Thread Pool / Parallel Task Executor

Problem Implement a fixed-size thread pool that executes submitted tasks using a bounded set of worker threads, with graceful shutdown.

Requirements

• submit(task) enqueues work for execution.
• shutdown() stops accepting new tasks and drains the queue before exiting.
• A pool of K workers processes a stream of N tasks.

Areas to design

• The task queue and how idle workers block on it without busy-waiting.
• Coordinating shutdown so no task is lost and no worker deadlocks.
• Race conditions on the shared queue and the shutdown flag.

Example

• Submit N tasks to a pool of K workers; await completion, then shut down cleanly.