Function spawn

src/debugpy/launcher/debuggee.py:40–175

(process_name, cmdline, env, redirect_output)

def spawn(process_name, cmdline, env, redirect_output):
    log.info(
        "Spawning debuggee process:\n\n"
        "Command line: {0!r}\n\n"
        "Environment variables: {1!r}\n\n",
        cmdline,
        env,
    )

    close_fds = set()
    try:
        if redirect_output:
            # subprocess.PIPE behavior can vary substantially depending on Python version
            # and platform; using our own pipes keeps it simple, predictable, and fast.
            stdout_r, stdout_w = os.pipe()
            stderr_r, stderr_w = os.pipe()
            close_fds |= {stdout_r, stdout_w, stderr_r, stderr_w}
            kwargs = dict(stdout=stdout_w, stderr=stderr_w)
        else:
            kwargs = {}

        if sys.platform != "win32" and sys.implementation.name != 'graalpy':
            # GraalPy does not support running code between fork and exec

            def preexec_fn():
                try:
                    # Start the debuggee in a new process group, so that the launcher can
                    # kill the entire process tree later.
                    os.setpgrp()

                    # Make the new process group the foreground group in its session, so
                    # that it can interact with the terminal. The debuggee will receive
                    # SIGTTOU when tcsetpgrp() is called, and must ignore it.
                    old_handler = signal.signal(signal.SIGTTOU, signal.SIG_IGN)
                    try:
                        tty = os.open("/dev/tty", os.O_RDWR)
                        try:
                            os.tcsetpgrp(tty, os.getpgrp())
                        finally:
                            os.close(tty)
                    finally:
                        signal.signal(signal.SIGTTOU, old_handler)
                except Exception:
                    # Not an error - /dev/tty doesn't work when there's no terminal.
                    log.swallow_exception(
                        "Failed to set up process group", level="info"
                    )

            kwargs.update(preexec_fn=preexec_fn)

        try:
            global process
            process = subprocess.Popen(cmdline, env=env, bufsize=0, **kwargs)
        except Exception as exc:
            raise messaging.MessageHandlingError(
                "Couldn't spawn debuggee: {0}\n\nCommand line:{1!r}".format(
                    exc, cmdline
                )