How to open a file for non-exclusive write access using .NET

Question

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.

Edit: 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.

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;
        }
    }
}

Answer 1

Use the FileShare enumeration when opening the file using File.Open. Specifically, use FileShare.ReadWrite.