[sr-dev] shm_regex deadlock

[Miklos Tirpak]

Hi,

Stefan, thank you very much for the patch!
In general, you should use this library only if you really need posix 
regular expressions in shared memory. If you are fine with the perl 
syntax then I would rather suggest pcre. Pcre can allocate the memory in 
a single block that can be moved to shm mem easily.
I made some performance tests a year ago with simple expressions, the 
libc implementation and pcre performed almost at the same speed when 
back tracking was not in use. With back tracking, pcre was an order of 
magnitude faster than libc.

Henning, I can apply the patch, will do that asap. Thanks for the pointer!

Thanks,
Miklos


On 06/14/2010 03:11 PM, Henning Westerholt wrote:
> On Sunday 13 June 2010, Stefan Keller wrote:
>> I used the shm_regex functions from lib in one of my own modules and
>> noticed that it is dead-locking (it hangs in FUTEX_WAIT).
>> The code hangs in regexec() when trying to acquire the lock. This was
>> a bit hard to find out as I couldn't reproduce it in a virtual
>> machine with some test code I wrote. It turns out this only happens if
>> the machine has more than one physical CPU core.
>> Reproducable on x86_64 with two CPU cores, glibc 2.3.6 (from Debian
>> Etch) and glibc 2.11.1 (from Ubuntu Jaunty).
>> Attached is a patch which does its own locking and thus works around
>> this problem.
> 
> Hi Stefan,
> 
> thank you for the patch, it looks fine to me on a first sight. The library in 
> question is not used in any of the existing modules, so i think it should be 
> pretty save. Miklos, its ok when i apply it, or do you maybe want to refine it 
> a bit?
> 
> Regards,
> 
> Henning