In #21031, this can be optimized to reduce the Pointer,usage atomic-operate
for any type, as shown in https://go-review.googlesource.com/c/go/+/617695 .
But we need support for setting atomic values to nil, and we also need a
way to represent deleted values.
The current practice is to make a spin lock using the typ field of any.
I want to ask if we can do better this way:
typ remains unchanged after the first setting,Cases such as being deleted
are represented by a special internal package pointer, which is set to data
field.
An example to illustrate this approach:
```go
package main
import (
"sync/atomic"
"unsafe"
)
var delete byte
func main() {
var v atomic.Value
var i int = 1
v.Store(i)
// Make a any , it is typ=int meta data,data=&byte
nv := new_delete(getIntType())
// Indicates deleted
v.Store(nv)
}
type iface struct {
typ, data unsafe.Pointer
}
func new_delete(typ unsafe.Pointer) any {
ret := iface{
typ: typ,
data: unsafe.Pointer(&delete),
}
return *(*any)(unsafe.Pointer(&ret))
}
func getIntType() unsafe.Pointer {
var i int
var a any = i
var as *iface = (*iface)(unsafe.Pointer(&a))
return as.typ
}
```
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