Syslog monitor memory leak fix

[alesnovak-s1]

After several attempts to make syslog monitor threading robust and memory efficient, I decided to implement a simple solution of bounded ThreadingMixin. A better candidate might seem to be a ThreadPoolExecutor, but it proved to be very memory hungry.

The reason for using threads in the first place is:

• UDP - avoid loosing too many sockets
• TCP - avoid blocking on unfinished and not yet closed requests

The ideal solution would be to get right of our rigid in-house implementation based on BaseServer and etither

• use socket.poll() on all open sockets or
• use async library for hansling sockets, i.e. tornado. But such a big refactoring is not a priority at the moment.

[github-actions[bot]]

Test Results

     20 files  ±0       20 suites  ±0   30m 23s :stopwatch: - 2m 52s 1 486 tests +1  1 466 :heavy_check_mark: +1    20 :zzz: ±0  0 :x: ±0  7 101 runs  +5  6 874 :heavy_check_mark: +3  227 :zzz: +2  0 :x: ±0 

Results for commit bdaa12e8. ± Comparison against base commit 47390e30.

:recycle: This comment has been updated with latest results.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 87.80488% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 78.31%. Comparing base (b514d71) to head (568b57d). Report is 5 commits behind head on master.

:exclamation: Current head 568b57d differs from pull request most recent head bdaa12e. Consider uploading reports for the commit bdaa12e to get more accurate results

Additional details and impacted files

[](https://app.codecov.io/gh/scalyr/scalyr-agent-2/pull/1248?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scalyr) ```diff @@ Coverage Diff @@ ## master #1248 +/- ## =========================================== + Coverage 54.83% 78.31% +23.48% =========================================== Files 51 176 +125 Lines 18666 42929 +24263 Branches 3294 4775 +1481 =========================================== + Hits 10235 33617 +23382 - Misses 7232 8237 +1005 + Partials 1199 1075 -124 ``` | [Files](https://app.codecov.io/gh/scalyr/scalyr-agent-2/pull/1248?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scalyr) | Coverage Δ | | |---|---|---| | [scalyr\_agent/builtin\_monitors/thread\_pool\_dummy.py](https://app.codecov.io/gh/scalyr/scalyr-agent-2/pull/1248?src=pr&el=tree&filepath=scalyr_agent%2Fbuiltin_monitors%2Fthread_pool_dummy.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scalyr#diff-c2NhbHlyX2FnZW50L2J1aWx0aW5fbW9uaXRvcnMvdGhyZWFkX3Bvb2xfZHVtbXkucHk=) | `0.00% <ø> (ø)` | | | [tests/unit/builtin\_monitors/syslog\_monitor\_test.py](https://app.codecov.io/gh/scalyr/scalyr-agent-2/pull/1248?src=pr&el=tree&filepath=tests%2Funit%2Fbuiltin_monitors%2Fsyslog_monitor_test.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scalyr#diff-dGVzdHMvdW5pdC9idWlsdGluX21vbml0b3JzL3N5c2xvZ19tb25pdG9yX3Rlc3QucHk=) | `98.31% <100.00%> (ø)` | | | [scalyr\_agent/builtin\_monitors/syslog\_monitor.py](https://app.codecov.io/gh/scalyr/scalyr-agent-2/pull/1248?src=pr&el=tree&filepath=scalyr_agent%2Fbuiltin_monitors%2Fsyslog_monitor.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scalyr#diff-c2NhbHlyX2FnZW50L2J1aWx0aW5fbW9uaXRvcnMvc3lzbG9nX21vbml0b3IucHk=) | `68.59% <83.33%> (+16.31%)` | :arrow_up: | | [scalyr\_agent/builtin\_monitors/thread\_pool.py](https://app.codecov.io/gh/scalyr/scalyr-agent-2/pull/1248?src=pr&el=tree&filepath=scalyr_agent%2Fbuiltin_monitors%2Fthread_pool.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scalyr#diff-c2NhbHlyX2FnZW50L2J1aWx0aW5fbW9uaXRvcnMvdGhyZWFkX3Bvb2wucHk=) | `85.19% <83.33%> (+3.19%)` | :arrow_up: | ... and [165 files with indirect coverage changes](https://app.codecov.io/gh/scalyr/scalyr-agent-2/pull/1248/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scalyr)