Re: [boost] [interprocess] problem in boost/interprocess/detail/atomic.hpp

From: Glenn Schrader (gschrad_at_[hidden])
Date: 2006-12-16 14:10:07

Hello Ion,
Ion Gaztañaga wrote:
> Hi Glenn,
>
> Glenn Schrader wrote:
>   
>> I ran across this bug while running on a 2.6.9 Linux kernel. Since that 
>> kernel version doesn't have native interprocess mutexes and condition 
>> variables the interprocess library uses some emulation code. The x86 
>> verion of the emulated semaphore uses atomic_dec32() from atomic.hpp but 
>> that function wasn't behaving properly. The following change in 
>> oost/interprocess/detail/atomic.hpp made things work properly:
>>     
>
> Thanks for the change. However, I'm pretty sure that Linux has 
> process-shared mutexes and condition variables. This might be a bug from 
> the last version. Can you check against the CVS code?
>   
Since interprocess isn't in the official tarball yet i've been working 
with the head version from CVS. Whether or not emulation is used is 
determined by the value in _POSIX_THREAD_PROCESS_SHARED. In a 2.6.17 
kernel that I'm running on another system the value is 200112L so indeed 
the native mutexes and condition variables are used. The system that I 
was having a problem with has a 2.6.9 kernel and the 
_POSIX_THREAD_PROCESS_SHARED value of -1; corresponding to "not supported".
> I will apply your patch ASAP to CVS. This really shows that atomic 
> functions in hands of non expert people like me are really dangerous! 
> Let's hope we can see soon an atomic operations library in Boost.
>   
No problem and and thanks!

-glenn