Catch KeyError as another possible failure of multithreading

[vyasr]

Description

When multithreading support is disabled, it is possible for operations on synced dicts to fail with a KeyError (as well as the other errors that were already being caught), so the multithreading test now catches that failure. Note that this is a bug in the test only, not in signac itself.

Motivation and Context

PyPy3 tests of multithreading have been failing due to this omission (see #705 and #706). Additionally, once this failure occurs, the buffer is in an invalid state, so future multithreading tests can fail in unpredictable ways. I reproduced the issue by running test_json_buffered_collection.py::TestBufferedJSONDictWriteConcern::test_multithreaded using pytest-repeat to run the test 100 times. I invariably observed failures within this number of tests. I then verified that catching the KeyError and clearing the collection prevents the error by running the test a few times with 1000 repeats (with pytest-xdist just to make sure that #705 was safe). I observed no further errors.

Types of Changes

• Documentation update
• Bug fix
• New feature
• Breaking change¹

¹The change breaks (or has the potential to break) existing functionality.

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• My name is on the list of contributors.
• My code follows the code style guideline of this project.
• The changes introduced by this pull request are covered by existing or newly introduced tests.

If necessary:

• I have updated the API documentation as part of the package doc-strings.
• I have created a separate pull request to update the framework documentation on signac-docs and linked it here.
• I have updated the changelog and added all related issue and pull request numbers for future reference (if applicable). See example below.

[codecov]

Codecov Report

Merging #710 (43e89eb) into master (2c6da9f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #710   +/-   ##
=======================================
  Coverage   78.54%   78.54%           
=======================================
  Files          65       65           
  Lines        7141     7141           
  Branches     1565     1565           
=======================================
  Hits         5609     5609           
  Misses       1228     1228           
  Partials      304      304           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2c6da9f...43e89eb. Read the comment docs.

[bdice]

@vyasr What did the KeyError say in the message/error value?

[bdice]

LGTM, this is probably safe to merge if it fixed the issue locally for you. I am curious what the KeyError said.

[vyasr]

@bdice have a look at the failure on #705, you can see the failure there. Here's a specific run.