Node.js worker threads are problematic, but they work great for us

Node.js operates on a single-threaded model, which is generally efficient for handling I/O concurrency through its event loop, but can lead to problems when CPU-intensive tasks monopolize the main thread, causing event loop starvation. This issue was encountered with Inngest Connect, a persistent WebSocket connection that experienced "no available worker" errors due to CPU-heavy user code blocking heartbeats. The solution involved shifting Connect internals to a worker thread, enabling isolation of critical path operations from user workloads. Worker threads in Node.js, unlike concurrency primitives in other languages, require communication through message passing, as they can't directly execute functions passed to them. Each worker, being a separate V8 isolate, communicates with the main thread via serialized messages, which, while adding overhead, ensures independent event loops. This approach resolved the starvation problem but required careful handling of communication protocols and management of worker thread lifecycle, including respawning with exponential backoff to handle potential worker crashes. Despite these challenges, the use of worker threads effectively eliminated the errors and maintained robust WebSocket connections, demonstrating their value in scenarios where main thread yield cannot be guaranteed.

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