go garbage collector closing reused fds

fd.go

package main

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

func finalizer(f *os.File) {
	fmt.Println("garbage collecting os.File(fd1) created in reuseFd")
}

func reuseFd(fd uintptr) {
	fmt.Println("calling NewFile on fd1")
	f := os.NewFile(fd, "reuse")
	go func() {
		time.Sleep(50 * time.Millisecond)
		runtime.SetFinalizer(f, finalizer)
	}()
}

func main() {
	f, err := os.Open("/dev/zero")
	if err != nil {
		panic(err)
	}
	fd1 := f.Fd()

	reuseFd(fd1)

	f.Close()
	fmt.Println("closed fd1")

	f, err = os.Open("/dev/zero")
	if err != nil {
		panic(err)
	}
	fd2 := f.Fd()
	if fd1 != fd2 {
		panic("failed to reuse same fd")
	}
	success := 0
	for {
		b := make([]byte, 16)
		_, err = f.Read(b)
		if err != nil {
			fmt.Printf("read error: %v\n", err)
			fmt.Printf("success count: %d\n", success)
			return
		}
		success++
		runtime.GC()
		time.Sleep(100 * time.Microsecond)
	}
}