Webots多E-puck机器人项目报错：仅允许创建一个Robot类实例

问题背景 #

开发Webots项目时，使用四个E-puck机器人推送箱子至目标位置，代码采用Environment类、Robot类加主控制循环的结构。运行时出现错误：Only one instance of the Robot class should be created，同时收到警告：'Supervisor' controller exited with status: -1。相关代码片段如下：

_robot_instance = None
_supervisor_instance = None
def __init__(self, use_supervisor=False):
    self.use_supervisor = use_supervisor
    self.TIME_STEP = 32
    self.receiver = None
    self.webots_supervisor = None
    if use_supervisor:
        if Environment._supervisor_instance is None:
            Environment._supervisor_instance = Supervisor()
        self.webots_supervisor = Environment._supervisor_instance
        self.robot = self.webots_supervisor.getFromDef("agent1")
    else:
        if Environment._robot_instance is None:
            Environment._robot_instance = Robot()
        self.robot = Environment._robot_instance
def reset(self):
    print(f"Supervisor: {self.webots_supervisor}")
    # Release existing Robot/Supervisor instance if it exists
    if self.use_supervisor:
        if Environment._supervisor_instance is not None:
            self.webots_supervisor = None
            self.robot = None
            del Environment._supervisor_instance
    else:
        if Environment._robot_instance is not None:
            self.robot = None
    # Create a new Robot/Supervisor instance
    if use_supervisor:
        Environment._supervisor_instance = Supervisor()
        self.webots_supervisor = Environment._supervisor_instance
        self.robot = self.webots_supervisor.getFromDef("agent1")
    else:
        if Environment._robot_instance is None:
            Environment._robot_instance = Robot()
        self.robot = Environment._robot_instance
    try:
        # Ensure that Supervisor instance is used when appropriate
        root = (
            self.webots_supervisor.getRoot()
            if self.use_supervisor
            else self. robot.getRoot()
        )
        self.print_node_names(root)
    except AttributeError as e:
        print(f"Error getting nodes: {e}")

错误原因分析 #

1. Robot实例重复创建：reset方法的非Supervisor分支中，删除旧实例后未置空类变量_robot_instance，导致下次创建时if Environment._robot_instance is None判断失效，实际旧实例已被销毁，重新赋值时会创建新的Robot实例，违反Webots一个控制器只能有一个Robot实例的规则。
2. Supervisor分支逻辑漏洞：reset方法创建新Supervisor实例时未检查类变量是否已存在，直接赋值可能导致重复创建；删除实例后也未置空_supervisor_instance类变量。
3. 拼写错误：self. robot.getRoot()中多了空格，会触发AttributeError，进而导致控制器异常退出。

修复方案 #

修复后的代码片段 #

_robot_instance = None
_supervisor_instance = None
def __init__(self, use_supervisor=False):
    self.use_supervisor = use_supervisor
    self.TIME_STEP = 32
    self.receiver = None
    self.webots_supervisor = None
    if use_supervisor:
        if Environment._supervisor_instance is None:
            Environment._supervisor_instance = Supervisor()
        self.webots_supervisor = Environment._supervisor_instance
        self.robot = self.webots_supervisor.getFromDef("agent1")
    else:
        if Environment._robot_instance is None:
            Environment._robot_instance = Robot()
        self.robot = Environment._robot_instance

def reset(self):
    print(f"Supervisor: {self.webots_supervisor}")
    # Release existing Robot/Supervisor instance if it exists
    if self.use_supervisor:
        if Environment._supervisor_instance is not None:
            self.webots_supervisor = None
            self.robot = None
            del Environment._supervisor_instance
            Environment._supervisor_instance = None  # 置空类变量
    else:
        if Environment._robot_instance is not None:
            self.robot = None
            del Environment._robot_instance
            Environment._robot_instance = None  # 置空类变量
    # Create a new Robot/Supervisor instance
    if self.use_supervisor:
        if Environment._supervisor_instance is None:  # 增加存在性检查
            Environment._supervisor_instance = Supervisor()
        self.webots_supervisor = Environment._supervisor_instance
        self.robot = self.webots_supervisor.getFromDef("agent1")
    else:
        if Environment._robot_instance is None:
            Environment._robot_instance = Robot()
        self.robot = Environment._robot_instance
    try:
        # 修复空格拼写错误
        root = (
            self.webots_supervisor.getRoot()
            if self.use_supervisor
            else self.robot.getRoot()
        )
        self.print_node_names(root)
    except AttributeError as e:
        print(f"Error getting nodes: {e}")

关键修复点 #

• 置空类变量：删除实例后必须将_robot_instance和_supervisor_instance置为None，确保下次创建时的判断逻辑正确。
• 增加实例存在性检查：Supervisor分支创建新实例前先检查类变量是否为空，避免重复创建。
• 修复拼写错误：去掉self. robot中的空格，改为self.robot，防止AttributeError导致控制器异常退出。

额外注意事项 #

• Webots中每个控制器进程只能创建一个Robot/Supervisor实例，多机器人场景下每个机器人对应独立的控制器进程，不要在同一个控制器里尝试创建多个Robot实例。
• 若使用Supervisor控制多机器人，确保通过getFromDef或getFromId正确获取各个机器人节点，而非重复创建Supervisor实例。

内容的提问来源于stack exchange，提问作者Kazmi