Hi, ROS users,<div><br></div><div>I&#39;m trying to send large amount of data like image data with 100hz through topic messages.</div><div>But it seems that subscriber callback is called 4 times in a batch in 25hz at maximum.</div>

<div>I&#39;ve managed to reproduce this problem with the following simple code.</div><div><br></div><div>-- publisher start --</div><div><div>#include &lt;iostream&gt;</div><div>#include &lt;fstream&gt;</div><div>#include &lt;boost/date_time.hpp&gt;</div>

<div>#include &lt;ros/ros.h&gt;</div><div>#include &lt;ros/console.h&gt;</div><div>#include &lt;std_msgs/String.h&gt;</div><div>#include &lt;sstream&gt;</div></div><div><br></div><div><div>using namespace std;</div></div>

<div><br></div><div><div>int main(int argc, char **argv) {</div><div>  ros::init(argc, argv, &quot;talker&quot;);</div><div>  ros::NodeHandle n;</div><div>  ros::Publisher chatter_pub = n.advertise&lt;std_msgs::String&gt;(&quot;chatter&quot;, 1000);</div>

<div>  ros::Rate loop_rate(100);</div><div>  int count = 0;</div><div>  while (ros::ok() &amp;&amp; count &lt; 2000) {</div><div>    std_msgs::String msg;</div><div>    std::stringstream ss;</div><div>    for (int i = 0; i &lt; 100; ++i) {                // to make large amount of data</div>

<div>      ss &lt;&lt; &quot;hello world &quot; &lt;&lt; count;</div><div>    }</div><div>    msg.data = ss.str();</div><div>    chatter_pub.publish(msg);</div><div><br></div><div>    ros::spinOnce();</div><div>    loop_rate.sleep();</div>

<div>    ++count;</div><div>  }</div><div><br></div><div>  return 0;</div><div>}</div></div><div>-- publisher end --</div><div><br></div><div>-- subscriber start --</div><div><div>#include &lt;boost/date_time.hpp&gt;</div>

<div>#include &lt;ros/ros.h&gt;</div><div>#include &lt;ros/callback_queue.h&gt;</div><div>#include &lt;ros/console.h&gt;</div><div>#include &lt;std_msgs/String.h&gt;</div><div>#include &lt;sstream&gt;</div><div><br></div>

<div>using namespace std;</div><div><div><br></div><div>boost::posix_time::ptime curTime;</div><div>boost::posix_time::ptime prevTime;</div></div></div><div><div><br></div><div>void printLogTime() {</div><div>  curTime = boost::posix_time::microsec_clock::local_time();</div>

<div>  boost::posix_time::time_duration td = curTime - prevTime;</div><div>  cout &lt;&lt; td.total_microseconds() &lt;&lt; endl;</div><div>  prevTime = curTime;</div><div>}</div></div><div><br></div><div><div>void chatterCallback(const std_msgs::String::ConstPtr&amp; msg) {</div>

<div>  printLogTime();</div><div>}</div><div><br></div><div>int main(int argc, char **argv) {</div><div>  ros::init(argc, argv, &quot;listener&quot;);</div><div>  ros::NodeHandle n;</div><div>  ros::Subscriber sub = n.subscribe(&quot;chatter&quot;, 1000, chatterCallback);</div>

<div>  ros::spin();</div><div><br></div><div>  return 0;</div><div>}</div></div><div>-- subscriber end --</div><div><br></div><div>Subscriber&#39;s console log is as follows</div><div>---</div><div><div>9223372036854775806</div>

<div>9911</div><div>9986</div><div>9996</div><div>10001</div><div>10002</div><div>9995</div><div>9999</div><div>10002</div><div>10017</div><div>9988</div><div>9994</div><div>10000</div><div>10002</div><div>9998</div><div>

10002</div><div>10000</div><div>9993</div><div><b><font color="#3333ff">39598</font></b></div><div><b><font color="#3333ff">28</font></b></div><div><b><font color="#3333ff">38</font></b></div>
<div><b><font color="#3333ff">39932</font></b></div><div><b><font color="#3333ff">28</font></b></div><div><b><font color="#3333ff">47</font></b></div>
<div><b><font color="#3333ff">23</font></b></div><div><b><font color="#3333ff">39900</font></b></div><div><b><font color="#3333ff">28</font></b></div>
<div><b><font color="#3333ff">45</font></b></div><div><b><font color="#3333ff">24</font></b></div><div><b><font color="#3333ff">39906</font></b></div>
<div><b><font color="#3333ff">26</font></b></div><div><b><font color="#3333ff">46</font></b></div><div><b><font color="#3333ff">23</font></b></div>
<div><b><font color="#3333ff">39903</font></b></div><div><b><font color="#3333ff">26</font></b></div><div><b><font color="#3333ff">48</font></b></div>
<div><b><font color="#3333ff">24</font></b></div></div><div>---</div><div><br></div><div>As you can see, subscriber callback is called as expected, but is called 4 times in a batch</div><div>after sometime.</div>
<div><br></div><div>If I change ros::spin() as follows,</div><div><br></div><div>--- alternate loop --</div><div><div>  ros::Rate r(100);</div><div>  while (ros::ok()) {</div><div>    r.sleep();</div><div>    ros::getGlobalCallbackQueue()-&gt;callOne(ros::WallDuration(0.001));</div>

<div>  }</div></div><div>---</div><div><br></div><div>then, this problem does not happen.</div><div><br></div><div>subscriber&#39;s log with alternate loop</div><div>---</div><div><div>9223372036854775806</div><div>9905</div>

<div>9992</div><div>10008</div><div>9993</div><div>9997</div><div>10004</div><div>9997</div><div>10001</div><div>10000</div><div>10004</div><div>9998</div><div>9995</div><div>10009</div><div>9997</div><div>9998</div><div>

10014</div><div>9998</div><div>9999</div><div>10000</div><div>10005</div><div>9997</div><div>9995</div><div>10010</div><div>9995</div><div>9999</div><div>10002</div><div>10000</div><div>9994</div><div>10002</div><div>10004</div>

<div>9998</div><div>10000</div><div>10007</div><div>9991</div><div>10002</div><div>10001</div><div>9999</div><div>9997</div><div>10000</div><div>10006</div><div>9997</div><div>10010</div><div>9991</div><div>9998</div><div>

10000</div><div>10002</div><div>9999</div><div>9997</div><div>9999</div><div>10006</div><div>9998</div><div>9999</div><div>10001</div><div>10001</div><div>9998</div><div>9999</div></div><div>...</div><div>---</div><div><br>

</div><div>&quot;rostopic hz&quot; command also suffers from this problem.</div><div>---</div><div><div>$ rostopic hz /chatter</div><div>subscribed to [/chatter]</div><div>average rate: 98.983</div><div>        <b><font color="#3333ff">min: 0.000s max: 0.040s</font></b> std dev: 0.01574s window: 97</div>

<div>average rate: 99.500</div><div>        <font color="#3333ff"><b>min: 0.000s max: 0.040s</b></font> std dev: 0.01654s window: 197</div><div>average rate: 99.668</div><div>        <font color="#3333ff"><b>min: 0.000s max: 0.040s</b></font> std dev: 0.01680s window: 297</div>

<div>average rate: 99.755</div><div>        <font color="#3333ff"><b>min: 0.000s max: 0.040s</b></font> std dev: 0.01692s window: 397</div><div>average rate: 99.807</div><div>        <font color="#3333ff"><b>min: 0.000s max: 0.040s</b></font> std dev: 0.01699s window: 497</div>

<div>average rate: 99.839</div><div>        <font color="#3333ff"><b>min: 0.000s max: 0.040s</b></font> std dev: 0.01704s window: 597</div></div><div>---</div><div><br></div><div>Periodic transmission of topic messages with strong timing constraints is important </div>
<div>for my application but the &#39;alternate loop&#39; solution doesn&#39;t allow me to use different hz </div><div>between publisher and subscriber, which is not a perfect solution for my application.</div><div><br></div>
<div><div>Is there any way to adjust latency of subscriber callback?</div>
</div><div><br></div><div>Thanks a lot!</div><div><br></div><div>- Yoonsoo</div><div><br></div>