Call of the cocos2d-x CCNode isRunning Function

For example, if the bullet exceeded the screen, we will remove the bullet from the removeChild layer. So, is there a status to determine whether the bullet has been removed? It is determined by the isRunning function. If the bullet is still in the layer, isRunning returns true. If layer-> removeChild is called, isRunning returns false; when is the status of the isRunning function set? When CCLayer-> addChild is called, CCNode is called. onEnter sets isRunning here. When CCLayer-> removeChild is called, CCNode is called. onExit will clear isRunning again here; this is a very good sign for judgment.