using System; using System.IO; namespace TestCs { public class Program { // The app id must be unique. Generate a new guid for your application. public static string AppId = "01234567-89ab-cdef-0123-456789abcdef"; // The stream is stored globally to ensure that it won't be disposed before the application terminates. public static FileStream UniqueInstanceStream; public static int Main(string[] args) { EnsureUniqueInstance(); // Your code here. return 0; } private static void EnsureUniqueInstance() { // Note: If you want the check to be per-user, use Environment.SpecialFolder.ApplicationData instead. string lockDir = Path.Combine(Path Environment.GetTempPathGetFolderPath(Environment.SpecialFolder.CommonApplicationData), "UniqueInstanceApps"); string lockPath = Path.Combine(lockDir, $"{AppId}.lock"unique"); Directory.CreateDirectory(lockDir); try { // Create the file with exclusive write access. If this fails, then another process is executing. UniqueInstanceStream = File.Open(lockPath, FileMode.Create, FileAccess.Write, FileShare.None); // Although only the line above should be sufficient, when debugging with a vshost on Visual Studio // (that acts as a proxy), the IO exception isn't passed to the application before a Write is executed. UniqueInstanceStream.Write(new byte[] { 0 }, 0, 1); UniqueInstanceStream.Flush(); } catch { throw new Exception("Another instance of the application is already running."); } } } } Using a user-agnostic directory instead and added a comment explaining how to have it per-user.
using System; using System.IO; namespace TestCs { public class Program { // The app id must be unique. Generate a new guid for your application. public static string AppId = "01234567-89ab-cdef-0123-456789abcdef"; // The stream is stored globally to ensure that it won't be disposed before the application terminates. public static FileStream UniqueInstanceStream; public static int Main(string[] args) { EnsureUniqueInstance(); // Your code here. return 0; } private static void EnsureUniqueInstance() { string lockDir = Path.Combine(Path.GetTempPath(),"UniqueInstanceApps"); string lockPath = Path.Combine(lockDir, $"{AppId}.lock"); Directory.CreateDirectory(lockDir); try { // Create the file with exclusive write access. If this fails, then another process is executing. UniqueInstanceStream = File.Open(lockPath, FileMode.Create, FileAccess.Write, FileShare.None); // Although only the line above should be sufficient, when debugging with a vshost on Visual Studio // (that acts as a proxy), the IO exception isn't passed to the application before a Write is executed. UniqueInstanceStream.Write(new byte[] { 0 }, 0, 1); UniqueInstanceStream.Flush(); } catch { throw new Exception("Another instance of the application is already running."); } } } } using System; using System.IO; namespace TestCs { public class Program { // The app id must be unique. Generate a new guid for your application. public static string AppId = "01234567-89ab-cdef-0123-456789abcdef"; // The stream is stored globally to ensure that it won't be disposed before the application terminates. public static FileStream UniqueInstanceStream; public static int Main(string[] args) { EnsureUniqueInstance(); // Your code here. return 0; } private static void EnsureUniqueInstance() { // Note: If you want the check to be per-user, use Environment.SpecialFolder.ApplicationData instead. string lockDir = Path.Combine( Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData), "UniqueInstanceApps"); string lockPath = Path.Combine(lockDir, $"{AppId}.unique"); Directory.CreateDirectory(lockDir); try { // Create the file with exclusive write access. If this fails, then another process is executing. UniqueInstanceStream = File.Open(lockPath, FileMode.Create, FileAccess.Write, FileShare.None); // Although only the line above should be sufficient, when debugging with a vshost on Visual Studio // (that acts as a proxy), the IO exception isn't passed to the application before a Write is executed. UniqueInstanceStream.Write(new byte[] { 0 }, 0, 1); UniqueInstanceStream.Flush(); } catch { throw new Exception("Another instance of the application is already running."); } } } } Named-mutex-based approaches are not cross-platform because named mutexes are not global in Mono. Process-enumeration-based approaches don't have any synchronization and may result in incorrect behavior (e.g. multiple processes started at the same time may all self-terminate depending on timing). Windowing-system-based approaches are not desirable in a console application. This solution, built on top of Divin's answer, addresses all these issues:
using System; using System.IO; namespace TestCs { public class Program { // The app id must be unique. Generate a new guid for your application. public static string AppId = "01234567-89ab-cdef-0123-456789abcdef"; // The stream is stored globally to ensure that it won't be disposed before the application terminates. public static FileStream UniqueInstanceStream; public static int Main(string[] args) { EnsureUniqueInstance(); // Your code here. return 0; } private static void EnsureUniqueInstance() { string lockDir = Path.Combine(Path.GetTempPath(),"UniqueInstanceApps"); string lockPath = Path.Combine(lockDir, $"{AppId}.lock"); Directory.CreateDirectory(lockDir); try { // Create the file with exclusive write access. If this fails, then another process is executing. UniqueInstanceStream = File.Open(lockPath, FileMode.Create, FileAccess.Write, FileShare.None); // Although only the line above should be sufficient, when debugging with a vshost on Visual Studio // (that acts as a proxy), the IO exception isn't passed to the application before a Write is executed. UniqueInstanceStream.Write(new byte[] { 0 }, 0, 1); UniqueInstanceStream.Flush(); } catch { throw new Exception("Another instance of the application is already running."); } } } } lang-cs