How does java.util.concurrent classes reuse threads?

Question

I'm talking about the Thread instances, if they get their Runnable provided as a constructor argument and you can only execute their start method once, how come the Executor* family of classes reuse them?

PS: I know and use the Executors classes which are nicer abstraction than bare threads, I'm asking this just out of curiosity.

Answer 1

The runnables (lets call them R) passed to executor threads are in fact wrapped inside other runnables (let's call them W). The pseudo-code of the run() method of W is

while (threadMustRun) {
    wait for new R to be submitted and assigned to this thread
    execute R.run()
}

It's actually more complex than that, but you should get the idea. To really understand what it does, look at the code the the ThreadPoolExecutor.Worker inner class.