浅析Werkzeug服务无缝更新「建议收藏」

    from werkzeug.serving import run_simple
    run_simple(...)

def run_with_reloader(main_func, extra_files=None, interval=1):
"""Run the given function in an independent python interpreter."""
# ********如果是真正需要运行的进程********
if os.environ.get('WERKZEUG_RUN_MAIN') == 'true':
    # ********启动服务线程********
    thread.start_new_thread(main_func, ())
    try:
        # ********检测文件变化并重启********
        reloader_loop(extra_files, interval)
    except KeyboardInterrupt:
        return
try:
    # ********第一次启动，按reloader方式启动子进程********
    sys.exit(restart_with_reloader())
except KeyboardInterrupt:
    pass


def restart_with_reloader():
    """Spawn a new Python interpreter with the same arguments as this one,
    but running the reloader thread.
    """
    while 1:
        _log('info', ' * Restarting with reloader...')
        args = [sys.executable] + sys.argv
        new_environ = os.environ.copy()

        # ********标记当前启动为真正要运行的进程********
        new_environ['WERKZEUG_RUN_MAIN'] = 'true'

        # a weird bug on windows. sometimes unicode strings end up in the
        # environment and subprocess.call does not like this, encode them
        # to latin1 and continue.
        if os.name == 'nt':
            for key, value in new_environ.iteritems():
                if isinstance(value, unicode):
                    new_environ[key] = value.encode('iso-8859-1')

        # ********创建新的子进程，执行参数和当前进程一致********
        # ********应该是直到子进程退出才会返回********
        exit_code = subprocess.call(args, env=new_environ)
        if exit_code != 3:
            return exit_code

     * Restarting with reloader...

realapp/
  |
  - __init__.py
dummy/
  |
  - __init__.py

    import sae, os

    if os.environ.get('WERKZEUG_RUN_MAIN') == 'true':
        print 'realy application'
        from realapp import app
        application = sae.create_wsgi_app(app)
    else:
        print 'dummy application'
        from dummy import dummy_app
        application = sae.create_wsgi_app(dummy_app)

os.environ.get('WERKZEUG_RUN_MAIN') != 'true'