On-callMediumoc-g639

Subject Worker thread pool exhaustionLevel Mid–Senior~30 minCommon in Concurrency · Algorithms & data structures interviewsIndustries Technology, Software development

Question

An image-processing pipeline (a pool of 64 worker threads pulling jobs off a queue) grinds to a halt: the queue backlog grows by tens of thousands, but completed-jobs-per-minute drops to near zero. Dashboards: all 64 workers show 'busy' but throughput is ~0; CPU is low. A thread sample shows most workers stuck inside the same library call decoding a particular video container with no timeout. A user started uploading a batch of malformed/huge files an hour ago. Triage and stabilize the pipeline.

What a strong answer looks like

Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.

Learn the concepts

Diagram & narrate the incident

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Run or narrate your approach, then ask the coach.