Mutex means mutual exclusion. Mutex is class in .NET framework. It is thread synchronization process. Mutex is used to prevent the execution of a shared resource by multiple threads. It allows only one single thread to enter to execute a particular task. It is used in single process or multiple processes. It can also be used for inter-process synchronization. Monitor/Lock prevents shared resource from internal threads, but Mutex prevent from both internal as well as external threads. In another way we can say, mutex provide thread safety against internal/external threads.
Example: Multiple threads are writing to file in this example.
I have synchronization multiple thread using mutex. Only one thread is accessing shared resource (file here) at a time.
using System;
using System.Threading;
using System.IO;
public class ConsoleApplication1
{
public static void Main(string[] args)
{
for (int i = 0; i < 5; i++)
{
Thread thread = new Thread(new ThreadStart(Go));
thread.Name = String.Concat("Thread ", i);
thread.Start();
}
Console.ReadLine();
}
public static void Go()
{
Thread.Sleep(500);
WriteFile();
}
static Mutex mutex = new Mutex();
public static void WriteFile()
{
mutex.WaitOne();
String ThreadName = Thread.CurrentThread.Name;
Console.WriteLine("{0} using resource", ThreadName);
try
{
using (StreamWriter sw = new StreamWriter("C:\\abc.txt",true))
{
sw.WriteLine(ThreadName);
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
Console.WriteLine("{0} releasing resource", ThreadName);
mutex.ReleaseMutex();
}
}
Handling single Instance of Application:
using System;
using System.Threading;
namespace ConsoleApplication1
{
class SingleInstance
{
static void Main(string[] args)
{
string appGUID="5a913d2e-1d4b-492c-a408-df315ca3de93";
bool ok;
Mutex mutex = new System.Threading.Mutex(true, appGUID, out ok);
if (!ok)
{
Console.WriteLine("Another instance is already running.");
}
else
{
Console.WriteLine("Single instance is running.");
}
Console.ReadLine();
}
}
}
When application will be launched first time, you can see below message.
When application is launched more than 1 times then you will see below message.
Conclusion:
- 1. The name of the mutex should be a unique either assembly name or GUID.
- 2. Mutex hits performance, so it should be used when synchronization across process boundaries is required.
- 3. A mutex can also be passed across application domain boundaries.