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C#: volatile

Handbook C# · Practical Guide

Defines the read and write visibility rules of a field between threads. Does not make a compound operation like counter++ atomic.

Simple example (Example.cs)

Save this example separately as Example.cs. Run it independently of the other examples on this page.

Example.cs:

// PROJECT-EXAMPLE
System.Console.WriteLine(new State().Stopped);
class State { public volatile bool Stopped = false; }

Result:

False

Syntax

private volatile bool stopping;

Example 1: simple form

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        Worker worker = new();
        await Task.Run(() => worker.Stopping = true);
        Console.WriteLine(worker.Stopping);
    }
}
public sealed class Worker { public volatile bool Stopping; }

Example 2: another practical form

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        State state = new();
        state.Publish();
        Console.WriteLine(state.IsReady);
    }
}
public sealed class State { private volatile bool ready; public bool IsReady => ready; public void Publish() { ready = true; } }

Official source: Microsoft Learn.