3.SendAsync(e);

            using (source.LinkTo(target, new DataflowLinkOptions { PropagateCompletion = true }))
            {
                for (int i = 0; i < 100; i++)
                {
                    await source.SendAsync(i.ToString() + '\t' + new string(charsSets.Select(s => s[random.Next(s.Length)]).ToArray()));
                }

                source.Complete();
                await target.Completion;
            }
        }

        private static async Task<string> GetMessage(string input)
        {
            int delay = random.Next(25, 6000);
            await Task.Delay(delay);
            string message = input.ToLowerInvariant() + '\t' + delay.ToString();

            MessageGot?.Invoke(null, message);

            return message;
        }
    }
}

Answer 1

默认情况下，StreamWriter将每4,096字节刷新其缓冲区。您可能希望它在写入的每一行上都刷新。所以代替这个：

var fileAction1 = new ActionBlock<string>(file1.WriteLineAsync);

...执行此操作：

var fileAction1 = new ActionBlock<string>(item =>
{
    file1.WriteLine(item);
    file1.Flush();
});

使用WriteLineAsync而不是WriteLine没有好处，因为尚未使用FileStream选项打开基础FileOptions.Asynchronous。