Limitations on building Callin applications using the iris shared library (irisdb.dll)
When Callin applications are built using the shared library irisdb.dll, users who have large global buffer pools may see the Callin fail to initialize (in IrisStart) with an error:
<InterSystems IRIS Startup Error: Mapping shared memory (203)>
The explanation for this lies in the behavior of system DLLs loading in Windows. Applications coded in the Win 32 API or with the Microsoft Foundation Classes (the chief libraries that support Microsoft Visual C++ development) need to have the OS load the DLLs for that Windows code as soon as they initialize. These DLLs get loaded from the top of virtual storage (higher addresses), reducing the amount of space left for the heap. On most systems, there are also a number of other DLLs (for example, DLLs supporting the display graphics) that load automatically with each Windows process at locations well above the bottom of the virtual storage. These DLLs have a tendency to request a specific address space, most commonly 0X10000000 (256MB), chopping off a few hundred megabytes of contiguous memory at the bottom of virtual memory. The result may be that there is insufficient virtual memory space in the Callin executable in which to map the InterSystems IRIS shared memory segment.
