How to write text to a file simultaneously from two different tasks? How to synchronize access?

To write text to a file from two different tasks (threads) in C#, it is necessary to synchronize access to the file to avoid conflicts and data corruption.

The simplest way is to use a lock object for sequential access:

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

class Program
{
    private static readonly object fileLock = new object();
    private const string filePath = "output.txt";

    static void WriteToFile(string text)
    {
        lock (fileLock)
        {
            File.AppendAllText(filePath, text + Environment.NewLine);
        }
    }

    static void Main()
    {
        Task t1 = Task.Run(() => {
            for (int i = 0; i < 10; i++)
            {
                WriteToFile($"Task 1 - Line {i}");
                Thread.Sleep(50);
            }
        });

        Task t2 = Task.Run(() => {
            for (int i = 0; i < 10; i++)
            {
                WriteToFile($"Task 2 - Line {i}");
                Thread.Sleep(50);
            }
        });

        Task.WaitAll(t1, t2);
    }
}

In this example, lock ensures that only one task writes to the file at a time, preventing simultaneous access.

Alternatively, you can use SemaphoreSlim or other synchronization mechanisms, but lock is the simplest and most effective for such cases.