[andersvw]

Notes

With a buffer size set, the writer sends only full buffers, and ~Writer joined the sending thread and dropped whatever was left, so a process that exits before it fills one buffer never sends those meters. ~Writer now sends the rest of the buffer, under the write mutex, after the sending thread has joined. NDrive hit this with a startup-failure counter that its sidecar records a second before it exits.

Testing

$ ctest --output-on-failure   # clang 19, Debug
100% tests passed, 0 tests failed out of 17

Just the new test without the source code fix:

$ ./writer_test
test_writer.cpp:51: Failure
nothing was sent at exit: Resource temporarily unavailable
[  FAILED  ] WriterShutdownDeathTest.SendsBufferedLinesAtExit

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