Render concurrency

FIFO semaphore limiting concurrent Puppeteer renders per Node process.

Module: @sumx/ssr-pdf/pdf-render-slot

Why it exists

Each PDF request can spawn Chromium work. Without a cap, traffic spikes create unbounded processes and OOM kills. The slot queue bounds active renders and queues the rest.

API

import { acquirePdfRenderSlot, releasePdfRenderSlot } from '@sumx/ssr-pdf/pdf-render-slot';
 
await acquirePdfRenderSlot();
try {
  // puppeteer render
} finally {
  releasePdfRenderSlot();
}

The API route handler calls these automatically — you rarely invoke them directly unless building a custom pipeline.

Behavior

• Default max concurrent: 2
• Env override: HTML_TO_PDF_MAX_CONCURRENT (1–8, invalid → 2)
• Extra requests wait (FIFO), not rejected
• Per-process only — scale horizontally with multiple replicas for throughput

Tuning

Monitor memory and p95 latency when increasing.

Custom usage

If you add a second PDF entry point, always pair acquire/release in finally to avoid deadlocking the queue.