Prepare the futex-based implementation of lock2 to maintain a list of
waiting Ms. Beyond storing an muintptr in the mutex's key field, we now
must never overwrite that field (even for a moment) without taking its
current value into account.
The semaphore-based implementation of lock2 already has that behavior.
Reuse that structure.
For #66999
Change-Id: I23b6f6bacb276fe33c6aed5c0571161a7e71fe6c
Reviewed-on: https://go-review.googlesource.com/c/go/+/585636 Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Rhys Hiltner <rhys.hiltner@gmail.com> Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>