import sys
from nova.cmd.api import main
if __name__ == "__main__":
　　sys.exit(main())

def main():
    config.parse_args(sys.argv)
    logging.setup("nova")
    utils.monkey_patch()

    launcher = service.process_launcher()
    for api in CONF.enabled_apis:
        should_use_ssl = api in CONF.enabled_ssl_apis
        if api == ‘ec2‘:
            """为了与ec2兼容"""
            server = service.WSGIService(api, use_ssl=should_use_ssl,
                                         max_url_len=16384) 
        else:
            server = service.WSGIService(api, use_ssl=should_use_ssl) 【1】
        launcher.launch_service(server, workers=server.workers or 1)【2】
    """当前进程处于等待状态"""
　　launcher.wait()

WSGIService类：
def __init__(self, name, loader=None, use_ssl=False, max_url_len=None):
    self.name = name
    self.manager = self._get_manager()
    self.loader = loader or wsgi.Loader()
    self.app = self.loader.load_app(name)
    self.host = getattr(CONF, ‘%s_listen‘ % name, "0.0.0.0")
    self.port = getattr(CONF, ‘%s_listen_port‘ % name, 0)
    self.workers = getattr(CONF, ‘%s_workers‘ % name, None)
    self.use_ssl = use_ssl
    """封装了wsgi.py中的server"""
    self.server = wsgi.Server(name,
                              self.app,
                              host=self.host,
                              port=self.port,
                              use_ssl=self.use_ssl,
                              max_url_len=max_url_len)
    # Pull back actual port used
    self.port = self.server.port
    self.backdoor_port = None

Loader类：
def __init__(self, config_path=None):
　　"""试图寻找api-paste.ini配置文件"""
　　self.config_path = None

　　config_path = config_path or CONF.api_paste_config
　　if not os.path.isabs(config_path):
　　　　self.config_path = CONF.find_file(config_path)
　　elif os.path.exists(config_path):
　　　　self.config_path = config_path

　　if not self.config_path:
　　　　raise exception.ConfigNotFound(path=config_path)

def load_app(self, name):
　　try:
　　　　LOG.debug("Loading app %(name)s from %(path)s",
                {‘name‘: name, ‘path‘: self.config_path})
　　　　return deploy.loadapp("config:%s" % self.config_path, name=name)
　　except LookupError as err:
　　　　LOG.error(err)
　　　　raise exception.PasteAppNotFound(name=name, path=self.config_path)    

ProcessLauncher类：
def launch_service(self, service, workers=1):
　　wrap = ServiceWrapper(service, workers)

　　LOG.info(_(‘Starting %d workers‘), wrap.workers)
　　"""循环启动workers数目的子进程"""
　　while self.running and len(wrap.children) < wrap.workers:
　　　　self._start_child(wrap)

def _start_child(self, wrap):
　　...
　　"""创建子进程"""
　　pid = os.fork()
　　if pid == 0:
            
　　　　status = 0
　　　　try:
　　　　　　"""子进程进行处理"""
　　　　　　self._child_process(wrap.service)
　　　　except SignalExit as exc:
　　　　　　signame = {signal.SIGTERM: ‘SIGTERM‘,
                    signal.SIGINT: ‘SIGINT‘}[exc.signo]
　　　　　　LOG.info(_(‘Caught %s, exiting‘), signame)
　　　　　　status = exc.code
　　　　except SystemExit as exc:
　　　　　　status = exc.code
　　　　except BaseException:
　　　　　　LOG.exception(_(‘Unhandled exception‘))
　　　　　　status = 2
　　　　finally:
　　　　　　"""出现异常停掉服务"""
　　　　　　wrap.service.stop()
　　　　"""子进程退出"""
　　　　os._exit(status)

　　LOG.info(_(‘Started child %d‘), pid)
　　wrap.children.add(pid)
　　self.children[pid] = wrap
　　return pid



def _child_process(self, service):
　　...
　　launcher = Launcher()
　　launcher.run_service(service)

Launcher类：
def __init__(self):
    self._services = threadgroup.ThreadGroup()
    self.backdoor_port = eventlet_backdoor.initialize_if_enabled() 


@staticmethod
def run_service(service):
    service.start()
    service.wait()

WSGIService类：
def start(self):
if self.manager:
        self.manager.init_host()
        self.manager.pre_start_hook()
        if self.backdoor_port is not None:
            self.manager.backdoor_port = self.backdoor_port
    self.server.start()
    if self.manager:
        self.manager.post_start_hook()


def wait(self):
    self.server.wait()

Server类：
def start(self):
    ...
    wsgi_kwargs = {
        ‘func‘: eventlet.wsgi.server,
        ‘sock‘: self._socket,
        ‘site‘: self.app,
        ‘protocol‘: self._protocol,
        ‘custom_pool‘: self._pool,
        ‘log‘: self._wsgi_logger,
        ‘log_format‘: CONF.wsgi_log_format
        }

    if self._max_url_len:
        wsgi_kwargs[‘url_length_limit‘] = self._max_url_len
    """创建一个green thread，运行func函数，在其中传入后面的参数。此处为调用eventlet.wsgi.server函数，传入sock=self._socket等参数到server函数中。其中eventlet.wsgi.server函数负责启动一个wsgi服务器程序接受客户端发来的请求，
可以参考：http://eventlet.net/doc/modules/wsgi.html?highlight=wsgi.server#eventlet.wsgi.server"""
    self._server = eventlet.spawn(**wsgi_kwargs)


def wait(self):
    try:
        """green thread阻塞等待"""
        self._server.wait()
    except greenlet.GreenletExit:
        LOG.info(_("WSGI server has stopped."))