How the PowerBuilder COM object executes – PB Docs 70

How the PowerBuilder COM object executes

To establish an instance of a PowerBuilder COM object, the PowerBuilder virtual
machine (PBVM70.DLL) loads the custom class object from
the PBD embedded in the COM server DLL and creates the proper session
and instance information. When a client invokes a PowerBuilder COM
object method, the method calls back into the PowerBuilder virtual
machine to execute the appropriate PowerScript code.

PowerBuilder COM servers use the COM single-threaded apartment
(STA) model. Runtime sessions can be shared by objects created on
the same thread. When a client requests an instance of a PowerBuilder COM
object, the PowerBuilder COM server establishes a runtime session
and creates an instance of the custom class user object within that
runtime session. When the server receives a new request for an instance
of a COM object from the same thread, it instantiates the object
using the existing runtime session.

In all cases, separate clients use distinct PowerBuilder virtual
machine sessions.

Memory allocation

The first time any client requests an instance of a PowerBuilder COM
object from a PowerBuilder COM server, the server loads the PowerBuilder virtual machine,
allocates a block of memory, and starts a runtime session. About
4 MB of memory is allocated for the PowerBuilder virtual machine,
cached memory, and the runtime session.

Subsequent requests do not require any additional memory allocation
if the objects can share the same runtime session.

If a subsequent request requires a PowerBuilder COM object to
be created in a different COM apartment (usually because the request
was made from a different client or thread), the object is instantiated
in a new runtime session. Each new session requires only about 200
KB of memory; it shares the instance of the PowerBuilder virtual machine
and the cached memory.

Document get from Powerbuilder help
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