fix(wasm): eliminate UI hang during prompt prefill#30
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The browser froze for 5-15s after pressing Enter because the prefill loop (running all prompt tokens through 28 layers) had no yield points. ASYNCIFY sleep only fired during token generation, not prefill. Two fixes: 1. quant.h: add emscripten_sleep(0) every 2 tokens in the prefill loop. Browser can repaint and stays responsive. Only active on __EMSCRIPTEN__ builds — native is unaffected. 2. index.html: double-requestAnimationFrame before WASM call ensures "Thinking..." indicator paints before any blocking starts. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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The emscripten_sleep(0) added to quant.h's prefill loop (PR #30) broke ASYNCIFY for the entire quant_generate call. The call stack during tq_forward() is too deep (matmul → SIMD kernels) for ASYNCIFY to unwind/rewind — it silently fails and the generation callback's sleep stops working too. Fix: remove prefill sleep entirely. The prefill blocks the browser for a few seconds (unavoidable without a step-by-step API), but "Thinking..." is shown before via requestAnimationFrame. Token streaming during generation works again. Also: pthreads removed (PR #32) to avoid pthreads+ASYNCIFY conflict, build.sh now uses single-thread SIMD + ASYNCIFY only. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
unamedkr
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Apr 10, 2026
) The emscripten_sleep(0) added to quant.h's prefill loop (PR #30) broke ASYNCIFY for the entire quant_generate call. The call stack during tq_forward() is too deep (matmul → SIMD kernels) for ASYNCIFY to unwind/rewind — it silently fails and the generation callback's sleep stops working too. Fix: remove prefill sleep entirely. The prefill blocks the browser for a few seconds (unavoidable without a step-by-step API), but "Thinking..." is shown before via requestAnimationFrame. Token streaming during generation works again. Also: pthreads removed (PR #32) to avoid pthreads+ASYNCIFY conflict, build.sh now uses single-thread SIMD + ASYNCIFY only. Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Problem
Browser freezes 5-15s after pressing Enter. "Thinking..." indicator never shows because the prefill loop blocks the main thread before the browser can paint.
Root cause
The prefill loop (
quant.h:15465) runstq_forward()for each prompt token with zero yield points. ASYNCIFYemscripten_sleep(0)only existed in the token generation callback, not during prefill.Fix
quant.h:emscripten_sleep(0)every 2 tokens during prefill (guarded by__EMSCRIPTEN__— native unaffected)index.html: doublerequestAnimationFramebefore WASM call guarantees "Thinking..." paints first🤖 Generated with Claude Code