def patch_multiprocessing(rcfile: str) -> None:
    """Monkey-patch the multiprocessing module.

    This enables coverage measurement of processes started by multiprocessing.
    This involves aggressive monkey-patching.

    `rcfile` is the path to the rcfile being used.

    """

    if hasattr(multiprocessing, PATCHED_MARKER):
        return

    OriginalProcess._bootstrap = ProcessWithCoverage._bootstrap     # type: ignore[attr-defined]

    # Set the value in ProcessWithCoverage that will be pickled into the child
    # process.
    os.environ["COVERAGE_RCFILE"] = os.path.abspath(rcfile)

    # When spawning processes rather than forking them, we have no state in the
    # new process.  We sneak in there with a Stowaway: we stuff one of our own
    # objects into the data that gets pickled and sent to the subprocess. When
    # the Stowaway is unpickled, its __setstate__ method is called, which
    # re-applies the monkey-patch.
    # Windows only spawns, so this is needed to keep Windows working.
    try:
        from multiprocessing import spawn
        original_get_preparation_data = spawn.get_preparation_data
    except (ImportError, AttributeError):
        pass
    else:
        def get_preparation_data_with_stowaway(name: str) -> dict[str, Any]:
            """Get the original preparation data, and also insert our stowaway."""
            d = original_get_preparation_data(name)
            d["stowaway"] = Stowaway(rcfile)
            return d

        spawn.get_preparation_data = get_preparation_data_with_stowaway

    setattr(multiprocessing, PATCHED_MARKER, True)
Monkey-patch the multiprocessing module.

    This enables coverage measurement of processes started by multiprocessing.
    This involves aggressive monkey-patching.

    `rcfile` is the path to the rcfile being used.

    
coverage/multiproc.py