Question

The Mutex class is very misunderstood, and Global mutexes even more so.

What is good, safe pattern to use when creating Global mutexes?

One that will work

• Regardless of the locale my machine is in
• Is guaranteed to release the mutex properly
• Optionally does not hang forever if the mutex is not acquired
• Deals with cases where other processes abandon the mutex

Answer 1

I want to make sure this is out there, because it’s so hard to get right:

using System.Runtime.InteropServices;   //GuidAttribute using System.Reflection;                //Assembly using System.Threading;                 //Mutex using System.Security.AccessControl;    //MutexAccessRule using System.Security.Principal;        //SecurityIdentifier  static void Main(string[] args) {     // get application GUID as defined in AssemblyInfo.cs     string appGuid =         ((GuidAttribute)Assembly.GetExecutingAssembly().             GetCustomAttributes(typeof(GuidAttribute), false).                 GetValue(0)).Value.ToString();      // unique id for global mutex - Global prefix means it is global to the machine     string mutexId = string.Format( 'Global\\{{{0}}}', appGuid );      // Need a place to store a return value in Mutex() constructor call     bool createdNew;      // edited by Jeremy Wiebe to add example of setting up security for multi-user usage     // edited by 'Marc' to work also on localized systems (don't use just 'Everyone')      var allowEveryoneRule =         new MutexAccessRule( new SecurityIdentifier( WellKnownSidType.WorldSid                                                    , null)                            , MutexRights.FullControl                            , AccessControlType.Allow                            );     var securitySettings = new MutexSecurity();     securitySettings.AddAccessRule(allowEveryoneRule);     // edited by MasonGZhwiti to prevent race condition on security settings via VanNguyen     using (var mutex = new Mutex(false, mutexId, out createdNew, securitySettings))     {         // edited by acidzombie24         var hasHandle = false;         try         {             try             {                 // note, you may want to time out here instead of waiting forever                 // edited by acidzombie24                 // mutex.WaitOne(Timeout.Infinite, false);                 hasHandle = mutex.WaitOne(5000, false);                 if (hasHandle == false)                     throw new TimeoutException('Timeout waiting for exclusive access');             }             catch (AbandonedMutexException)             {                 // Log the fact that the mutex was abandoned in another process,                 // it will still get acquired                 hasHandle = true;             }              // Perform your work here.         }         finally         {             // edited by acidzombie24, added if statement             if(hasHandle)                 mutex.ReleaseMutex();         }     } }