engine_dispatch: Address stale failed tasks on dispatch

[cosmo0920]

Implemented the stale-task cleanup.

Changes:

• src/flb_engine_dispatch.c:72 now calls flb_task_users_release(task) after destroying the failed retry.
• Added tests/internal/engine_dispatch.c covering:
  • Releasing the last task owner and reusing its task-map slot.
  • Preserving a task with an active user.
  • Preserving a task with another pending retry.
• Registered the test in tests/internal/CMakeLists.txt.

Verification:

cmake -S . -B build -DFLB_TESTS_RUNTIME=On -DFLB_TESTS_INTERNAL=On
cmake --build build --target flb-it-engine_dispatch -j8
ctest --test-dir build -R "^(flb-it-engine_dispatch|flb-it-task_map)$" --output-on-failure

Result: both tests passed, 0 failures.

The regression test was also built and run temporarily without the production fix. It failed on the occupied task-map slot, retained task/chunk lists, and non-reused task ID. After restoring the fix, it passed.

No Python integration scenario covers this engine-dispatch lifecycle path.

Closes #12252.

---

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Testing
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• Example configuration file for the change
• Debug log output from testing the change

• Attached Valgrind output that shows no leaks or memory corruption was found

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Documentation

• Documentation required for this feature

Backporting

• Backport to latest stable release.

---

Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.

Summary by CodeRabbit

• Bug Fixes

  • Improved cleanup when retry processing fails, preventing retained task references.
  • Preserved correct task ownership and retry state during failed chunk flushing.
  • Retries now reschedule while attempts remain and are dropped only after reaching the retry limit.
  • Added accurate metrics for failed retries and dropped records and bytes.

• Tests

  • Added coverage for retry dispatch failures, cleanup, retry handling, and metric reporting.

[coderabbitai]

📝 Walkthrough

Walkthrough

The retry dispatch failure path now records retry and drop metrics, reschedules retries within the retry limit, and releases terminal retry state. Internal tests cover ownership, retry preservation, chunk registration, metrics, and task ID reuse.

Changes

Retry dispatch failure handling

Layer / File(s)	Summary
Handle retry flush failures src/flb_engine_dispatch.c	Failed chunk retrieval records output and drop metrics. The path reschedules retries with remaining attempts and releases terminal retry state at the retry limit.
Set up isolated retry failure state tests/internal/engine_dispatch.c, tests/internal/CMakeLists.txt	Test helpers create engine state, metrics, tasks, routes, retries, and chunks. CMake registers the test and adds the ChunkIO include directory.
Validate metrics and ownership cleanup tests/internal/engine_dispatch.c	Tests cover final-owner release, active-owner preservation, pending-retry preservation, retry rescheduling, metric updates, task and chunk cleanup, and task ID reuse.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Suggested reviewers: edsiper

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change to prevent stale failed tasks during engine dispatch.
Linked Issues check	✅ Passed	The changes reschedule failed retries, release orphaned tasks, preserve pending retries, update metrics, and add tests for issue #12252.
Out of Scope Changes check	✅ Passed	The metrics, build configuration, and internal tests directly support the retry dispatch fix and its validation.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch cosmo0920-plug-stale-failed-tasks-on-dispatch

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[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

tests/internal/engine_dispatch.c (1)

30-32: 📐 Maintainability & Code Quality | 🔵 Trivial | 💤 Low value

Use the required control-statement brace style.

Move the opening brace to the next line for each new if, else, while, and do block in this file. Line 30 is one example.

Proposed fix

-    if (ctx == NULL) {
+    if (ctx == NULL)
+    {
         return;
     }

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@tests/internal/engine_dispatch.c` around lines 30 - 32, Update the control
statements in engine_dispatch.c to place opening braces on the following line
for every if, else, while, and do block, including the block guarding ctx ==
NULL. Preserve all existing logic and formatting otherwise.

Source: Coding guidelines

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@tests/internal/engine_dispatch.c`:
- Around line 28-48: The test fixture must balance Winsock lifecycle management.
Update test_ctx_create to check the WSAStartup result and record successful
initialization in test_ctx; update test_ctx_destroy to call WSACleanup only when
initialization succeeded, after resource teardown, while preserving cleanup for
failed or partially initialized fixtures.

---

Nitpick comments:
In `@tests/internal/engine_dispatch.c`:
- Around line 30-32: Update the control statements in engine_dispatch.c to place
opening braces on the following line for every if, else, while, and do block,
including the block guarding ctx == NULL. Preserve all existing logic and
formatting otherwise.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

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📒 Files selected for processing (3)

• src/flb_engine_dispatch.c
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[coderabbitai]

🧹 Nitpick comments (1)

tests/internal/engine_dispatch.c (1)

89-94: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Use the required control-block brace style.

Move each opening brace to the next line.

• tests/internal/engine_dispatch.c#L89-L94: Move the if (ret != 0) opening brace.
• tests/internal/engine_dispatch.c#L139-L161: Move the counter-allocation failure-block opening brace.
• tests/internal/engine_dispatch.c#L166-L178: Move the metrics-allocation failure-block opening brace.
• tests/internal/engine_dispatch.c#L187-L190: Move the metrics cleanup-block opening brace.
• tests/internal/engine_dispatch.c#L236-L244: Move the metric null-check opening braces.
• tests/internal/engine_dispatch.c#L283-L292: Move the task-event-chunk and route-allocation failure-block opening braces.
• tests/internal/engine_dispatch.c#L333-L338: Move the output initialization failure-block opening brace.
• tests/internal/engine_dispatch.c#L385-L390: Move the output initialization failure-block opening brace.
• tests/internal/engine_dispatch.c#L451-L456: Move the output initialization failure-block opening brace.
• tests/internal/engine_dispatch.c#L470-L481: Move the allocation failure-block opening brace.

As per coding guidelines: “Put function opening braces on the next line.”

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@tests/internal/engine_dispatch.c` around lines 89 - 94, Apply the required
next-line brace style in tests/internal/engine_dispatch.c at lines 89-94,
139-161, 166-178, 187-190, 236-244, 283-292, 333-338, 385-390, 451-456, and
470-481: move each listed if/else failure, cleanup, null-check, and
allocation-block opening brace onto its own following line, without changing
control flow or behavior.

Source: Coding guidelines

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@tests/internal/engine_dispatch.c`:
- Around line 89-94: Apply the required next-line brace style in
tests/internal/engine_dispatch.c at lines 89-94, 139-161, 166-178, 187-190,
236-244, 283-292, 333-338, 385-390, 451-456, and 470-481: move each listed
if/else failure, cleanup, null-check, and allocation-block opening brace onto
its own following line, without changing control flow or behavior.

---

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📒 Files selected for processing (2)

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🚧 Files skipped from review as they are similar to previous changes (1)

• src/flb_engine_dispatch.c

[ku524]

Thanks for picking this up so quickly. I built this branch and confirmed it does close the leak.

One thing I would like your call on: releasing the task reaches flb_task_destroy(task, FLB_TRUE), which deletes the chunk file. A cio_chunk_up() failure is usually transient, so this discards records that the leak, bad as it was, kept on disk for a restart to flush.

I opened #12260 on top of this branch rather than only describing it. It keeps your fix and your drop accounting, and only spends one delivery attempt before giving up. With the default retry_limit of 1 the behaviour is identical to yours, so it engages only when the user has raised their retry budget.

Happy to close #12260 and move it into a review comment instead if you would rather keep this PR self-contained.

[cosmo0920]

Happy to close #12260 and move it into a review comment instead if you would rather keep this PR self-contained.

I merged your PR in this PR. Really appreciated to cooperate with you to address the issue.

[coderabbitai]

🧹 Nitpick comments (1)

src/flb_engine_dispatch.c (1)

130-138: 📐 Maintainability & Code Quality | 🔵 Trivial | 💤 Low value

Use the required block-brace layout.

The changed if blocks place the opening brace on the control-statement line. Move each opening brace to the following line.

• src/flb_engine_dispatch.c#L130-L138: move the retry-limit if opening brace to the next line.
• src/flb_engine_dispatch.c#L146-L148: move the reschedule-failure if opening brace to the next line.
• tests/internal/engine_dispatch.c#L540-L542: move the null-context if opening brace to the next line.
• tests/internal/engine_dispatch.c#L546-L549: move the output-init failure if opening brace to the next line.
• tests/internal/engine_dispatch.c#L556-L560: move the null-retry if opening brace to the next line.

As per coding guidelines, C control blocks must use braces on the following line.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/flb_engine_dispatch.c` around lines 130 - 138, Move each opening brace to
the line following its control statement without changing behavior: the
retry-limit and reschedule-failure if blocks in src/flb_engine_dispatch.c (lines
130-138 and 146-148), and the null-context, output-init failure, and null-retry
if blocks in tests/internal/engine_dispatch.c (lines 540-542, 546-549, and
556-560).

Source: Coding guidelines

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@src/flb_engine_dispatch.c`:
- Around line 130-138: Move each opening brace to the line following its control
statement without changing behavior: the retry-limit and reschedule-failure if
blocks in src/flb_engine_dispatch.c (lines 130-138 and 146-148), and the
null-context, output-init failure, and null-retry if blocks in
tests/internal/engine_dispatch.c (lines 540-542, 546-549, and 556-560).

---

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