Sam Saffron Sam Saffron - 1 year ago 118
C# Question

What is a good pattern for using a Global Mutex in C#?

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 Source

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 =
            GetCustomAttributes(typeof(GuidAttribute), false).

    // 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();

    // 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;
                // 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.
            // edited by acidzombie24, added if statement
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