Pushing a chart to the the client using Wt - server-push

Question

I am using server push in Wt and I am trying to push a new chart with the following code:
Wt::WApplication::UpdateLock uiLock(app);
if (uiLock){
chart_ste = new ScatterPlotExample(this,10*asf.get_outputSamplingRate());
app->triggerUpdate();
}
but it waits for the program to end and then it prints it whereas the following code in the same program pushes the word "Demokritus every 0.5 secs as it should do:
for (int i=0; i<10; i++)
{
boost::this_thread::sleep(boost::posix_time::milliseconds(500));
Wt::WApplication::UpdateLock uiLock(app);
if (uiLock) {
showFileName = new WText(this);
showFileName->setText(boost::lexical_cast<std::string>("Demokritus"));
app->triggerUpdate();
}
}
What might be my mistake?

Answer 1

The documentation for triggerUpdate mentions that "The update is not immediate, and thus changes that happen after this call will equally be pushed to the client." If the changes are not immediate, it could be that the first piece of code continuously tries to push updates as fast as your CPU will allow it, so it never gets to the server because a new update overwrites the last and it begins waiting again. Try adding boost::this_thread::sleep(boost::posix_time::milliseconds(500)); to the first piece of code to see if that helps.
I've done a project once where I needed to update a chart every second with new data and had a very similar setup to yours. I put in the sleep from the start because I did not want my boost thread to use too much CPU.
Also, it is unclear if the first piece of code is in a bigger loop, if it is, you probably shouldn't make a new chart every time, but create it before hand and then update it with data. I hope some of this helps.