Date: Tue, 31 Mar 2009 11:11:02 -0400 From: Randall Stewart <rrs@lakerest.net> To: John Baldwin <jhb@freebsd.org> Cc: threads@freebsd.org, freebsd-threads@freebsd.org Subject: Re: WITNESS for pthreads Message-ID: <F0D957B2-E451-4F83-8C30-4A73140470B6@lakerest.net> In-Reply-To: <200903311038.43401.jhb@freebsd.org> References: <7D4F6788-0F12-4863-9635-7FADA9115D16@lakerest.net> <9157F968-5CCF-451C-9BA0-E12A957D6B38@lakerest.net> <Pine.GSO.4.64.0903310235580.5671@sea.ntplx.net> <200903311038.43401.jhb@freebsd.org>
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This was one of the places I was heading (as I wrote privately to
Daniel ;-D)
I suppose I can share it all i.e. the pthread mutex stuff
will of course work with shared mutexe's but it won't:
a) Build an easy to use semantic for the app to agree on sharing
memory.. i.e. you
have left undefined how the process figure out what they are
sharing. There is
some value in setting up a easy semantic for app dev's to use.
<i.e. insert the mmap and all the other goo through an additional
interface>
b) What happens when a process exits or hits a core dump while holding
one
of these mutex's? Is this what you are thinking the PROCESS_SHARED
would
do??
<i.e. I don't think a process by itself can fully solve this... maybe
the
PROCESS_SHARED could be made to help here>
c) If you build something to do <a> so you have some nice way of naming
mutex's you can do something similar to our WITNESS option in the
kernel... this is something the few times I have played in user
space recently that I have missed... having LOR warnings and such
can be a useful tool. You can't have this without <a> IMO.
I was am interested in a/b but one of my long term intents is to do
<c> ;-)
R
On Mar 31, 2009, at 10:38 AM, John Baldwin wrote:
> On Tuesday 31 March 2009 2:50:27 am Daniel Eischen wrote:
>>> Ok, I have poked around at these... all the mutex attributes
>>> defined here
>>> do is set the attributes to shared. There does not seem to be any
>>> standard
>>> naming mechanism.
>>
>> Naming mechanism for what? Names shouldn't be needed for anything,
>> nor do I think it is desired.
>
> Off topic: names would be very helpful to port witness to pthreads.
> The
> thoughts I have had for doing this though would be to add a new _np
> attribute
> to set the name. I actually would like to write a 'libwitness' that
> basically overrides the various symbols and provides the name_np
> attribute
> and implement witness in the shared library on top of whatever
> pthreads
> library is in use. This would also allow it to be portable to other
> OS's.
> (Well, it could break pshared mutexes, but using the pointer-style
> types, you
> could have the libwitness allocate its own "mutex" structure which has
> a "real" mutex inside of it along with the name and other per-lock
> data it
> tracks. It would then forward mutex operations to the real pthreads
> library
> after performing LOR checks, etc.).
>
> --
> John Baldwin
>
------------------------------
Randall Stewart
803-317-4952 (cell)
803-345-0391(direct)
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