Re: [boost] [Interprocess] Loosing shared memory when exiting scope

Subject: Re: [boost] [Interprocess] Loosing shared memory when exiting scope
From: Dominique Devienne (ddevienne_at_[hidden])
Date: 2011-02-22 10:09:53

On Tue, Feb 22, 2011 at 5:22 AM, supplier <supplier_at_[hidden]> wrote:
>  3   >    // Connecting to the existing shared memory
>  4   >    SharedMemoryRiiConnector shmem("Some Name");

FYI: Such RAII wrappers are often called ScopedXyz, like
boost::scoped_ptr for example.

>  6   >    // Do some stuff here, for example calling a function creating objects
>  7   >    TypeR* instance = createObjectInSharedMemory();
>  8   >
>  9   >    // Call a member function of TypeR
> 10   >    instance->doSomething();
> 11   >    [...]
> 12   >  }
> 13   >
> 14   > TypeR* classB::createObjectInSharedMemory()
> 15   > {
> 16   >    // Connect to the shared memory again to allow working in this
> 17   >    SharedMemoryRiiConnector shmem("Some Name");
> 18   >
> 19   >    // Create an object in the shared memory using the interface of the
> 20   >    // RII object, which uses the Boost.Interprocess functions to handle allocation
> 21   >    TypeR* instance = shmem.createObject<TypeR>("Example Object");
> 22   >    return instance;
> 23   > }

The app I work on uses SHM and on Windows I noticed that when you
attach several time to the same SHM segment in different parts of the
same process, you don't necessarily get back the same pointer. We
don't use Boost for the SHM handling and I don't know what's in your
SharedMemoryRiiConnector, so we may be in a different situation, but
if SharedMemoryRiiConnector re-opens the SHM, the address you get on
line 17 might be different than the address you get on line 4, and the
first address is only valid in the scope of
classB::createObjectInSharedMemory, since the RAII wrapper likely
closes its SHM segment on line 23. It's only a guess, but as it fits
your symptoms I'm throwing it out there. Good luck, --DD