How to stream data to a Bokeh server using Holoviews - python-3.x

Question

I want to stream data generated by python to a webpage.
I came up with the following example, put together using examples from
https://holoviews.org/user_guide/Streaming_Data.html
and
http://holoviews.org/user_guide/Deploying_Bokeh_Apps.html
However I get a document lock error:
"'_pending_writes should be non-None when we have a document lock, and we should have the lock when the document changes'"
This is my example:
import numpy as np
import holoviews as hv
import holoviews.plotting.bokeh
import streamz
import streamz.dataframe
renderer = hv.renderer('bokeh')
from holoviews import opts
from holoviews.streams import Pipe, Buffer
hv.extension('bokeh')
source_df = streamz.dataframe.Random(freq='5ms', interval='100ms')
sdf = (source_df-0.5).cumsum()
raw_dmap = hv.DynamicMap(hv.Curve, streams=[Buffer(sdf.x)])
smooth_dmap = hv.DynamicMap(hv.Curve, streams=[Buffer(sdf.x.rolling('50ms').mean())])
fig = (raw_dmap.relabel('raw') * smooth_dmap.relabel('smooth')).opts(
opts.Curve(width=500, show_grid=True))
server = renderer.app(fig, show=True, new_window=True)
A page opens, figure shows up but is not updating. In my notebook I get the following error:
tornado.application - ERROR - Exception in callback functools.partial(<function wrap.<locals>.null_wrapper at 0x00000234E3CB9400>, <Future finished exception=RuntimeError('_pending_writes should be non-None when we have a document lock, and we should have the lock when the document changes')>)
Traceback (most recent call last):
File "C:\ProgramData\Anaconda3\lib\site-packages\tornado\ioloop.py", line 758, in _run_callback
ret = callback()
File "C:\ProgramData\Anaconda3\lib\site-packages\tornado\stack_context.py", line 300, in null_wrapper
return fn(*args, **kwargs)
File "C:\ProgramData\Anaconda3\lib\site-packages\tornado\ioloop.py", line 779, in _discard_future_result
future.result()
File "C:\ProgramData\Anaconda3\lib\site-packages\tornado\gen.py", line 1147, in run
yielded = self.gen.send(value)
File "C:\ProgramData\Anaconda3\lib\site-packages\streamz\dataframe\core.py", line 802, in _cb
yield source._emit((last, now, freq))
File "C:\ProgramData\Anaconda3\lib\site-packages\streamz\core.py", line 298, in _emit
r = downstream.update(x, who=self)
File "C:\ProgramData\Anaconda3\lib\site-packages\streamz\core.py", line 563, in update
return self._emit(result)
File "C:\ProgramData\Anaconda3\lib\site-packages\streamz\core.py", line 298, in _emit
r = downstream.update(x, who=self)
File "C:\ProgramData\Anaconda3\lib\site-packages\streamz\core.py", line 563, in update
return self._emit(result)
File "C:\ProgramData\Anaconda3\lib\site-packages\streamz\core.py", line 298, in _emit
r = downstream.update(x, who=self)
File "C:\ProgramData\Anaconda3\lib\site-packages\streamz\core.py", line 747, in update
return self._emit(result)
File "C:\ProgramData\Anaconda3\lib\site-packages\streamz\core.py", line 298, in _emit
r = downstream.update(x, who=self)
File "C:\ProgramData\Anaconda3\lib\site-packages\streamz\core.py", line 563, in update
return self._emit(result)
File "C:\ProgramData\Anaconda3\lib\site-packages\streamz\core.py", line 298, in _emit
r = downstream.update(x, who=self)
File "C:\ProgramData\Anaconda3\lib\site-packages\streamz\core.py", line 563, in update
return self._emit(result)
File "C:\ProgramData\Anaconda3\lib\site-packages\streamz\core.py", line 298, in _emit
r = downstream.update(x, who=self)
File "C:\ProgramData\Anaconda3\lib\site-packages\streamz\core.py", line 516, in update
result = self.func(x, *self.args, **self.kwargs)
File "C:\ProgramData\Anaconda3\lib\site-packages\holoviews\streams.py", line 436, in send
self.event(data=data)
File "C:\ProgramData\Anaconda3\lib\site-packages\holoviews\streams.py", line 375, in event
self.trigger([self])
File "C:\ProgramData\Anaconda3\lib\site-packages\holoviews\streams.py", line 156, in trigger
subscriber(**dict(union))
File "C:\ProgramData\Anaconda3\lib\site-packages\holoviews\plotting\plot.py", line 615, in refresh
self._trigger_refresh(stream_key)
File "C:\ProgramData\Anaconda3\lib\site-packages\holoviews\plotting\plot.py", line 624, in _trigger_refresh
self.update(key)
File "C:\ProgramData\Anaconda3\lib\site-packages\holoviews\plotting\plot.py", line 596, in update
item = self.__getitem__(key)
File "C:\ProgramData\Anaconda3\lib\site-packages\holoviews\plotting\plot.py", line 261, in __getitem__
self.update_frame(frame)
File "C:\ProgramData\Anaconda3\lib\site-packages\holoviews\plotting\bokeh\element.py", line 1944, in update_frame
self._update_ranges(element, ranges)
File "C:\ProgramData\Anaconda3\lib\site-packages\holoviews\plotting\bokeh\element.py", line 657, in _update_ranges
self._shared['x'], self.logx, streaming)
File "C:\ProgramData\Anaconda3\lib\site-packages\holoviews\plotting\bokeh\element.py", line 702, in _update_range
axis_range.trigger(k, old, new)
File "C:\ProgramData\Anaconda3\lib\site-packages\bokeh\model.py", line 599, in trigger
super(Model, self).trigger(attr, old, new, hint=hint, setter=setter)
File "C:\ProgramData\Anaconda3\lib\site-packages\bokeh\util\callback_manager.py", line 143, in trigger
self._document._notify_change(self, attr, old, new, hint, setter, invoke)
File "C:\ProgramData\Anaconda3\lib\site-packages\bokeh\document\document.py", line 1004, in _notify_change
self._trigger_on_change(event)
File "C:\ProgramData\Anaconda3\lib\site-packages\bokeh\document\document.py", line 1099, in _trigger_on_change
self._with_self_as_curdoc(invoke_callbacks)
File "C:\ProgramData\Anaconda3\lib\site-packages\bokeh\document\document.py", line 1112, in _with_self_as_curdoc
return f()
File "C:\ProgramData\Anaconda3\lib\site-packages\bokeh\document\document.py", line 1098, in invoke_callbacks
cb(event)
File "C:\ProgramData\Anaconda3\lib\site-packages\bokeh\document\document.py", line 668, in <lambda>
self._callbacks[receiver] = lambda event: event.dispatch(receiver)
File "C:\ProgramData\Anaconda3\lib\site-packages\bokeh\document\events.py", line 244, in dispatch
super(ModelChangedEvent, self).dispatch(receiver)
File "C:\ProgramData\Anaconda3\lib\site-packages\bokeh\document\events.py", line 126, in dispatch
receiver._document_patched(self)
File "C:\ProgramData\Anaconda3\lib\site-packages\bokeh\server\session.py", line 214, in _document_patched
raise RuntimeError("_pending_writes should be non-None when we have a document lock, and we should have the lock when the document changes")
RuntimeError: _pending_writes should be non-None when we have a document lock, and we should have the lock when the document changes
Any clues what I'm doing wrong?
Kind regards

Answer 1

I changed the last line to renderer.server_doc(fig), saved everything as a notebook named test.ipynb. In the command prompt, I ran >bokeh serve --show .\test.ipynb. The server is up and the streaming of data is shown in the browser as expected.
import numpy as np
import holoviews as hv
import holoviews.plotting.bokeh
import streamz
import streamz.dataframe
renderer = hv.renderer('bokeh')
from holoviews import opts
from holoviews.streams import Pipe, Buffer
hv.extension('bokeh')
source_df = streamz.dataframe.Random(freq='5ms', interval='100ms')
sdf = (source_df-0.5).cumsum()
raw_dmap = hv.DynamicMap(hv.Curve, streams=[Buffer(sdf.x)])
smooth_dmap = hv.DynamicMap(hv.Curve, streams=[Buffer(sdf.x.rolling('50ms').mean())])
fig = (raw_dmap.relabel('raw') * smooth_dmap.relabel('smooth')).opts(
opts.Curve(width=500, show_grid=True))
renderer.server_doc(fig)