Fix serial handler race condition Fixes #9

[semuadmin]

PyGPSClient Pull Request Template

Description

Amend serial_handler() to avoid race condition on null data stream.

Fixes # (issue)

#9

Testing

Please test all changes, however trivial, against the supplied unittest suite tests/test_*.py e.g. by executing the tests/testsuite.py
module or using your IDE's native Python unittest integration facilities.
Please describe any test cases you have amended or added to this suite to maintain >= 99% code coverage.

• Tested on all platforms Windows, Linux, MacOS, RPiOS

Checklist:

• My code follows the style guidelines of this project (see CONTRIBUTING.MD).
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• (if appropriate) I have added test cases to the tests/test_*.py unittest suite to maintain >= 99% code coverage.
• I have tested my code against the full tests/test_*.py unittest suite.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.
• I understand and acknowledge that the code will be published under a BSD 3-Clause license.

[semudev2]

Have tested with Python 3.8, 3.9 & 3.10 on Windows 10 & 11, Ubuntu 20 & 21, MacOS 11 & 12 and RaspiOS. Null stream and protocol filtering seem to work fine and consistently on all platforms.

FYI runs significantly slower on Python 3.10 / MacOS 12 but, as you've indicated, this is a MacOS tkinter problem rather than a pygpsclient problem).

[semuadmin]

@semudev2 out of interest, were you running on an M1 Mac? I hear the Python 10 tkinter performance is particularly poor on these?

Shame, as on the Dell XPS Ubuntu platform I normally use it flies (at least 3 times faster than an Intel Macbook Pro) - admittedly a compiled version of Python 3.10.2 with stable optimizations enabled. I did try compiling Python 3.10 with tkinter on MacOS but life is too short.