runtime: SetFinalizer doesn't work on pointers to empty structs

[bradfitz]

runtime.SetFinalizer crashes at runtime if you register a finalizer on an empty struct.

package main

import "runtime"

type T struct{ i int }
type TE struct{}

func main() {
        t := new(T)
        te := new(TE)
        runtime.SetFinalizer(t, func(*T) {})
        runtime.SetFinalizer(te, func(*TE) {}) // runtime crash
}

With:

runtime.SetFinalizer: pointer not at beginning of allocated block
fatal error: runtime.SetFinalizer


Go tip (basically Go 1.2)

[rsc]

Comment 1:

Too bad I guess. Zero-size values are not allocations - they all return the same
pointer, which is not part of the standard heap. Setting a finalizer on that would not
be useful, since it is never freed.
We aren't going to remove this optimization, so either we should make SetFinalizer just
be a no-op in this case or document that it is invalid to use SetFinalizer on blocks of
size zero.

Labels changed: added go1.3, documentation, removed go1.3maybe.

[rsc]

Comment 2:

Labels changed: added release-go1.3.

[rsc]

Comment 3:

Labels changed: removed go1.3.

[rsc]

Comment 4:

Labels changed: added repo-main.

[bradfitz]

Comment 5:

Sent https://golang.org/cl/43580043

Status changed to Started.

[bradfitz]

Comment 6:

This issue was closed by revision 4b76a31.

Status changed to Fixed.