The launchers have inheritance enabled (for the duplicated standard handles, which should be made inheritable via SetHandleInformation instead, but that's a separate issue). However, multiprocessing doesn't use inheritable handles. Spawning processes with inheritance would be a problem in a general-purpose library. Instead it depends on either the parent manually duplicating the handle to the child or vice versa (via the child opening the parent PID that's passed to it). The problem for a virtual environment that's using the launcher is the former, where the parent duplicates to the child (e.g. for the SemLock semaphore). We need a way to allow multiprocessing to spawn the real python.exe instead of the launcher executable that's set as sys.executable.