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Passing block of memory safely between classes

 
 
tech
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Posts: n/a
 
      04-18-2008
Hi, I need to pass a block of say 320 bytes memory between some
classes
which do various processing on it. The app needs to be quick so i
can't
keep copying.

The simplest way is via pointer say:

class A
{

void Transmitdata(const short* data, size_t Insize, char* output,
size_t OutSize)
{
// do some processing on data

}

};

alternative which seems to be a lot safer is
void Transmitdata(const std::vector<short>& buf, std::vector<char>&
outBuf)
{

}
The vectors know there size so each class doesn't need to worry about
the size
of data the pointers are pointing to


Its just that the block of memory i want to pass around is in some
shared memory
area and i can't overlay a vector onto a block of memory as it makes a
copy so at present
i'm just stuck with the pointers. Anyone know a way round this?


 
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SeanW
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      04-18-2008
On Apr 18, 10:19 am, tech <(E-Mail Removed)> wrote:
> Hi, I need to pass a block of say 320 bytes memory between some
> classes
> which do various processing on it. The app needs to be quick so i
> can't
> keep copying.
>
> The simplest way is via pointer say:
>
> class A
> {
>
> void Transmitdata(const short* data, size_t Insize, char* output,
> size_t OutSize)
> {
> // do some processing on data
>
> }
> };
>
> alternative which seems to be a lot safer is
> void Transmitdata(const std::vector<short>& buf, std::vector<char>&
> outBuf)
> {
>
> }
>
> The vectors know there size so each class doesn't need to worry about
> the size
> of data the pointers are pointing to
>
> Its just that the block of memory i want to pass around is in some
> shared memory
> area and i can't overlay a vector onto a block of memory as it makes a
> copy so at present
> i'm just stuck with the pointers. Anyone know a way round this?


You might be interested in this project, "A C++ Pooled,
Shared Memory Allocator For The Standard Template Library":

http://allocator.sourceforge.net/

As always with C++, it's not as easy as you'd like (for
one compiler, at least):

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21251

You might also find this page on writing your own
allocator interesting:

http://www.codeproject.com/KB/cpp/allocator.aspx

Sean

 
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Puppet_Sock
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Posts: n/a
 
      04-18-2008
On Apr 18, 10:19*am, tech <(E-Mail Removed)> wrote:
> Hi, I need to pass a block of say 320 bytes memory between some
> classes
> which do various processing on it. The app needs to be quick so i
> can't
> keep copying.
>
> The simplest way is via pointer say:
>
> class A
> {
>
> void Transmitdata(const short* *data, size_t Insize, char* output,
> size_t OutSize)
> {
> * *// do some processing on data
>
> }
> };
>
> alternative which seems to be a lot safer is
> void Transmitdata(const std::vector<short>& buf, std::vector<char>&
> outBuf)
> {
>
> }
>
> The vectors know there size so each class doesn't need to worry about
> the size
> of data the pointers are pointing to
>
> Its just that the block of memory i want to pass around is in some
> shared memory
> area and i can't overlay a vector onto a block of memory as it makes a
> copy so at present
> i'm just stuck with the pointers. Anyone know a way round this?


That's easy. You want to pass a reference to an instance
of a class that can safely encapsulate a shared memory block.

But you don't have a class that can safely encapsulate
your shared memory block.

So you write a class that can safely encapsulate your
shared memory block.

Lots of ways to do that, depending on the specifics of the
memory block. If it is a bunch of integers, as your example
suggests, it's way easy. For example, you can just have
a pointer in the class and initialize an instance to point
to the memory block. And have it carry around the size
info for the block as well. After that it depends on how
much you want to pack into the class, and how much you
want to have as routines outside the class. Chances are
good you will want to look at a singleton pattern as well.
Then pretty much all your tasks on the memory block are
going to be member functions of the class.
Socks
 
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kasthurirangan.balaji@gmail.com
Guest
Posts: n/a
 
      04-19-2008
On Apr 18, 9:19 am, tech <(E-Mail Removed)> wrote:
> Hi, I need to pass a block of say 320 bytes memory between some
> classes
> which do various processing on it. The app needs to be quick so i
> can't
> keep copying.
>
> The simplest way is via pointer say:
>
> class A
> {
>
> void Transmitdata(const short* data, size_t Insize, char* output,
> size_t OutSize)
> {
> // do some processing on data
>
> }
> };
>
> alternative which seems to be a lot safer is
> void Transmitdata(const std::vector<short>& buf, std::vector<char>&
> outBuf)
> {
>
> }
>
> The vectors know there size so each class doesn't need to worry about
> the size
> of data the pointers are pointing to
>
> Its just that the block of memory i want to pass around is in some
> shared memory
> area and i can't overlay a vector onto a block of memory as it makes a
> copy so at present
> i'm just stuck with the pointers. Anyone know a way round this?


you may want to look at boost interprocess(www.boost.org).

Thanks,
Balaji.
 
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