我們來看看節(jié)點管理器master是如何被啟動的，再回到parent.pystart()函數(shù)，如下。

我們發(fā)現(xiàn)它啟動了XMLRPC服務(wù)器后，接下來就調(diào)用了_init_runner()函數(shù)。

def start(self, auto_terminate=True):
        self.logger.info("starting roslaunch parent run")
        # load config, start XMLRPC servers and process monitor
        try:
            self._start_infrastructure()
        except:
            self._stop_infrastructure()
        # Initialize the actual runner. 
        self._init_runner()
        # Start the launch
        self.runner.launch()

init_runner()函數(shù)實例化了ROSLaunchRunner類，這個類的定義在launch.py里。

def _init_runner(self):
         self.runner = roslaunch.launch.ROSLaunchRunner(self.run_id, self.config, server_uri=self.server.uri, ...)

實例化完成后，parent.pystart()函數(shù)就調(diào)用了它的launch()函數(shù)。

我們打開launch.py文件，找到launch()函數(shù)，發(fā)現(xiàn)它又調(diào)用了自己類中的_setup()函數(shù)，而_setup()函數(shù)又調(diào)用了_launch_master()函數(shù)。

看名字就能猜出來，_launch_master()函數(shù)肯定是啟動節(jié)點管理器master的，它調(diào)用了create_master_process函數(shù)，這個函數(shù)在nodeprocess.py里。

所以我們打開nodeprocess.py，create_master_process函數(shù)使用了LocalProcess類。這個類繼承自Process類。nodeprocess.py文件引用了python中用于創(chuàng)建新的進(jìn)程的subprocess模塊。

create_master_process函數(shù)實例化LocalProcess類用的是’rosmaster’，即ros_comm-noetic-develtoolsrosmaster中的包。

main.py文件中的rosmaster_main函數(shù)使用了master.py中的Master類。

Master類中又用到了master_api.py中的ROSMasterHandler類，這個類包含所有的XMLRPC服務(wù)器接收的遠(yuǎn)程調(diào)用，一共24個，如下。

shutdown(self, caller_id, msg='')
getUri(self, caller_id)
getPid(self, caller_id)
deleteParam(self, caller_id, key)
setParam(self, caller_id, key, value)
getParam(self, caller_id, key)
searchParam(self, caller_id, key)
subscribeParam(self, caller_id, caller_api, key)
unsubscribeParam(self, caller_id, caller_api, key)
hasParam(self, caller_id, key)
getParamNames(self, caller_id)
param_update_task(self, caller_id, caller_api, param_key, param_value)
_notify_topic_subscribers(self, topic, pub_uris, sub_uris)
registerService(self, caller_id, service, service_api, caller_api)
lookupService(self, caller_id, service)
unregisterService(self, caller_id, service, service_api)
registerSubscriber(self, caller_id, topic, topic_type, caller_api)
unregisterSubscriber(self, caller_id, topic, caller_api)
registerPublisher(self, caller_id, topic, topic_type, caller_api)
unregisterPublisher(self, caller_id, topic, caller_api)
lookupNode(self, caller_id, node_name)
getPublishedTopics(self, caller_id, subgraph)
getTopicTypes(self, caller_id) 
getSystemState(self, caller_id)