Re: [boost] [interprocess][Shared memory]

From: Shibu Bera (shibu.ncst_at_[hidden])
Date: 2007-03-08 23:38:57

Hi,

Thanks Lon for the nice reply. I hope I will get a new method very soon.

I have one more query about the shared memory.

I create shared memory using boost::interprocess, at linking time I add

-lrt -lxml2 -lccext2 -lccgnu2 -ldl (common C++ link library) along with

-Wall -pedantic -g -pthread -DBOOST_DATE_TIME_NO_LIB
-DBOOST_INTERPROCESS_POSIX_PROCESS_SHARED -lstdc++ -lboost_thread
(boost::interprocess link library).

The common C++ library is added for the other requirement of the
application.

I open the shared memory form the another process, where "comman C++ link
library" is not added. Segmentation fault is the result.

Then I created two shared memory.
First with "common C++ link library" and "boost::interprocess link library"
And
Second with only "boost::interprocess link library",

These two shared memories are different, I found offset of some bytes on the
actual values stored in the shared memory. I am not finding the way, why
this problem is. I want to know how any other link libray may change the
data of the shared memory. Please help.

On 3/8/07, Ion Gaztañaga <igaztanaga_at_[hidden]> wrote:
>
> Shibu Bera wrote:
> > Hi,
> >
> > After creating the shared memory I put three containers
> (boost::multi_index,
> > std::map and std::vector) into the shared memory, then objects into the
> > containers. But in later part of the execution, there are condition when
> I
> > need to remove these elements and containers. I also don't want to eat
> up
> > the primary memory by creating the saparate shared memory nor I want to
> > remove the earlier shared memory. If I just destroy the containers the
> > previous garbage data may create problem. So I want such method or way
> to
> > memset the shared memory with NULL characters. This information should
> > suffice the query, Can I get some clue now?
>
> Which type of problems, security problems? Or do you base your program
> on the value the memory you allocate has before using it? If your
> destroy the containers and after that you create new ones, I think you
> shouldn't have problems. If for any reason, (security or whatever) you
> need to guarantee that all free memory (memory that does not contain any
> object in the segment) is zeroed before being reused, I would need to
> add new functionality to the library, because this is not currently
> possible: the memory allocation algorithm should have a function that
> traverses all the free memory segments and memsets them.
>
> These days I will be busy with the Intrusive review, so you would need
> to wait until the end of the month to get this functionality.
>
> Regards,
>
> Ion
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