[Mono-dev] Mutex Bug

[Zoltan Varga]

Hi,

  mono used to support this functionality, but the code to do that was very
problematic, and it is disabled in recent mono releases.

           Zoltan


On Wed, Jul 2, 2014 at 9:31 PM, Edward Ned Harvey (mono) <
edward.harvey.mono at clevertrove.com> wrote:

> Before anything else ...  Can anybody recommend a way to do interprocess
> mutex?
>
> I would like to confirm this is a bug before I go create a bug report in
> bugzilla.  Can anybody please confirm both (a) you get the same behavior,
> and (b) it's not correct behavior?
>
> I want to make this observation as well:  The class in question is
> System.Threading.Mutex.  But on the mono class status pages, there seems to
> be no System.Threading.Mutex.  So that sounds a little suspicious to me,
> but maybe it's ok?  Or maybe I'm overlooking it somehow?
>
> Here is some sample source code:
> using System;
> using System.Threading;
>
> namespace FunWithMutex
> {
>     class MainClass
>     {
>         static string mutexName;
>         const int numThreads = 5;
>         static Thread[] allThreads = new Thread[numThreads];
>         public static void Main(string[] args)
>         {
>             mutexName = @"Global\mutex-test-erihjbnkjvwiuehrnkjcxvjhwehiu";
>             for (int i=0; i<numThreads; i++)
>             {
>                 allThreads[i] = new Thread(new ThreadStart(DoSomething));
>                 allThreads[i].Name = "Thread #" + i.ToString();
>                 allThreads[i].Start();
>             }
>         }
>         static void DoSomething()
>         {
>             System.Console.Error.WriteLine(Thread.CurrentThread.Name + "
> starting...");
>             using (var myMutex = new Mutex(false,mutexName))
>             {
>                 myMutex.WaitOne();
>                 try
>                 {
>                     System.Console.Error.WriteLine(
> Thread.CurrentThread.Name + " running...");
>                     Thread.Sleep(TimeSpan.FromSeconds(5));
>                     System.Console.Error.WriteLine(
> Thread.CurrentThread.Name + " finished...");
>                 }
>                 finally
>                 {
>                     myMutex.ReleaseMutex();
>                 }
>             }
>         }
>     }
> }
>
>
> When run in windows .NET, you launch several processes that each run the
> above code, and the Mutex will only allow one process to enter at a time.
>
> When run in Mono, a single process obeys the mutex correctly, but multiple
> processes that are launched concurrently, each have an apparently private
> mutex, because each process will allow a single thread to enter the mutex
> concurrently.
>
> In other words, the mutex *should* provide synchronization across multiple
> processes, but it doesn't.  Instead, it only provides synchronization
> across multiple threads within a single process.
>
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>
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