How the PowerBuilder COM object executes
To establish an instance of a PowerBuilder COM object, the
PowerBuilder virtual machine (PBVM110.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 4MB 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 200K of memory; it shares the instance of the PowerBuilder
virtual machine and the cached memory.