test: ensure logs are flushed before reading them #33198

1. 
   stickies-v commented at 2:45 pm on August 15, 2025: contributor

   Should fix #33195 (still testing, trying to reproduce locally, draft until then)

   Logging to file is unbuffered (src), but is not blocked by flushing. Generally, that seems desireable, but it can be problematic for tests.

   #33195 observes intermittent failure of the TestLogFromLocation() function (see comment for more details), where we write and read to/from file in quick succession.

   This PR introduces a Logger::FlushDebugFile() method, and uses it in the test-only ReadDebugLogLines() function. As such, this PR should not change any non-test behaviour or performance.

2. log: add FlushDebugFile method

   This function blocks until the file is actually flushed, preventing
   race conditions when accessing m_fileout by just relying on it being
   unbuffered.

   17aba8c0e1
3. test: ensure logs are flushed before reading them

   Prevents race conditions, such as e.g. in
   https://github.com/bitcoin/bitcoin/issues/33195

   e7758593ba
4. DrahtBot added the label Tests on Aug 15, 2025
5. 
   DrahtBot commented at 2:45 pm on August 15, 2025: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33198.

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   See the guideline for information on the review process. A summary of reviews will appear here.

6. hebasto added this to the milestone 30.0 on Aug 15, 2025
7. 
   stickies-v commented at 4:15 pm on August 18, 2025: contributor

   This PR seems to be on the wrong track, see this comment and further. Closing.
8. stickies-v closed this on Aug 18, 2025

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stickies-v DrahtBot

Labels
Tests

Milestone
30.0