Re: Locking a mutex by name?

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

On Fri, Nov 14, 2008 at 7:04 PM, Ron <ron () skullsecurity net> wrote:
> Patrick Donnelly wrote:
> > On Fri, Nov 14, 2008 at 6:07 PM, Ron <ron () skullsecurity net> wrote:
> >
> > 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
>
> Good point, I wasn't thinking of it that way.
>
> It still feels cleaner, to me, for the SMB library to look after it,
> simply because there will always need to be a lock when SMB is being
> used, and only for the parts of the script while a SMB transaction is
> going on. This also ensures that programmers don't forget to lock the
> mutex when writing scripts (since they won't notice the issue until
> running multiple scripts simultaneously).
>
> My thought is that the nselib is a better place for it.

Yes, in the case of a library that is best.

As for storing the mutexes for a library, placing them in the registry
feels very wrong to me.

I've looked at the smb library in nselib/smb.lua. Right now it appears
the library has a global lock, so only on smb connection can be active
at a time? So instead you want the mutexes on a per-host basis? If
this is the case, I recommend using a local mutexes table , with smb
connection keys and mutex values, that holds the mutexes for you for
each smb connection. The table will have weak keys so an smb
connection can be collected (and thus the mutex as well). Each mutex
will still be passed the "SMB-hostname" string so you can ensure only
one smb connection per host. I've attached a patch that does this.

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

Attachment: smb_mutex.patch
Description:

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