Imagine you are running a web server. It creates a new thread to handle each request. The thread processes the request, sends the response, and terminates. Simple enough.

Now imagine 10,000 users hitting your server simultaneously. That's 10,000 threads. Each thread consumes about 1MB of stack memory, so you're looking at 10GB just for thread stacks.

The operating system is now spending more time switching between threads than actually running your code.

This is a common problem in concurrent systems. Thread creation is expensive, context switching has overhead, and unlimited threads exhaust system resources.

The Thread Pool Pattern solves this by reusing a fixed set of threads to execute many tasks. Instead of creating a new thread for every task, tasks are submitted to a pool where idle workers pick them up.

1. What is the Thread Pool Pattern?