[boost] [interprocess] atomic_write32 on GCC/x86/x68_64 lacks memory barrier

Subject: [boost] [interprocess] atomic_write32 on GCC/x86/x68_64 lacks memory barrier
From: Lars Hagström (lars_at_[hidden])
Date: 2014-08-08 08:28:44

Hi!

In a piece of legacy code I've had a few uses of the atomic operations
inside Boost.Interprocess (yes, I know they're internal, but I had no other
choice at the time, so sue me :-).
I've been debugging a thread synchronization issue which ended up in me
actually looking for a problem inside interprocess, and I believe that I
found the error.
The atomic_write32 function, when running gcc on intel platforms does not
have a memory barrier, which causes my threads to not see changes that they
should see.

A little bit of googling gave me the following link
http://boost.2283326.n4.nabble.com/interprocess-atomic-write32-td4173289.html,
which discusses exactly this issue.

I've now fixed my code to use Boost.Atomic instead of relying on boost
interprocess internals, so I'm good, but I worry that the issue might
affect boost.interprocess as well.

So I propose that atomic_write32 should be implemented using atomic_cas32.
Or indeed that Boost.Atomic should be used instead, which is more work,
obviously.

Thoughts?

/Lars