perf(async): remove unused sequence array and eliminate string copies by kcenon · Pull Request #535 · kcenon/logger_system

kcenon · 2026-03-20T01:44:16Z

What

Two performance improvements in the async logging pipeline:

Remove unused sequence_ array from lockfree_spsc_queue (redundant with cells_[i].sequence)
Eliminate unnecessary string copies in high_performance_async_writer hot path

Change Type

Feature (performance optimization)

Affected Components

src/impl/async/lockfree_queue.h — Remove redundant sequence_ array
src/impl/async/high_performance_async_writer.cpp — Construct batch_entry directly with rvalues

Why

The sequence_ array was a separate std::array<std::atomic<size_t>, Size> that duplicated the per-cell sequence field already present in the cell struct — wasting cache lines
The async writer was creating temporary std::string variables for file, function names before passing to batch_entry constructor — unnecessary copies in a hot path

Closes #533
Closes #532

How

Implementation

lockfree_queue.h: Removed alignas(cache_line_size) std::array<std::atomic<size_t>, Size> sequence_ and updated initialization loop to use cells_[i].sequence instead
high_performance_async_writer.cpp: Eliminated intermediate std::string variables; pass to_string() rvalues directly to batch_entry constructor for move semantics

Testing

Initialization loop still correctly sets sequence numbers for ABA prevention
batch_entry construction semantics unchanged (values moved, not copied)

The separate sequence_ array was redundant because each cell already contains its own atomic sequence number (cell::sequence) which is used by enqueue_impl() and dequeue(). The standalone array was initialized in the constructor but never read afterward, wasting Size * sizeof(std::atomic<size_t>) bytes per queue instance. Update the constructor to initialize cells_[i].sequence directly instead of the removed array. Closes #533

Pass to_string() rvalues directly to batch_entry constructor instead of storing them in intermediate local variables. The batch_entry constructor already accepts std::string by value and moves internally, so passing temporaries directly enables move semantics and avoids extra copies on each write() call. Closes #532

Add Performance entries to [Unreleased] section for unused sequence array removal and string copy elimination in hot path.

kcenon · 2026-03-20T04:00:26Z

CI/CD Failure Analysis

Analysis Time: 2026-03-20 11:00 KST
Attempt: #1

Failed Workflows

Workflow	Job	Root Cause	Category
CI	Core-Only Build (macos-14)	`std::format` check fails — Homebrew LLVM Clang 15.0.7 resolved instead of Apple Clang	Environment
CI	macos-14 / clang	Same as above	Environment
Code Coverage	Coverage Analysis	Ubuntu PPA (`ppa.launchpadcontent.net`) network timeout	Transient
Integration Tests	FetchContent Pilot (Ubuntu/gcc/Debug)	Same PPA timeout	Transient
Performance Regression	Performance Regression Check	Same PPA timeout → `gcc-13` not found	Transient

Root Cause Analysis

macOS std::format failure (2 jobs):

The CI workflow uses clang/clang++ without explicit paths. On the previous main branch run (2026-03-19), this resolved to Apple Clang 15.0.0.15000309 which supports std::format. On this PR run (2026-03-20), it resolves to Homebrew LLVM Clang 15.0.7 which does NOT support std::format.

The macos-14 runner image appears to have been updated, changing the PATH resolution order for clang++.

Main (pass): AppleClang 15.0.0.15000309 → HAS_STD_FORMAT: Success
PR   (fail): Clang 15.0.7 (Homebrew)    → HAS_STD_FORMAT: Failed

Ubuntu PPA timeout (3 jobs):

Workflows on ubuntu-22.04 depend on ppa:ubuntu-toolchain-r/test to install gcc-13. The PPA server was unreachable during the CI run, causing apt-get update to fail with exit code 100.

Proposed Fix

Issue	Proposed Solution	Files Affected
macOS compiler path	Use explicit `/usr/bin/clang` and `/usr/bin/clang++` on macOS to ensure Apple Clang is used	`.github/workflows/ci.yml`
Ubuntu PPA timeout	Transient — will be resolved by re-run after push	N/A

Next Steps

Apply macOS compiler path fix
Push and monitor CI
Verify Ubuntu PPA jobs pass on re-run

Automated failure analysis - Attempt #1

The macos-14 runner image updated and clang++ now resolves to Homebrew LLVM Clang 15.0.7 instead of Apple Clang 15.0.0, which lacks std::format support. Use /usr/bin/clang(++) to ensure the system Apple Clang is used.

github-actions · 2026-03-20T04:16:55Z

Performance Regression Check

Benchmark	Base (ns)	PR (ns)	Delta
BM_AsyncDecorator	194.1	191.2	-1.5%
BM_BufferedAsyncDecorator	125.6	118.3	🚀 -5.8%
BM_BufferedDecorator	904.7	917.8	+1.4%
BM_ConsoleAsyncDecorator	286.3	383.0	⚠️ +33.8%
BM_DirectConsoleWriter	5653.0	5880.6	+4.0%
BM_DirectFileWriter	774.5	783.0	+1.1%
BM_ManualNesting_Async	199.1	179.9	🚀 -9.6%
BM_ManualNesting_BufferedAsync	116.9	118.9	+1.7%
BM_ObjectPool_HighContention/real_time/threads:4	1014.7	1024.9	+1.0%
BM_ObjectPool_HighContention/real_time/threads:8	1168.5	1162.4	-0.5%
BM_ObjectPool_MultiThread/real_time/threads:1	18.6	18.6	+0.2%
BM_ObjectPool_MultiThread/real_time/threads:2	123.3	122.6	-0.6%
BM_ObjectPool_MultiThread/real_time/threads:4	103.3	103.5	+0.2%
BM_ObjectPool_MultiThread/real_time/threads:8	117.5	124.0	⚠️ +5.5%
BM_ObjectPool_SingleThread	18.0	18.1	+0.3%
BM_ThreadLocalObjectPool_CacheEfficiency/16/real_time/threads:4	1.3	1.3	+0.1%
BM_ThreadLocalObjectPool_CacheEfficiency/32/real_time/threads:4	1.3	1.3	+0.0%
BM_ThreadLocalObjectPool_CacheEfficiency/4/real_time/threads:4	1.3	1.3	+0.1%
BM_ThreadLocalObjectPool_CacheEfficiency/64/real_time/threads:4	1.3	1.3	-0.0%
BM_ThreadLocalObjectPool_CacheEfficiency/8/real_time/threads:4	1.3	1.4	+0.8%
BM_ThreadLocalObjectPool_HighContention/real_time/threads:4	192.7	194.8	+1.1%
BM_ThreadLocalObjectPool_HighContention/real_time/threads:8	183.7	189.7	+3.3%
BM_ThreadLocalObjectPool_MultiThread/real_time/threads:1	3.7	3.7	+0.2%
BM_ThreadLocalObjectPool_MultiThread/real_time/threads:2	14.7	14.6	-0.7%
BM_ThreadLocalObjectPool_MultiThread/real_time/threads:4	18.7	18.7	-0.1%
BM_ThreadLocalObjectPool_MultiThread/real_time/threads:8	17.5	17.6	+0.6%
BM_ThreadLocalObjectPool_SingleThread	2.8	2.8	-0.0%
BM_Throughput_LargeMessages	188.2	169.5	🚀 -9.9%
BM_Throughput_SmallMessages	192.3	171.7	🚀 -10.7%

Threshold: >5% regression triggers warning
Result: ⚠️ 2 benchmark(s) show potential regression

…#535) * perf(lockfree): remove unused sequence_ array from lockfree_spsc_queue The separate sequence_ array was redundant because each cell already contains its own atomic sequence number (cell::sequence) which is used by enqueue_impl() and dequeue(). The standalone array was initialized in the constructor but never read afterward, wasting Size * sizeof(std::atomic<size_t>) bytes per queue instance. Update the constructor to initialize cells_[i].sequence directly instead of the removed array. Closes #533 * perf(async): eliminate string copies in async writer hot path Pass to_string() rvalues directly to batch_entry constructor instead of storing them in intermediate local variables. The batch_entry constructor already accepts std::string by value and moves internally, so passing temporaries directly enables move semantics and avoids extra copies on each write() call. Closes #532 * docs: update CHANGELOG for #532, #533 Add Performance entries to [Unreleased] section for unused sequence array removal and string copy elimination in hot path. * fix(ci): use explicit Apple Clang path on macOS runners The macos-14 runner image updated and clang++ now resolves to Homebrew LLVM Clang 15.0.7 instead of Apple Clang 15.0.0, which lacks std::format support. Use /usr/bin/clang(++) to ensure the system Apple Clang is used.

kcenon added 3 commits March 20, 2026 10:36

docs: update CHANGELOG for #532, #533

fdb5426

Add Performance entries to [Unreleased] section for unused sequence array removal and string copy elimination in hot path.

kcenon added performance Performance improvements priority:high High priority issue core Core functionality labels Mar 20, 2026

fix(ci): use explicit Apple Clang path on macOS runners

b51acfb

The macos-14 runner image updated and clang++ now resolves to Homebrew LLVM Clang 15.0.7 instead of Apple Clang 15.0.0, which lacks std::format support. Use /usr/bin/clang(++) to ensure the system Apple Clang is used.

kcenon merged commit 7a06725 into main Mar 20, 2026
33 checks passed

kcenon deleted the perf/533-remove-unused-sequence branch March 20, 2026 04:21

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perf(async): remove unused sequence array and eliminate string copies#535

perf(async): remove unused sequence array and eliminate string copies#535
kcenon merged 4 commits into
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perf/533-remove-unused-sequence

kcenon commented Mar 20, 2026

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kcenon commented Mar 20, 2026

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kcenon commented Mar 20, 2026

What

Change Type

Affected Components

Why

How

Implementation

Testing

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kcenon commented Mar 20, 2026

CI/CD Failure Analysis

Failed Workflows

Root Cause Analysis

Proposed Fix

Next Steps

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github-actions Bot commented Mar 20, 2026

Performance Regression Check

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