package main

import "runtime"

func main() {
    {
        x := inuse()
        c := make(chan []byte, 10)
        c <- make([]byte, 10<<20)
        close(c)
        f1(c, x)
    }
    {
        x := inuse()
        c := make(chan []byte, 10)
        c <- make([]byte, 10<<20)
        close(c)
        f2(c, x)
    }
}

func f1(c chan []byte, start int64) {
    for x := range c {
        if delta := inuse() - start; delta < 9<<20 {
            println("f1: after alloc: expected delta at least 9MB, got: ", delta)
        }
        println(x)
        x = nil
        if delta := inuse() - start; delta > 1<<20 {
            println("f1: after alloc: expected delta below 1MB, got: ", delta)
        }
        println(x)
    }
}

func f2(c chan []byte, start int64) {
    for {
        x, ok := <-c
        if !ok {
            break
        }
        if delta := inuse() - start; delta < 9<<20 {
            println("f2: after alloc: expected delta at least 9MB, got: ", delta)
        }
        println(x)
        x = nil
        if delta := inuse() - start; delta > 1<<20 {
            println("f2: after alloc: expected delta below 1MB, got: ", delta)
        }
        println(x)
    }
}

func inuse() int64 {
    runtime.GC()
    var st runtime.MemStats
    runtime.ReadMemStats(&st)
    return int64(st.Alloc)
}