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v1.5.5 — warm-path perf fix: ensure_emscripten_available 940ms → ~1ms

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@zackees zackees released this 19 May 10:15
· 15 commits to main since this release
v1.5.5
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Warm-path performance fix for ensure_emscripten_available(). The function was costing ~940 ms per call in FastLED's bash compile wasm warm-rebuild timing, dominated by two HTTPS calls to GitHub verifying the upstream SHA256 hadn't changed.

Bench (Windows, fresh install)

Path Before (1.5.4) After (1.5.5)
Warm: done.txt < 24h + marker present ~940 ms ~1 ms
Memoized: second call same process ~940 ms ~0.001 ms
Forced re-check (CLANG_TOOL_CHAIN_FORCE_MANIFEST_CHECK=1) ~940 ms ~210 ms
Cold (no done.txt) — unchanged

What changed (four layered fast paths)

1. Skip GitHub manifest re-fetch when done.txt is fresh

is_emscripten_installed() makes 2 HTTPS calls every invocation to verify upstream SHA256. New _can_skip_manifest_recheck(done_path) short-circuits when done.txt is < 24 h old. Override with CLANG_TOOL_CHAIN_FORCE_MANIFEST_CHECK=1 for explicit re-check. clang-tool-chain install ... still always hits the network.

2. Marker file in _apply_wasm_ld_patch

First successful patch drops .ctc-wasm-ld-patched.v1 sidecar. Subsequent calls take one Path.exists() instead of reading ~30 MB shared.py and substring-scanning for the inline marker. Pre-1.5.5 installs detect-and-upgrade on first call.

3. Process-level memoization

set[(platform, arch)] of verified tuples. Second call in same process is a no-op. Cross-process callers (FastLED's per-build subprocess pattern) get the marker + done.txt-age paths instead.

4. Skip _verify_file_readable past 5 s race window

Three open()+read() checks that guarded a Windows filesystem-sync race in the first seconds after extraction. Once done.txt is older than 5 s the race is closed; skip. Saves ~30–100 ms.

Compatibility

  • No API changes
  • Backwards-compatible with pre-1.5.5 patched installs (auto-upgrades the marker on first call)
  • Reinstalls wipe install_dir wholesale, so marker + shared.py stay coherent
  • Memoization is per-process; cross-process behaviour unchanged
  • New env var CLANG_TOOL_CHAIN_FORCE_MANIFEST_CHECK=1 for explicit re-checks

Tests

10 new unit tests + 84 broader emscripten regression tests pass. Pyright + ruff clean.

Install

pip install --upgrade clang-tool-chain

🤖 Generated with Claude Code

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