Re: Locking a mutex by name?

["Patrick Donnelly" <batrick.donnelly () gmail com>]

On Fri, Nov 14, 2008 at 6:07 PM, Ron <ron () skullsecurity net> wrote:
> Patrick Donnelly wrote:
> > On Fri, Nov 14, 2008 at 5:04 PM, Ron <ron () skullsecurity net> wrote:
> >
> > The problem you are experiencing is the mutex is being garbage
> > collected during the time between you lock it and release it. The
> > mutexes are stored internally with weak references to allow them to be
> > collected when no longer used. The registry is holding onto that
> > reference for you. It is normally expected you use a local reference
> > to the mutex. I would recommend you not store the reference in the
> > registry and instead keep it local or in the function's (that is, your
> > script) environment.
>
> Ah, that would explain the behaviour.
>
> The issue is that multiple scripts need to use the same mutex. If there
> are three scripts using SMB against a single host, they need to run
> individually. Due to a "feature" in Windows, you can't make more than
> one SMB connection at the same time from the same IP.
>
> Do you think that storing them in the registry is a good bet, or do you
> see a better way of doing mutexes on a global level?

You really only need to worry that the thread using the mutex keeps a
reference to it from the point it locks it to the point it releases
it. How you decide to keep the reference is up to you. It could be as
simple as:

local mutex;

-- ... other code

function action(host, port)
  mutex = nmap.mutex("SMB-"..host.ip);
  -- do stuff...
end

Cheers,

-- 
-Patrick Donnelly

"One of the lessons of history is that nothing is often a good thing
to do and always a clever thing to say."

-Will Durant

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