main thread error prints are in random order

[jtmoon79]

Problem

Running s4 with multiple errant files will print errors like ERROR: something something for file ./logs/... (which is expected). These lines printed to stderr occur in a varying order for subsequent runs of s4. This degrades the quality of comparison done in ./tools/compare-current-and-expected/compare.sh.

To Reproduce

1. in ./tools/compare-current-and-expected/common.sh
   comment out the line filters ERROR: strings
2. run ./tools/compare-current-and-expected/update.sh
3. run ./tools/compare-current-and-expected/compare.sh until failure

The lines starting with ERROR: are in varying order.

Another simpler approach:

1. run s4 manually with known errant files

   find ./logs/other/tests/ -name 'invalid*' -or -name 'empty*' | sort \
      | ./target/release/s4 - 1>/dev/null
   

Environment:

• OS: ubuntu 22 (should occur on any OS)
• s4 version: e75daad

[jtmoon79]

This may be similar cause as #213 where multi-threaded design is causing this behavior. However, it needs investigation to see if it's possible to accumulate errors for "the first round of processing" and then print errors along with normal prints in order of file path. Thinking about it, why isn't this already happening?