internal/poll: defer IOCP association until first IO operation
Defer the association of the IOCP to the handle until the first
I/O operation is performed.
A handle can only be associated with one IOCP at a time, so this allows
external code to associate the handle with their own IOCP and still be
able to use a FD (through os.NewFile) to pass the handle around
(e.g. to a child process standard input, output, and error) without
having to worry about the IOCP association.
This CL doesn't change any user-visible behavior, as os.NewFile still
initializes the FD as non-pollable.
For #19098.
Change-Id: Id22a49846d4fda3a66ffcc0bc1b48eb39b395dc5
Reviewed-on: https://go-review.googlesource.com/c/go/+/661955 Reviewed-by: Damien Neil <dneil@google.com> Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>