ros::spin()

`ros::spin()` 是一个ROS的函数，它的作用是进入ROS的消息循环中，等待接收来自ROS的消息，并且调用相应的回调函数处理这些消息。在ROS节点中，当调用了 `ros::spin()` 函数后，节点就开始了消息的接收和处理。当ROS节点接收到消息后，它会调用相应的回调函数来处理这些消息，处理完毕后再次进入消息循环等待下一条消息的到来。在ROS节点中，`ros::spin()` 函数通常在节点初始化完成后调用，一直运行直到节点被关闭。

相关问题

ros::spinOnce() ros::spin()

In ROS, there are two commonly used functions for handling callbacks: ros::spinOnce() and ros::spin().

ros::spinOnce() allows ROS to process any pending callbacks once, but then returns control to the calling thread. This is useful when you have a loop that needs to keep running, but you need to periodically check for new data or events.

ros::spin(), on the other hand, is a blocking call that does not return control to the calling thread until the node is shut down. This is useful when you have a node that needs to run continuously and respond to events or data as they come in.

In general, you should use ros::spinOnce() if you have a loop that needs to keep running, and ros::spin() if you have a node that needs to run continuously. However, there are some cases where you may need to use both functions together, such as if you have multiple nodes running in the same process.

ros::Timer timer = nh.createTimer(ros::Duration(0), creat_callback); ros::spin()

这段代码创建了一个周期为0秒的ROS计时器，并指定当计时器超时时调用名为`creat_callback`的回调函数。接着，通过调用`ros::spin()`函数来使ROS节点进入自循环状态，等待来自ROS系统的事件（例如计时器超时事件、消息到达事件等）。在自循环状态下，ROS会不断地检查是否有事件发生，如果有则会调用相应的回调函数来处理事件。因为计时器的周期为0秒，所以它会立即超时并执行回调函数。而通过调用`ros::spin()`函数，ROS节点会一直等待事件的发生，直到节点被关闭。所以这段代码会在计时器超时后执行回调函数，并一直等待事件的发生，直到节点被关闭。