When Houdini/hython is started, it uses all available processors on
the machine for multi-threaded processing, unless overridden by the
-j command line option.
This function allows dynamically adjusting this setting at run-time.
Note that this function may only be called from the main thread. If called from an expression that gets evaluated in a multi-threaded context, or during other processing, it will throw an exception.
The effectiveness of this function differs on different platforms. Prefer
-j command line option setting the
environment variable instead.
This function currently has no effect on Linux if there are OpenCL nodes present in the scene.