[boost] [shmem] Contribution

From: Michael Pryhodko (crusader.mike_at_[hidden])
Date: 2006-03-01 06:21:50

Hi

I am not active 'Boost' participant, but I keep an eye on this project and 
check it's status from time to time. During last couple of years I was 
involved in IPC and was naturally intrigued by the new boost library --  
Shared Memory Library. In documentation I have read that:

[------- start -------]
 To place STL-compatible containers in shared memory, Shmem allocators 
define allocator<T>::pointer typedef as a relative pointer type, instead of 
T*. Although the use of smart pointers is allowed by the standard, current 
STL implementations can't handle Shmem shared memory STL compatible 
allocators.
[------- end -------]

But in my recent project I actually created allocator for shared memory that 
can be used in STL from MS VC7.1. Rejected two or three version of 
allocator::pointer until it worked.  And I used it successfully: in my 
project complex structures with maps, deques, vectors, pointers and even 
smart pointers were created in shared memory. Only problem I have found --  
std::basic_string, it explicitly uses T* in union. I have used 
limited_string or vector<char> instead of it.

If anybody interested -- just ask for more details, until then I'll 
demonstrate simple example and allocator declaration:

[------- start example -------]
template<class MemModel = StdMemModel>
class RootObject : public MemModel::ObjectBase
{
public:
    typedef ProcessContext<MemModel> ProcessContext;
    typedef typename MemModel::rebind<ProcessContext>::Allocator::pointer 
ProcessContextPtr;

//...

private:
    // process context map<ProcId, ProcessContextPtr>
    typedef std::map<DWORD, ProcessContextPtr, std::less<DWORD>,
        typename MemModel::rebind<std::pair<DWORD const, ProcessContextPtr> 
 >::Allocator>
            ProcessMap;

    ProcessMap m_procMap;
};

// later in the code:
if (useShared)
{
    new RootObject <SharedModel>();
}
else
{
    new RootObject <>();
}

[------- end example -------]

I'll try to attach shared allocator declaration, hope that this newsgroup 
allows this.

Bye.
Sincerely yours, Michael.

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