1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
|
// run
// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import "runtime"
var finalized bool
var err string
type HeapObj [8]int64
const filler int64 = 0x123456789abcdef0
func (h *HeapObj) init() {
for i := 0; i < len(*h); i++ {
h[i] = filler
}
}
func (h *HeapObj) check() {
for i := 0; i < len(*h); i++ {
if h[i] != filler {
err = "filler overwritten"
}
}
}
type StackObj struct {
h *HeapObj
}
func gc(shouldFinalize bool) {
runtime.GC()
runtime.GC()
runtime.GC()
if shouldFinalize != finalized {
err = "heap object finalized at the wrong time"
}
}
func main() {
var s StackObj
s.h = new(HeapObj)
s.h.init()
runtime.SetFinalizer(s.h, func(h *HeapObj) {
finalized = true
})
gc(false)
h := g(&s)
gc(false)
h.check()
gc(true) // finalize here, after return value's last use. (Go1.11 never runs the finalizer.)
if err != "" {
panic(err)
}
}
func g(p *StackObj) (v *HeapObj) {
gc(false)
v = p.h // last use of the stack object. the only reference to the heap object is in the return slot.
gc(false)
defer func() {
gc(false)
recover()
gc(false)
}()
*(*int)(nil) = 0
return
}
|
