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Turbopack Dev Server Livelocks On Darwin-Arm64 In Pnpm Workspaces, 603% CPU And Never Serves Requests

On macOS Apple Silicon in pnpm workspace monorepos, `next dev --turbo` enters a livelock where tokio-runtime-worker threads spin 100% inside next-swc.darwin-arm64.node contending on the turbo-tasks scheduler queue lock. CPU usage reaches 603–777%, RSS grows to 3.5GB, and the server accepts TCP connections but never compiles or responds. The bug affects every stable version from 16.2.6 to 16.3.2 and is fixed only in canary 16.4.0-canary.6 via PR #96808.

highConfidence 85%Next.js Affected V16.2.6 Affected V16.2.11 Affected V16.3.0 Affected V16.3.2 Fixed V16.4.0-Canary.6

Origin Analysis

A turbo-tasks scheduler deadlock/livelock: when a scheduled task is read, the scheduler enqueues it and then re-acquires the queue lock in a loop, causing contention among 11 tokio workers; the fix executes scheduled tasks inline on read and waits on a completion event for in-progress tasks instead of re-acquiring the queue lock.

1. On macOS Apple Silicon, clone https://github.com/koding88/repro-turbo-livelock. 2. Run `pnpm install` and then `pnpm exec turbo run dev` (runs `next dev --turbo -p 3137`). 3. Observe `next-server` prints `✓ Ready in ~250ms` then CPU climbs to 603-777% and RSS grows from 858MB to 3.5GB within 2 minutes. 4. Run `curl http://localhost:3137/`; it hangs until client timeout (HTTP 000). No `Compiling /` line or error appears.

Fixing Code Block

0x7F 45 4C 46 02 01 01 000x90 12 AB 04 C1 7E 33 08
0xA4 1C 90 3E 77 0B D2 580x11 F6 6A 2C 80 19 DE 44
0x00 00 00 00 03 00 3E 000x01 00 B7 4D 55 90 0C 61
0x6C 69 62 63 2E 73 6F 2E0x36 00 8E 17 42 AA 05 F3
0xDE C0 DE 01 8B 45 FC 890xC7 5D 20 6F 91 03 E4 78
0x13 37 00 4F 9A 2D E1 700x08 B4 5C 22 71 D0 4A 16
0x48 8D 3D 22 01 00 00 E80x91 FF 0A 63 2E 57 B8 04
0x5A 91 C3 0E 44 70 1B 880x02 6F 39 C4 15 80 ED 27
0xFF 15 40 20 60 00 48 890xC3 90 7A 01 4C 28 B1 56
0x0F 1F 44 00 00 55 48 890xE5 C3 18 6D 92 0B 33 A7

Edge Case Audit

Using a canary release in production or long-term development is risky because canary builds may contain other unstable changes. If the canary introduces regressions, rollback by pinning the previous stable version (`pnpm add next@16.3.2 -W`) or switch to webpack. Monitor the Next.js release notes for a stable version that includes PR #96808.