Hello dear boost users, I am trying to use the shmem library for the first time. The domain of the application is centered on the passing of image frames from process that acquires the images to the client process via a local shared memory segment. In short, nothing really complicated. A synchronized writer/reader process. I started from looking at processA/processB example in the example directory. I am using boost 1.33.1 and shmem 0.93 (the latest available from boost vault). If I open the segment with the exact number of bytes needed:
const int memsize = 320*240; //Create shared memory if(!segment.open_or_create(shMemName, memsize)){ std::cout << "error creating shared memory\n"; return -1; };
Then I cannot use:
unsigned char* uchar_ptr = (unsigned char*)segment.allocate(num_elements);
with num_elements equal to the memsize. I see that there is need for an extra memory space to pass as second argument to the open() function... (for example 320*240+1024) ... How can I know in advance how many bytes are necessary to allocate the space actually needed? For instance, what is the difference between the size in open(..) and allocate(..)? In this case I just need a raw_memory segment .... In more complex cases? Is there some rule of thumb? Andrea Carbone