Function start_processes

torch/multiprocessing/spawn.py:205–238

(
    fn, args=(), nprocs=1, join=True, daemon=False, start_method="spawn"
)

# Currently we only add this API first, we can consider adding it to documentation as
# needed in the future.
def start_processes(
    fn, args=(), nprocs=1, join=True, daemon=False, start_method="spawn"
):
    mp = multiprocessing.get_context(start_method)
    error_files = []
    processes = []
    for i in range(nprocs):
        # Each process is assigned a file to write tracebacks to.  We
        # use the file being non-empty to indicate an exception
        # occurred (vs an expected shutdown).  Note: this previously
        # used a multiprocessing.Queue but that can be prone to
        # deadlocks, so we went with a simpler solution for a one-shot
        # message between processes.
        tf = tempfile.NamedTemporaryFile(
            prefix="pytorch-errorfile-", suffix=".pickle", delete=False
        )
        tf.close()
        os.unlink(tf.name)
        process = mp.Process(
            target=_wrap,
            args=(fn, i, args, tf.name),
            daemon=daemon,
        )
        process.start()
        error_files.append(tf.name)
        processes.append(process)

    context = ProcessContext(processes, error_files)
    if not join:
        return context

    # Loop on join until it returns True or raises an exception.
    while not context.join():
        pass


def spawn(fn, args=(), nprocs=1, join=True, daemon=False, start_method="spawn"):