Backport(v1.19): test_out_exec_filter: fix flaky test on Windows (#5380)#5387
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**Which issue(s) this PR fixes**:
Fixes #
**What this PR does / why we need it**:
The `test 'using child processes by round robin'` in
`test_out_exec_filter.rb` was occasionally failing on Windows.
Like:
```
3) Failure: test: using child processes by round robin[with sections](ExecFilterOutputTest)
D:/a/fluentd/fluentd/test/plugin/test_out_exec_filter.rb:533:in 'block in <class:ExecFilterOutputTest>'
530:
531: assert_equal pid_list[0], events[0][2]['child_pid']
532: assert_equal pid_list[1], events[1][2]['child_pid']
=> 533: assert_equal pid_list[0], events[2][2]['child_pid']
534: assert_equal pid_list[1], events[3][2]['child_pid']
535: end
536:
<"8944"> expected but was
<"2728">
diff:
? 2728944
Error: <"8944"> expected but was
<"2728">.
```
The test previously assumed that the events would be processed and
returned in a strictly alternating order (e.g., A -> B -> A -> B).
However, on Windows, the overhead of process creation and unpredictable
I/O scheduling can cause the child processes to become ready and return
events out of order (e.g., A -> B -> B -> A), resulting in
false-positive test failures.
This commit fixes the flaky behavior by verifying the even distribution
of events rather than their strict chronological return order.
**Docs Changes**:
N/A
**Release Note**:
N/A
Signed-off-by: Shizuo Fujita <fujita@clear-code.com>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Watson1978
approved these changes
Jun 15, 2026
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Which issue(s) this PR fixes:
Backport #5380
Fixes #
What this PR does / why we need it:
The
test 'using child processes by round robin'intest_out_exec_filter.rbwas occasionally failing on Windows.Like:
The test previously assumed that the events would be processed and returned in a strictly alternating order (e.g., A -> B -> A -> B).
However, on Windows, the overhead of process creation and unpredictable I/O scheduling can cause the child processes to become ready and return events out of order (e.g., A -> B -> B -> A), resulting in false-positive test failures.
This commit fixes the flaky behavior by verifying the even distribution of events rather than their strict chronological return order.
Docs Changes:
N/A
Release Note:
N/A