Publisher sleep forever using roslaunch

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When I ran a simple publisher in the tutorial ( http://wiki.ros.org/ROS/Tutorials/Wri... ). I got a problem that if I ran it through launch file, the node will sleep forever. But if I ran it through rosrun [packagename] talker, it works fine. My launch file looks like this, can anyone help me?

<launch>

<master auto="start"/>

<param name="use_sim_time" value="true"/>

<node pkg="hybridAstar" type="talker" name="talker" output="screen"/>

</launch>