Commits on Sep 17, 2021

1. Fix waker behavior when invoked before a poll finishes …

   It's possible for a task's waker to be invoked in the middle of a call
   to that task's `poll` by the executor. We had accounted for that
   possibility if the task called *its own* waker, but that's not good
   enough: the waker can escape to other threads that can invoke it before
   `poll` finishes (e.g., if the task blocks to acquire a lock).
   
   This change fixes the waker behavior by clarifying the semantics of a
   call to `wake`: a task whose waker is invoked should not be blocked
   *when it next returns Pending to the executor*, and should be woken if
   that has already happened. To do this, we introduce a new `Sleeping`
   state for tasks, that has the same semantics as `Blocked` but that is
   recognized by waker invocations, which will only unblock a task in
   `Sleeping` state. This also removes the special case "woken by self"
   behavior -- being woken by *any* thread should be enough to trigger this
   sleep logic.

   

   jamesbornholt committed Sep 17, 2021
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