src/python/gem5/utils/multiprocessing/popen_spawn_gem5.py

# Copyright (c) 2022 The Regents of The University of California
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"""
This file contains extensions of the multiprocessing module to be used with gem5.
Specifically, it contains the code to spawn a new gem5 process with Popen.
Some code is from the Python standard library implementation of the
multiprocessing module (i.e., cpython/Lib/multiprocessing/).
"""

import io
import os

from multiprocessing.context import reduction, set_spawning_popen
from multiprocessing import popen_spawn_posix
from multiprocessing import spawn
from multiprocessing import util

from ._command_line import get_command_line

__all__ = ["Popen"]


class Popen(popen_spawn_posix.Popen):
    method = "spawn_gem5"

    def __init__(self, process_obj):
        super().__init__(process_obj)

    # Copyright (c) 2001-2022 Python Software Foundation; All Rights Reserved
    # from cpython/Lib/multiprocessing/popen_spawn_posix.py
    def _launch(self, process_obj):
        from multiprocessing import resource_tracker

        tracker_fd = resource_tracker.getfd()
        self._fds.append(tracker_fd)
        prep_data = spawn.get_preparation_data(process_obj._name)
        fp = io.BytesIO()
        set_spawning_popen(self)
        try:
            reduction.dump(prep_data, fp)
            reduction.dump(process_obj, fp)
        finally:
            set_spawning_popen(None)

        parent_r = child_w = child_r = parent_w = None
        try:
            parent_r, child_w = os.pipe()
            child_r, parent_w = os.pipe()
            # Note: This next line is the only modification
            cmd = get_command_line(
                tracker_fd=tracker_fd,
                pipe_handle=child_r,
                name=process_obj.name,
            )
            self._fds.extend([child_r, child_w])
            self.pid = util.spawnv_passfds(
                spawn.get_executable(), cmd, self._fds
            )
            self.sentinel = parent_r
            with open(parent_w, "wb", closefd=False) as f:
                f.write(fp.getbuffer())
        finally:
            fds_to_close = []
            for fd in (parent_r, parent_w):
                if fd is not None:
                    fds_to_close.append(fd)
            self.finalizer = util.Finalize(self, util.close_fds, fds_to_close)

            for fd in (child_r, child_w):
                if fd is not None:
                    os.close(fd)