What is the event sent when a plot is refreshed

Community Support
1

hi
i want to add a callback after a figure is refreshed when the associated column data source has its data changed.
i dont think cds.on_change(‘data’, cb) is the correct way because i want an event launched from the plot on client side.
thanks

2

There is not currently such any event exposed for plot refresh. If you can describe what you are actually trying to accomplish at a high level, without assuming a particular solution (e.g. a “plot refresh” event), there might be other alternatives we can suggest.

3

I want to plot last N samples of a data stream. I don’t want to use a push model, i.e updating cds data every seconds. I want to use a pull model, updating cds only when the plot has finished to display the previous data.

4

You could use an AjaxDataSource to poll a remote endpoint on a fixed interval, I am afraid that is the closest suggestion I have.

5

I’m not sure if I correctly understand you but MAYBE, this same post is relevant to you: Scatter markers time series plot interacting too slow - #6 by Cosmidark

6

thanks Bryan
I think ajax solution is too complex to implement on my side.
Finally, i only need the event sent when a plot is updated in the browser.
If i does not exist, is it complicated to implement it ? Do you know where i should look first in the bokeh source tree ?
i found source.js_on_change(‘streaming’, cb). May be is good enough for me.
In the documentation, i saw the following steps in the propagation of an event
‘’
user invokes Document API
→ Document API triggers event objects
→ registered callbacks are executed
→ Sesssion callback generates JSON message from event object
→ Session sends JSON message over websocket

Session recieves JSON message over websocket
→ Document calls event.handle_json
→ handle_json invokes appropriate Document API
→ Document API triggers event objects
→ registered callbacks are executed
→ Session callback suppresses outgoing event
‘’
when i do a cds.data or a cds.stream(), does it mean that all these steps have been executed synchronously ?
or is there a stack or queue somewhere between two steps ? I mean if i do plenty of cds.data, where a ‘stack overflow’ appears ?
thanks

7

Finally, i only need the event sent when a plot is updated in the browser.

As I said above, this does not exist.

If i does not exist, is it complicated to implement it ? Do you know where i should look first in the bokeh source tree ?

It’s not enormous work, but it is also not trivial. As an example, here is the PR the added the RangesUpdate event:

Add RangesUpdate event by bryevdv · Pull Request #11125 · bokeh/bokeh · GitHub

Adding a “render finished” event, including tests, would probably be a comparable effort. Note that:

  • Given our current release cadence, this new feature would not make it into a published release for another 3-6 months.
  • There would need to be core dev agreement that it is good to add at all.

i found source.js_on_change(‘streaming’, cb).

Where? This was a mostly experimental feature in old versions of Bokeh. AFAIK it does not exist any longer in modern versions. cc @mateusz

when i do a cds.data or a cds.stream(), does it mean that all these steps have been executed synchronously ?

Bokeh throttles the rendering step and combines updates within the throttle window, so no.

To be honest, if eventing exactly on plot render is a hard and fast requirement for you, you might want to look at other tools.

8

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