C#并发文件流读/写eof

Question

我有一个线程在日志文件中生成行：

var t1 = Task.Factory.StartNew(() =>
{
    using (var fileStream = File.Open(file, FileMode.Create, FileAccess.Write, FileShare.Read))
    using (var streamWriter = new StreamWriter(fileStream))
    {
        for (var i = 0; i < 10; i++)
        {
            streamWriter.WriteLine(i);
            streamWriter.Flush();
            Thread.Sleep(1000);
        }
    }

    File.Delete(file);
});

我有一个线程从同一个日志文件中读取行：

// Reads lines from the log file.
var t2 = Task.Factory.StartNew(() =>
{
    Thread.Sleep(500); // Horrible wait to ensure file existence in this test case.
    using (var fileStream = new FileStream(file, FileMode.Open, FileAccess.Read, FileShare.Delete | FileShare.Read | FileShare.Write))
    using (var streamReader = new StreamReader(fileStream))
    {
        string line;
        while ((line = streamReader.ReadLine()) != null) Console.WriteLine(line);
        // FIXME: The stream reader stops, instead of doing a continous read.
        Console.WriteLine("End of file");
    }
});

阅读器应该阅读所有写入的行，因此它应该等待更多数据，而不是在第一次遇到 EOF 时停止。我不介意读者是否永远不会“完成”，只要文件继续存在，读者就可以继续阅读。我怎样才能做到这一点？用于复制目的的完整代码：

using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;

namespace PlayGround
{
    internal static class Program
    {
        private static void Main()
        {
            const string file = "test.log";

            // Writes lines to the log file.
            var t1 = Task.Factory.StartNew(() =>
            {
                using (var fileStream = File.Open(file, FileMode.Create, FileAccess.Write, FileShare.Read))
                using (var streamWriter = new StreamWriter(fileStream))
                {
                    for (var i = 0; i < 10; i++)
                    {
                        streamWriter.WriteLine(i);
                        streamWriter.Flush();
                        Thread.Sleep(1000);
                    }
                }

                File.Delete(file);
            });

            // Reads lines from the log file.
            var t2 = Task.Factory.StartNew(() =>
            {
                Thread.Sleep(500); // Horrible wait to ensure file existence in this test case.
                using (
                    var fileStream = new FileStream(file, FileMode.Open, FileAccess.Read,
                        FileShare.Delete | FileShare.Read | FileShare.Write))
                using (var streamReader = new StreamReader(fileStream))
                {
                    string line;
                    while ((line = streamReader.ReadLine()) != null) Console.WriteLine(line);
                    // FIXME: The stream reader stops, instead of doing a continous read.
                    Console.WriteLine("End of file");
                }
            });

            Task.WaitAll(t1, t2);
        }
    }
}

编辑：作为一个实际示例，这对于第三方进程正在生成需要读取和处理的日志条目的场景很有用。如果这使应用程序和使用更清晰，您可以将其视为日志文件阅读器。

Answer 1

您可以在line == null 时执行等待，方法是检查streamReader.EndOfFile 属性。使用Thread.Sleep(1000) 不是一个理想的解决方案，有点老套，我想还有其他更好的替代解决方案。 :-)

using (var fileStream = new FileStream(file, FileMode.Open, FileAccess.Read, FileShare.Delete | FileShare.Read | FileShare.Write))
using (var streamReader = new StreamReader(fileStream))
{
    string line;
    bool running = true; // we may want to terminate this loop in some condition.
    while (running)
    {
        line = streamReader.ReadLine();
        if (line != null)
        {
            Console.WriteLine(line);
        }
        else // as per edit, the whole else block can be omitted.
        {
            while (streamReader.EndOfStream)
            {
                Thread.Sleep(1000); // wait around for n time. This could end up in an infinte loop if the file is not written to anymore. 
            }
        }
   }

   // FIXME: The stream reader stops, instead of doing a continous read.
   Console.WriteLine("End of file");
}

编辑：你可以不用 else 块：

else 
{ 
    while (streamReader.EndOfStream) 
    { 
        Thread.Sleep(1000) 
    } 
}

像这样：

while (running)
{
    line = streamReader.ReadLine();
    if (line != null)
    {
        Console.WriteLine(line);
    }
}

Answer 2

您需要同步机制，在这种情况下我使用 AutoResetEvent。 根据您的代码所需的更改是。

const string file = "test.log";
// Adds new line.
AutoResetEvent signal = new AutoResetEvent(false);

streamWriter.Flush();
// Adds new line.
signal.Set();

File.Delete(file);
// Adds new line
signal.Set();

Thread.Sleep(500);
// Replaces with.
signal.WaitOne();

while ((line = streamReader.ReadLine()) != null) Console.WriteLine(line);
// Replaces with.
while ((line = streamReader.ReadLine()) != null)
{
    signal.WaitOne();
    Console.WriteLine(line);
}

完整代码

const string file = "test.log";
AutoResetEvent signal = new AutoResetEvent(false);

// Writes lines to the log file.
var t1 = Task.Factory.StartNew(() =>
{
    using (var fileStream = File.Open(file, FileMode.Create, FileAccess.Write, FileShare.Read))
    {
        using (var streamWriter = new StreamWriter(fileStream))
        {
            for (var i = 0; i < 10; i++)
            {
                streamWriter.WriteLine(i);
                streamWriter.Flush();
                signal.Set();
                Thread.Sleep(10);
            }
        }
    }

    File.Delete(file);
    signal.Set();
});

// Reads lines from the log file.
var t2 = Task.Factory.StartNew(() =>
{
    signal.WaitOne();
    using (var fileStream = new FileStream(file, FileMode.Open, FileAccess.Read, FileShare.Delete | FileShare.Read | FileShare.Write))
    {
        using (var streamReader = new StreamReader(fileStream))
        {
            string line;
            while ((line = streamReader.ReadLine()) != null)
            {
                signal.WaitOne();
                Console.WriteLine(line);
            }

            // FIXME: The stream reader stops, instead of doing a continous read.
            Console.WriteLine("End of file");
        }
    }
});

Task.WaitAll(t1, t2);