The man page for top defines SHR as:
t: SHR -- Shared Mem size (kb) The amount of shared memory used by a task. It simply reflects memory that could be potentially shared with other processes.
I can see this growing for one process but I am unsure of what exactly is being reported here. The shared object library linked by this process is allocating and deallocating memory but not opening any shared memory segments, and pmap is not showing any other libraries being loaded. What else makes up the shared memory size, and how else can I get information about it?