Fix corrupted JSONL metrics file due to concurrent writes#19011
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talorabr
requested review from
Ying1123,
hnyls2002,
merrymercy and
xiezhq-hermann
as code owners
Summary of ChangesHello @talorabr, I'm Gemini Code Assist1! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed! This pull request addresses a critical data integrity issue where concurrent writes to JSONL metrics files could lead to corruption. By introducing a read-write lock, the system now safely handles parallel write operations, ensuring that all exported metrics data remains valid and uncorrupted, which is crucial for reliable performance monitoring. Highlights
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Code Review
This pull request correctly addresses a potential race condition that could lead to corrupted JSONL metrics files from concurrent writes. The use of a lock to serialize file access within FileRequestMetricsExporter.write_record is the appropriate solution. The implementation is clean and effectively resolves the issue. My review includes a suggestion to simplify the locking mechanism by using a standard asyncio.Lock instead of an RWLock, as only exclusive write access is currently required.
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| from sglang.srt.managers.io_struct import EmbeddingReqInput, GenerateReqInput | ||
| from sglang.srt.server_args import ServerArgs | ||
| from sglang.srt.utils.aio_rwlock import RWLock |
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Since only the writer lock is used in FileRequestMetricsExporter, a simpler asyncio.Lock would suffice and be slightly more direct. You can remove this import and use the asyncio module, which is already imported.
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@talorabr Can we replace with a simpler asyncio.Lock as suggested
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| # File handler state management | ||
| self._current_file_handler = None | ||
| self._current_file_lock = RWLock() |
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Using a standard asyncio.Lock is simpler here since there are no concurrent read operations. While RWLock is not incorrect, asyncio.Lock is more idiomatic for purely exclusive access. If you anticipate adding concurrent read-only operations in the future, keeping RWLock is reasonable.
| self._current_file_lock = RWLock() | |
| self._current_file_lock = asyncio.Lock() |
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| # Ensure correct file handler is open for current hour | ||
| self._ensure_file_handler(hour_suffix) | ||
| async with self._current_file_lock.writer_lock: |
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To align with the suggestion of using asyncio.Lock, this should be updated to acquire the lock directly.
| async with self._current_file_lock.writer_lock: | |
| async with self._current_file_lock: |
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Do we have example of json file before/after this PR as comparison |
sglang-request-metrics-20260222_04.after.log In the |
2 participants
Motivation
When using sglang server with
--export-metrics-to-file --export-metrics-to-file-dir /tmp/sglang-metrics, concurrent writes can corrupt the jsonl file of the metrics.Example of corrupted jsonl file with 32 concurrent requests:
Write lock mechanism will prevent this from happening.
Modifications
Added
RWLockfor theFileRequestMetricsExporter, which is acquired when we open the metrics file in_write_record.Accuracy Tests
Not expected to impact model output/accuracy.
Benchmarking and Profiling
Not expected to impact latency/throughput.
Checklist
Review Process
/tag-run-ci-label,/rerun-failed-ci,/tag-and-rerun-ci