[ENH] ConcurrentWidgetMixin: Cancel task on input change

[VesnaT]

Issue

ConcurrentWidgetMixin subclasses don't stop computation when an input changes.

Description of changes

Set invalidated widget state (instead of blocking state) when stopping/starting the task.

Includes

• Code changes
• Tests
• Documentation

[codecov]

Codecov Report

Merging #4219 into master will decrease coverage by 0.02%.
The diff coverage is 95.83%.

@@            Coverage Diff            @@
##           master   #4219      +/-   ##
=========================================
- Coverage   86.23%   86.2%   -0.03%     
=========================================
  Files         396     396              
  Lines       70643   70635       -8     
=========================================
- Hits        60918   60890      -28     
- Misses       9725    9745      +20

[ales-erjavec]

If i connect File -> t-SNE, and load iris.tab then housing.tab, then move focus (tab) to the 'Recent' combo box and spam the down arrow key, eventually I get a:

Traceback (most recent call last):
  File "/Users/aleserjavec/workspace/orange3/Orange/widgets/unsupervised/owtsne.py", line 551, in on_partial_result
    self.__ensure_task_same_for_pca(task)
  File "/Users/aleserjavec/workspace/orange3/Orange/widgets/unsupervised/owtsne.py", line 516, in __ensure_task_same_for_pca
    assert task.data is self.data
AssertionError

[janezd]

Please rebase to current master.

[ales-erjavec]

numpy.testing should not be used outside of unittests.

I am assuming the cause of this assert violation is a check that the data is the same upon receiving the input but only after having already updated self.data.

If that is the case I would just remove the assert.

[VesnaT]

It's replaced with (task.data.X == self.data.X).all()

EDIT: I'll remove it.