A mutex for inter-process ;-)

[Alfred Perlstein]

One trick to handling pid wrap is to also record process
start time.  I sort of wish our signalling code allowed
this as a optional thing to make _really sure_ you weren't
signalling the wrong process.

-Alfred

* Randall Stewart <rrs at lakerest.net> [090330 16:29] wrote:
> 
> On Mar 30, 2009, at 5:16 PM, Xin LI wrote:
> 
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> >Randall Stewart wrote:
> >>Hi all:
> >>
> >>I have recently written a small set of routines that allow
> >>two process to have a "mutex" between them.. actually it allows
> >>all of the threads in any set of processes to have mutexes between
> >>themselves ;-)
> >>
> >>Anyway it seems to be working fairly well.. I still have to write a  
> >>man
> >>page
> >>for it (documentation always last).. and eventually I would like to  
> >>port in
> >>some of the WITNESS type features since the mutex's have names..
> >>
> >>I probably should also think about scaling it up a bit.. right now  
> >>its
> >>really
> >>more for a small scale (100 or less mutexes)...
> >>
> >>Who should I talk to about getting this in... having it reviewed  
> >>etc. I
> >>think
> >>it belongs in libthr since it really needs the tid of the pthreads  
> >>from the
> >>pthread_t type... and for now I have a horrible hack in to get it ;-)
> >
> >I think davidxu@ deischen@ and julian@?
> >
> >BTW.  How do you handle with one process exit (abnormally) without
> >releasing the mutex?  Just curious :)
> 
> I have a couple of ways of dealing with this..
> 
> 1) Of course the initialization routine calls atexit() to get a  
> "cleanup handler" in place.
> 2) Often times, of course, this can fail e.g. you get a SIGSEGV.. or  
> some such. When you
>    attach the memory, an audit is done. The audit will validate that  
> the pid is still alive
>    and has the particular tid in it. Of course this is not 100% but  
> as long as the tid's have
>    not rolled over it should work. The function is also public (need  
> to add that and many things
>    to the manual pages ;-D) so that one can call it whenever one  
> wants :-)
> 
> I will ping Julian and the others...
> 
> R
> 
> >
> >
> >Cheers,
> >- --
> >Xin LI <delphij at delphij.net>	http://www.delphij.net/
> >FreeBSD - The Power to Serve!
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> 
> ------------------------------
> Randall Stewart
> 803-317-4952 (cell)
> 803-345-0391(direct)
> 
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-- 
- Alfred Perlstein