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⚡ Coalesce concurrent image resize requests#34

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si wants to merge 4 commits intomainfrom
perf/srcset-race-condition-6831872195030513611
Open

⚡ Coalesce concurrent image resize requests#34
si wants to merge 4 commits intomainfrom
perf/srcset-race-condition-6831872195030513611

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@si si commented Feb 17, 2026

💡 What:

  • Implemented request coalescing in _11ty/srcset.js using a module-level Map (inFlight) to track pending image resize operations.
  • Concurrent requests for the same output file now wait for the initial promise instead of starting a new sharp process.
  • Used .finally() on the promise chain to ensure the map entry is removed after the operation completes (success or failure).

🎯 Why:

  • The previous implementation had a race condition: resize checked for file existence, then started sharp. If multiple build tasks requested the same resize concurrently, they would all see the file as missing and trigger redundant sharp processing, wasting CPU and I/O.
  • This optimization significantly reduces the number of sharp invocations during parallel builds (e.g., from 20 calls to 4 calls for 5 concurrent requests of 4 sizes).

📊 Measured Improvement:

  • Verified with a reproduction script (repro_test.js) that simulated 5 concurrent requests for the same image (generating 4 sizes each).
  • Baseline: 20 sharp calls.
  • Optimized: 4 sharp calls (1 per unique size).
  • This represents a 5x reduction in sharp calls for this specific scenario.
  • Existing tests passed (npm test).

PR created automatically by Jules for task 6831872195030513611 started by @si

Prevents race conditions where multiple build tasks trigger redundant
`sharp` image processing for the same file. Uses a `Map` to track
in-flight resize promises and reuse them.

Co-authored-by: si <18108+si@users.noreply.github.com>
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google-labs-jules bot and others added 3 commits February 17, 2026 11:24
Prevents race conditions where multiple build tasks trigger redundant
`sharp` image processing for the same file. Uses a `Map` to track
in-flight resize promises and reuse them.

(Reverted lockfile changes to fix CI build)

Co-authored-by: si <18108+si@users.noreply.github.com>
Prevents race conditions where multiple build tasks trigger redundant
`sharp` image processing for the same file. Uses a `Map` to track
in-flight resize promises and reuse them.

Additionally, lazy-loads `sharp` and `fs` dependencies to ensure
compatibility with Cloudflare Workers build environments that may
bundle this file but not support these native modules at runtime.

Co-authored-by: si <18108+si@users.noreply.github.com>
Prevents race conditions where multiple build tasks trigger redundant
`sharp` image processing for the same file. Uses a `Map` to track
in-flight resize promises and reuse them.

Additionally, uses `eval("require")` for `sharp` and `fs` to bypass
bundler static analysis, fixing Cloudflare Workers build failures.

Co-authored-by: si <18108+si@users.noreply.github.com>
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