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Serialize production frontend work sharing one .web directory - #7453
FarhanAliRaza wants to merge 3 commits into
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Two exports (or an export and a prod/preview start) in the same project used to race on .web: the second replaced build/ and env.json while the first was still compiling or zipping, so one of them shipped the other's frontend. Hold an exclusive, reentrant file lock on .web/.reflex-build.lock from compilation through ZIP creation, release it before serving, and never create .web for a backend-only export that has nothing to protect. Split out of #7054 (lock only; the opt-in build cache that needs it follows separately). Claude-Session: https://claude.ai/code/session_018nWB9r2HcC5tkT72UxWgGj
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💡 Codex ReviewLine 69 in b7d35ca  Lock backend exports before checking for .web
When a backend-only export starts while ℹ️ About Codex in GitHubYour team has set up Codex to review pull requests in this repo. Reviews are triggered when you
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Merging this PR will improve performance by 5.73%
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| Benchmark | BASE |
HEAD |
Efficiency | |
|---|---|---|---|---|
| ⚡ | test_route_argument_extraction |
121.4 µs | 113.4 µs | +7.11% |
| ⚡ | test_from_event_type[event_spec] |
97.3 µs | 93.2 µs | +4.37% |
Tip
Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.
Comparing farhan/frontend-workspace-lock (a639b01) with main (d2528ac)
Footnotes
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18 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩
Brings in #7449, which drops Python 3.10 and moves ruff to py311. Claude-Session: https://claude.ai/code/session_01PXcFKAgnzhgdnSvhuCmxWE
PERF203 only applies before Python 3.11, where try/except in a loop costs per iteration. With ruff targeting py311 since #7449 the directive is unused, which RUF100 rejects. Claude-Session: https://claude.ai/code/session_01PXcFKAgnzhgdnSvhuCmxWE
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should consolidate locking implementation with existing json_file_lock so we don't have multiple code paths handling platform-specific file locking in slightly different ways
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Split out of #7054. This is the lock only; the opt-in build cache that motivated it is #7455 and is stacked on this.
Problem
Two production exports in the same project (or an export racing a
reflex run --env prodstart) share.web: the second one rewritesenv.json,build/, and the compiled sources while the first is still compiling or zipping, so one of them ships the other's frontend. Review bots on #7054 flagged this for the cache, but it is a pre-existing race.Changes
reflex/utils/build_lock.py: an exclusive, reentrant, per-.webfile lock on.web/.reflex-build.lock(flockon POSIX,msvcrt.lockingwith a 100 ms poll on Windows). Nested calls in one thread reuse the lock; forked children drop inherited ownership; a symlinked or non-regular lock path is refused instead of silently proceeding unlocked.export.export()holds it from configuration through ZIP creation. A backend-only export takes it only when.webalready exists (it archives.web/backend), and never creates.web._run_prod/_run_previewhold it through compile and build and release it before serving.Measurement
No speedup is claimed. Lock overhead on an unchanged bun export, repeat runs:
This is pure complexity in service of correctness (and of #7455). If the cache is not wanted, the question for this one is only whether the race above is worth fixing.
Measurement setup
Five-page app from the
blanktemplate (Radix Themes + Tailwind v4 plugins), Linux x86_64, 4 vCPU, Python 3.14, Node 22.22, npm 10.9, bun 1.4.2. Each run is a fresh interpreter callingreflex.utils.export.export()the same wayreflex exportdoes; durations are the phase timings the export already reports to telemetry (compileincludes the dependency install). Medians of 3 runs unless noted. Vite dominates every export (~6.5 s); these numbers isolate the part this PR touches.Type of change
Checklist
tests/unitssuite passes locally except the 14reflex_bench/drivers/test_browser.pycases that need a Playwright browser launch, which fail identically on untouchedmainin this sandboxruff check,ruff format --check,codespell, andpyright reflex testspass locallyhttps://claude.ai/code/session_018nWB9r2HcC5tkT72UxWgGj