Hi Fred,
After rereading the documentation and reading the code, I think I was confused when I wrote this. It appears that the shared_message_queue cannot be used for objects created with the named_shared_object::construct member function. A memcpy is done on the buffer passed into send, so objects cannot be sent. Thus, a void* is correct.
I do think that the documentation should be improved on that. I wasn't sure until I dug into the source code. If there are other places in the shmem library that don't support objects, I'd like to see those documented as well.
Surely documentation can be improved to show that shared_message_queue is a common, byte copying message queue between processes, just like localhost UDP socket messaging. The meaning of the bytes should be common between applications, the queue just forwards byte packets. The queue is an example of a higher level IPC mechanism built using Shmem primitives (shared memory, shared memory conditions and mutexes). You can pass structured data using shared message queue, just like the example of the section shows. You can build all your objects in a user buffer and byte-serialize it through the message queue. This is different from building it in shared memory, but like using shared memory, both processes must be ABI-compatible.
Shmem is the first library I've seen that tries to support passing a C++ object through shared memory to another process. It seems like a really good idea, and I'd be happier if it were supported throughout the library. Maybe the shared_message_queue should support only offset_ptr's to objects that are created elsewhere in the named_shared_object?
I think that a message queue like this should not care about the contained bytes. If you need a queue of objects of the same type. It's clear that you can build a STL-like object queue above shared_message_queue doing your casts. If that is a need, I'm ready to implement a "shared_object_queue". But these passed objects must be self-contained, I mean, you can pass a boost::shmem::vector<> because I would need to know how to bye-serialize it. However, you can use named_heap_object, construct in a single buffer all your complex data, and byte-copy it to another process to pass all the information. Regards, Ion