// The ring index word is the parking word (L21). Two properties are owed by
// any parking scheme, and both are asserted here:
//
//   - no lost wakeup: a receiver parked on the write index is woken by the
//     publish, so a ping-pong over a spawn channel completes every round;
//   - no hang on peer death: a parent parked on a ring whose child died
//     unpacks (bounded wait, then a liveness recheck) and reports the closed
//     channel rather than sleeping forever.
package main

import (
	"fmt"
	"runtime"
	"time"
)

// echoWorker receives each value and answers with twice it, so the parent can
// tell that the parked receive actually woke. It parks on `in` between
// messages: that park is the wakeup the test is about.
func echoWorker(in chan int32, out chan int32) {
	for {
		v, ok := <-in
		if !ok {
			return
		}
		out <- v * 2
	}
}

// deadWorker returns without ever writing out, so its parent parks on out and
// then has to notice the peer died.
func deadWorker(in chan int32, out chan int32) {
	time.Sleep(50 * time.Millisecond)
}

func main() {
	// Chan memory must outlive this frame: the forked child reads the same
	// channel memory, so allocate it in the root arena.
	runtime.SovereignSetArena(runtime.RootArena())
	in := chan int32{}
	out := chan int32{}
	done := spawn(echoWorker, in, out)

	// 200 rounds: each one parks the worker on `in`, publishes, and requires
	// the reply. If a wake were lost the round would stall until the bounded
	// park timed out and the test would eventually fail on the value.
	for i := int32(0); i < 200; i++ {
		in <- i
		v := <-out
		if v != i*2 {
			panic("echo value mismatch")
		}
	}
	close(in)
	<-done
	fmt.Println("wake ok")

	runtime.SovereignSetArena(runtime.RootArena())
	in2 := chan int32{}
	out2 := chan int32{}
	done2 := spawn(deadWorker, in2, out2)

	start := time.Now()
	dv, ok := <-out2
	elapsed := time.Since(start)
	_ = dv
	if ok {
		panic("recv reported a value after the peer died")
	}
	if elapsed > 3*time.Second {
		panic("recv did not unpark promptly after the peer died")
	}
	<-done2
	fmt.Println("dead ok")
}