Re: [Boost-users] boost::interprocess container of pointers

Subject: Re: [Boost-users] boost::interprocess container of pointers
From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2009-11-22 13:47:58

Mateusz Ziobro escribió:
> Hi,
> I have a problem with container of pointers in shared memory using 
> boost::interprocess,
> object created by construct method is mapped to local memory address, so 
> I can not just put it into
> shared memory container because the address would be invalid in other 
> process,
> probably I have to remap or use some kind of smart pointer and than put 
> into container.
> My question is Does someone know how to do that? Please see following 
> piece of code.

If you store a offset_ptr in shared memory you can safely point to 
object constructed in that shared memory segment and that pointer will 
be dereferenced correctly in other processes. Another alternative is to 
use a handle_t integer to represent the shared address using

//!Transforms previously obtained offset into an absolute address in the
//!process space of the current process. Never throws.*/
void *    get_address_from_handle (handle_t offset) const

//!Transforms an absolute address into an offset from base address.
//!The address must belong to the memory segment. Never throws.
handle_t get_handle_from_address   (const void *ptr) const

http://www.boost.org/doc/libs/1_41_0/doc/html/interprocess/quick_guide.html#interprocess.quick_guide.qg_memory_pool

The most usual method is to construct offset_ptrs in shared memory 
pointing to the allocated object. But in your case, since your object is 
a named object ("test_data_set"), other processes can just use

managed_segment.find<TestDataSet>("test_data_set");

to obtain a valid address for its address space.

Best,

Ion