Asynchronous "show/hide" TexteArea works in the classic Notebook but doesn't in JupyterLab

[nleclercq]

In our use case, the idea is to popup an TextArea when an error occurred in an asynchronous process and to hide it when the error condition disappears. The implementation uses a dedicated Output to display the TextArea when an error occurred. The Output.clear_output is then called to remove the TextArea when the problem is fixed.

In the following code, the asynchronous activity is simulated by a thread. This works smoothly in the classic Notebook but doesn't behave as expected in JupyterLab : the TextArea doesn't show up or remains displayed. The ipywidgets Jupyterlab extension is (obviously) properly installed and works as expected in other contexts.

Here is the Conda configuration I'm using:

ipykernel       5.3.1       py37h43977f1_0  conda-forge
ipython         7.16.1      py37h43977f1_0  conda-forge
ipython_genutil     0.2.0       py_1        conda-forge
ipywidgets      7.5.1       py_0        conda-forge
jupyter_client      6.1.5       py_0        conda-forge
jupyter_core        4.6.3       py37hc8dfbb8_1  conda-forge
jupyterlab      2.1.5       py_0        conda-forge
jupyterlab_server   1.2.0       py_0        conda-forge
notebook        6.0.3       py37hc8dfbb8_0  conda-forge 
python          3.7.7       hcff3b4d_5 
widgetsnbextension  3.5.1       py37_0      conda-forge
traitlets       4.3.3       py37hc8dfbb8_1  conda-forge

Here is some code reproducing the problem:

import threading
import time
from IPython.display import display
import ipywidgets as widgets

class AsyncErrorArea(object):

    def __init__(self):
        self.cnt = 0
        self.err = False
        self.wta = widgets.Textarea(layout = widgets.Layout(flex='1 1 auto', width='auto'),
                                    placeholder='You should not see this TextArea!',
                                    disabled=True) 
        weo_layout = widgets.Layout(flex='1 1 auto', width='auto')
        weo_layout.border = "1px solid grey"
        self.weo = widgets.Output(layout=weo_layout)
        display(self.weo)

    def show_error(self, err):
        try:
            self.err = True
            txt = "Oops, the following error occurred: " + err
            self.wta.value = txt
            self.wta.rows = 2
            with self.weo:
                display(self.wta)
            self.weo.layout.border = ""
        except Exception as e:
            print(e)

    def hide_error(self):
        try:
            self.err = False
            self.wta.value = ""
            self.weo.clear_output()
            self.weo.layout.border = "1px solid grey"
        except Exception as e:
            print(e)

    def simul_activity(self):
        try:
            while not self.exit_requested:
                self.cnt += 1
                if not self.cnt % 3:
                    self.show_error("error #{}".format(self.cnt))
                elif self.err:
                    self.hide_error()
                time.sleep(1.)
        except Exception as e:
            print(e)

    def start(self):
        self.exit_requested = False
        self.thread = threading.Thread(target=self.simul_activity)
        self.thread.start()

    def exit(self):
        self.exit_requested = True
        self.thread.join()

aea = AsyncErrorArea()
aea.start()

aea.exit()

[nleclercq]

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