Re: [boost] [Review] Shmem

From: Jeff Flinn (TriumphSprint2000_at_[hidden])
Date: 2006-02-07 17:07:11

Ion Gaztañaga wrote:
> Hi fred,
>
>> First, there tends to be a create and object member function of a lot
>> of objects in the library. This forced Ion to create partially
>> constructed objects with the constructor, but it allows the use of
>> return values instead of exceptions for error handling. I personally
>> do not like partially constructed objects, and I do not mind
>> exceptions that are thrown if there's a serious problem detected. I'm
>> curious what the rationale was for that decision. Do the create/open
>> functions fail frequently in typical use cases?
>
> Can you elaborate a bit on this? I can't understand well what you are
> trying to point out.

I think he's pointing out the lack of RAII. From your first example:

  named_shared_object segment;

   if(!segment.create("/MySharedMemory",  //segment name
                     65536)){            //segment size in bytes
      return -1;
   }

   void * shptr   = segment.allocate(1024/*bytes to allocate*/);

   segment.deallocate(shptr);

I'd rather see:

  try
  {
     named_shared_object segment("/MySharedMemory",65536);

     shmem::shared_ptr lPtr = segment.allocate(1024);
  }
  catch( const shmem::exception& aExc )
  {
    ...
  }

Where the shared_ptr has a deleter calling named_shared_object::deallocate. 
I'd also think that the 'shared_memory' should not be destructed until the 
last shmem::shared_ptr is released.

Which brings up the issue that I could not easily find any discussion of 
lifetime requirements in the documentation.

Thanks, Jeff