如何使用.NET打开文件以进行非排他性写访问 [英] How to open a file for non-exclusive write access using .NET
问题描述
是否可以在具有非独占写访问权限的.NET中打开文件?如果是这样,怎么办?我希望有两个或多个进程同时写入同一文件.
Is it possible to open a file in .NET with non exclusive write access? If so, how? My hope is to have two or more processes write to the same file at the same time.
:这是此问题的上下文:我正在为IIS写一个简单的日志记录HTTPModule.由于在不同应用程序池中运行的应用程序作为不同的进程运行,因此我需要一种在进程之间共享日志文件的方法.我可以编写一个复杂的文件锁定例程,也可以编写一个懒惰的编写器,但这是一个废弃项目,因此并不重要.
Here is the context of this question: I am writing a simple logging HTTPModule for IIS. Since applications running in different app pools run as distinct processes, I need a way to share the log file between processes. I could write a complex file locking routine, or a lazy writer, but this is a throw away project so its not important.
这是我用来弄清楚该过程的测试代码.
This is the test code I used to figure out the process.
using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Threading;
namespace FileOpenTest
{
class Program
{
private static bool keepGoing = true;
static void Main(string[] args)
{
Console.CancelKeyPress += new ConsoleCancelEventHandler(Console_CancelKeyPress);
Console.Write("Enter name: ");
string name = Console.ReadLine();
//Open the file in a shared write mode
FileStream fs = new FileStream("file.txt",
FileMode.OpenOrCreate,
FileAccess.ReadWrite,
FileShare.ReadWrite);
while (keepGoing)
{
AlmostGuaranteedAppend(name, fs);
Console.WriteLine(name);
Thread.Sleep(1000);
}
fs.Close();
fs.Dispose();
}
private static void AlmostGuaranteedAppend(string stringToWrite, FileStream fs)
{
StreamWriter sw = new StreamWriter(fs);
//Force the file pointer to re-seek the end of the file.
//THIS IS THE KEY TO KEEPING MULTIPLE PROCESSES FROM STOMPING
//EACH OTHER WHEN WRITING TO A SHARED FILE.
fs.Position = fs.Length;
//Note: there is a possible race condition between the above
//and below lines of code. If a context switch happens right
//here and the next process writes to the end of the common
//file, then fs.Position will no longer point to the end of
//the file and the next write will overwrite existing data.
//For writing periodic logs where the chance of collision is
//small, this should work.
sw.WriteLine(stringToWrite);
sw.Flush();
}
private static void Console_CancelKeyPress(object sender, ConsoleCancelEventArgs e)
{
keepGoing = false;
}
}
}
推荐答案
使用 FileShare 枚举.具体来说,请使用FileShare.ReadWrite.
Use the FileShare enumeration when opening the file using File.Open. Specifically, use FileShare.ReadWrite.
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