Reduce peak memory in getFileHashes

[hamidrezahanafi]

Summary

Reduce peak memory in getFileHashes by pooling read buffers instead of one buffer per file.

Storybook builds with many static assets caused Chromatic CLI to pre-allocate a 64KiB buffer per file before hashing, so memory scaled as O(files × 64KiB) and could push CI containers over their limit. This change reuses a small buffer pool sized to min(concurrency, file count), so allocation is O(concurrency × 64KiB) while preserving the same hashing behavior.

Changes

• Replace per-file Buffer.allocUnsafe(64 * 1024) upfront with acquire/release from a fixed pool tied to p-limit concurrency.
• Clamp invalid / out-of-range CHROMATIC_HASH_CONCURRENCY to a safe range and handle files.length === 0 without doing work.
• Tests: golden hash snapshot; empty list; spy asserting pool-sized allocUnsafe calls; equality of hashes for concurrency: 1 vs higher concurrency, including one file > 64KiB to exercise incremental reads under pooling.

Benchmark (local, 3000 small files, concurrency 8, NODE_OPTIONS=--expose-gc)

Measured with process.memoryUsage() before/after a full hash pass; legacy implementation duplicated the pre-pool “one buffer per file” strategy for comparison.

Variant	Δ arrayBuffers	Δ external	Δ heapUsed
Legacy (buffer per file)	+183.2 MiB	+187.5 MiB	+0.41 MiB
Pooled (this PR)	~0 MiB	+0.56 MiB	+0.31 MiB

Most of the legacy cost shows up under arrayBuffers / external (Buffer backing memory), not V8 heapUsed. Pooled behavior aligns with 3000 × 64 KiB ≈ 187.5 MiB no longer being held for read buffers at once.

Notes

• Correctness is covered by snapshot expectations and by comparing pooled vs sequential runs on the same files.

[codecov]

Codecov Report

❌ Patch coverage is 87.23404% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.46%. Comparing base (c175ff8) to head (0e42bc5).

Files with missing lines	Patch %	Lines
node-src/lib/getFileHashes.ts	87.23%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1258      +/-   ##
==========================================
+ Coverage   72.22%   72.46%   +0.23%     
==========================================
  Files         208      208              
  Lines        7918     7961      +43     
  Branches     1435     1450      +15     
==========================================
+ Hits         5719     5769      +50     
+ Misses       2177     2170       -7     
  Partials       22       22              

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