Currently Make panics when passed a linker-allocated object. This is
inconsistent with both runtime.AddCleanup and runtime.SetFinalizer. Not
panicking in this case is important so that all pointers can be treated
equally by these APIs. Libraries should not have to worry where a
pointer came from to still make weak pointers.
Supporting this behavior is a bit complex for weak pointers versus
finalizers and cleanups. For the latter two, it means a function is
never called, so we can just drop everything on the floor. For weak
pointers, we still need to produce pointers that compare as per the API.
To do this, copy the tiny lock-free trace map implementation and use it
to store weak handles for "immortal" objects. These paths in the
runtime should be rare, so it's OK if it's not incredibly fast, but we
should keep the memory footprint relatively low (at least not have it be
any worse than specials), so this change tweaks the map implementation a
little bit to ensure that's the case.
Fixes #71726.
Change-Id: I0c87c9d90656d81659ac8d70f511773d0093ce27
Reviewed-on: https://go-review.googlesource.com/c/go/+/649460 Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>