espp/thread_pool

# Thread Pool Component [![Badge](https://components.espressif.com/components/espp/thread_pool/badge.svg)](https://components.espressif.com/components/espp/thread_pool) The `ThreadPool` component provides a reusable pool of worker tasks for executing queued jobs asynchronously. It is implemented with `espp::Task` workers and `std::condition_variable` synchronization. ## Features - Configurable worker count - Bounded or unbounded queue - Optional blocking submit mode for backpressure - Manual `start()` / `stop()` control; `start()` returns `true` if all workers launched successfully (or the pool was already running), `false` if any worker failed to start and the pool was rolled back to stopped state - Graceful stop (stops workers; queued jobs may not be executed) - Thread-safe stats for submitted / executed / rejected jobs (total and per band) - **Priority bands** (`espp::QosBand`: `Critical` / `High` / `Normal` / `Low`): `submit(job, band)` / `try_submit(job, band)` enqueue into one FIFO queue per band and workers always pop the most urgent non-empty band first. The band-less `submit(job)` overload uses `Normal`, so existing code is unaffected. - **Aging (anti-starvation)**: a queued job whose wait exceeds `Config::aging_threshold` (default 100 ms) is promoted up one band (to the back of the next band's queue), so a busy high band cannot starve lower bands indefinitely. Set to 0 for strict band priority. - **Per-band workers** (opt-in via `Config::band_worker_counts`): band *k* gets its own workers at `Config::band_task_priorities[k]`, each servicing bands 0..k (its own band and every more urgent band). The deepest (least urgent) configured band's workers service *every* band, so no band is ever unreachable — even with aging disabled. On ESP the priorities are FreeRTOS task priorities and are always applied; on host platforms (Linux/macOS) they map to `SCHED_FIFO` real-time priorities but are **only applied when `Config::band_workers_realtime` is set** — by default the workers run at the OS default scheduling and band ordering is enforced at the queue level only. `SCHED_FIFO` on Linux requires `CAP_SYS_NICE` or an `RLIMIT_RTPRIO` allowance (and a spinning job can starve the system — see the `Config` docs); without permission the workers fall back gracefully to default scheduling with a one-time warning.

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