django_autoreload.py

# Autoreloading launcher.
# Borrowed from Peter Hunt and the CherryPy project (https://cherrypy.org/).
# Some taken from Ian Bicking's Paste (http://pythonpaste.org/).
#
# Portions copyright (c) 2004, CherryPy Team (team@cherrypy.org)
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without modification,
# are permitted provided that the following conditions are met:
#
#     * Redistributions of source code must retain the above copyright notice,
#       this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above copyright notice,
#       this list of conditions and the following disclaimer in the documentation
#       and/or other materials provided with the distribution.
#     * Neither the name of the CherryPy Team nor the names of its contributors
#       may be used to endorse or promote products derived from this software
#       without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

import os
import signal
import subprocess
import sys
import time
import traceback

import _thread

from django.apps import apps
from django.conf import settings
from django.core.signals import request_finished

# This import does nothing, but it's necessary to avoid some race conditions
# in the threading module. See https://code.djangoproject.com/ticket/2330 .
try:
    import threading  # NOQA
except ImportError:
    pass

try:
    import termios
except ImportError:
    termios = None

USE_INOTIFY = False
try:
    # Test whether inotify is enabled and likely to work
    import pyinotify

    fd = pyinotify.INotifyWrapper.create().inotify_init()
    if fd >= 0:
        USE_INOTIFY = True
        os.close(fd)
except ImportError:
    pass

RUN_RELOADER = True

FILE_MODIFIED = 1
I18N_MODIFIED = 2

_mtimes = {}
_win = (sys.platform == "win32")

_exception = None
_error_files = []
_cached_modules = set()
_cached_filenames = []


def gen_filenames(only_new=False):
    """
    Return a list of filenames referenced in sys.modules and translation files.
    """
    # N.B. ``list(...)`` is needed, because this runs in parallel with
    # application code which might be mutating ``sys.modules``, and this will
    # fail with RuntimeError: cannot mutate dictionary while iterating
    global _cached_modules, _cached_filenames
    module_values = set(sys.modules.values())
    _cached_filenames = clean_files(_cached_filenames)
    if _cached_modules == module_values:
        # No changes in module list, short-circuit the function
        if only_new:
            return []
        else:
            return _cached_filenames + clean_files(_error_files)

    new_modules = module_values - _cached_modules
    new_filenames = clean_files(
        [filename.__file__ for filename in new_modules
         if hasattr(filename, '__file__')])

    if not _cached_filenames and settings.USE_I18N:
        # Add the names of the .mo files that can be generated
        # by compilemessages management command to the list of files watched.
        basedirs = [os.path.join(os.path.dirname(os.path.dirname(__file__)),
                                 'conf', 'locale'),
                    'locale']
        for app_config in reversed(list(apps.get_app_configs())):
            basedirs.append(os.path.join(app_config.path, 'locale'))
        basedirs.extend(settings.LOCALE_PATHS)
        basedirs = [os.path.abspath(basedir) for basedir in basedirs
                    if os.path.isdir(basedir)]
        for basedir in basedirs:
            for dirpath, dirnames, locale_filenames in os.walk(basedir):
                for filename in locale_filenames:
                    if filename.endswith('.mo'):
                        new_filenames.append(os.path.join(dirpath, filename))

    _cached_modules = _cached_modules.union(new_modules)
    _cached_filenames += new_filenames
    if only_new:
        return new_filenames + clean_files(_error_files)
    else:
        return _cached_filenames + clean_files(_error_files)


def clean_files(filelist):
    filenames = []
    for filename in filelist:
        if not filename:
            continue
        if filename.endswith(".pyc") or filename.endswith(".pyo"):
            filename = filename[:-1]
        if filename.endswith("$py.class"):
            filename = filename[:-9] + ".py"
        if os.path.exists(filename):
            filenames.append(filename)
    return filenames


def reset_translations():
    import gettext
    from django.utils.translation import trans_real
    gettext._translations = {}
    trans_real._translations = {}
    trans_real._default = None
    trans_real._active = threading.local()


def inotify_code_changed():
    """
    Check for changed code using inotify. After being called
    it blocks until a change event has been fired.
    """
    class EventHandler(pyinotify.ProcessEvent):
        modified_code = None

        def process_default(self, event):
            if event.path.endswith('.mo'):
                EventHandler.modified_code = I18N_MODIFIED
            else:
                EventHandler.modified_code = FILE_MODIFIED

    wm = pyinotify.WatchManager()
    notifier = pyinotify.Notifier(wm, EventHandler())

    def update_watch(sender=None, **kwargs):
        if sender and getattr(sender, 'handles_files', False):
            # No need to update watches when request serves files.
            # (sender is supposed to be a django.core.handlers.BaseHandler subclass)
            return
        mask = (
            pyinotify.IN_MODIFY |
            pyinotify.IN_DELETE |
            pyinotify.IN_ATTRIB |
            pyinotify.IN_MOVED_FROM |
            pyinotify.IN_MOVED_TO |
            pyinotify.IN_CREATE |
            pyinotify.IN_DELETE_SELF |
            pyinotify.IN_MOVE_SELF
        )
        for path in gen_filenames(only_new=True):
            wm.add_watch(path, mask)

    # New modules may get imported when a request is processed.
    request_finished.connect(update_watch)

    # Block until an event happens.
    update_watch()
    notifier.check_events(timeout=None)
    notifier.read_events()
    notifier.process_events()
    notifier.stop()

    # If we are here the code must have changed.
    return EventHandler.modified_code


def code_changed():
    global _mtimes, _win
    for filename in gen_filenames():
        stat = os.stat(filename)
        mtime = stat.st_mtime
        if _win:
            mtime -= stat.st_ctime
        if filename not in _mtimes:
            _mtimes[filename] = mtime
            continue
        if mtime != _mtimes[filename]:
            _mtimes = {}
            try:
                del _error_files[_error_files.index(filename)]
            except ValueError:
                pass
            return I18N_MODIFIED if filename.endswith('.mo') else FILE_MODIFIED
    return False


def check_errors(fn):
    def wrapper(*args, **kwargs):
        global _exception
        try:
            fn(*args, **kwargs)
        except Exception:
            _exception = sys.exc_info()

            et, ev, tb = _exception

            if getattr(ev, 'filename', None) is None:
                # get the filename from the last item in the stack
                filename = traceback.extract_tb(tb)[-1][0]
            else:
                filename = ev.filename

            if filename not in _error_files:
                _error_files.append(filename)

            raise

    return wrapper


def raise_last_exception():
    global _exception
    if _exception is not None:
        raise _exception[1]


def ensure_echo_on():
    if termios:
        fd = sys.stdin
        if fd.isatty():
            attr_list = termios.tcgetattr(fd)
            if not attr_list[3] & termios.ECHO:
                attr_list[3] |= termios.ECHO
                if hasattr(signal, 'SIGTTOU'):
                    old_handler = signal.signal(signal.SIGTTOU, signal.SIG_IGN)
                else:
                    old_handler = None
                termios.tcsetattr(fd, termios.TCSANOW, attr_list)
                if old_handler is not None:
                    signal.signal(signal.SIGTTOU, old_handler)


def reloader_thread():
    ensure_echo_on()
    if USE_INOTIFY:
        fn = inotify_code_changed
    else:
        fn = code_changed
    while RUN_RELOADER:
        change = fn()
        if change == FILE_MODIFIED:
            sys.exit(3)  # force reload
        elif change == I18N_MODIFIED:
            reset_translations()
        time.sleep(1)


def restart_with_reloader():
    import django.__main__
    while True:
        args = [sys.executable] + ['-W%s' % o for o in sys.warnoptions]
        if sys.argv[0] == django.__main__.__file__:
            # The server was started with `python -m django runserver`.
            args += ['-m', 'django']
            args += sys.argv[1:]
        else:
            args += sys.argv
        new_environ = {**os.environ, 'RUN_MAIN': 'true'}
        exit_code = subprocess.call(args, env=new_environ)
        if exit_code != 3:
            return exit_code


def python_reloader(main_func, args, kwargs):
    if os.environ.get("RUN_MAIN") == "true":
        _thread.start_new_thread(main_func, args, kwargs)
        try:
            reloader_thread()
        except KeyboardInterrupt:
            pass
    else:
        try:
            exit_code = restart_with_reloader()
            if exit_code < 0:
                os.kill(os.getpid(), -exit_code)
            else:
                sys.exit(exit_code)
        except KeyboardInterrupt:
            pass


def main(main_func, args=None, kwargs=None):
    if args is None:
        args = ()
    if kwargs is None:
        kwargs = {}

    wrapped_main_func = check_errors(main_func)
    python_reloader(wrapped_main_func, args, kwargs)

principle:

• parent: create a new child process and run it with the same command line arguments, wait for child process to finish, collect the exit code, if exit code equals 3, then rerun it, else exit.
• child: create a new thread to run the real program logic, meanwhile the main thread polls for source file changes, if any change happens, exit with code = 3.