util/eventbus: add a Done channel to the Client (#17118)

Subscribers already have a Done channel that the caller can use to detect when
the subscriber has been closed. Typically this happens when the governing
Client closes, which in turn is typically because the Bus closed.

But clients and subscribers can stop at other times too, and a caller has no
good way to tell the difference between "this subscriber closed but the rest
are OK" and "the client closed and all these subscribers are finished".

We've worked around this in practice by knowing the closure of one subscriber
implies the fate of the rest, but we can do better: Add a Done method to the
Client that allows us to tell when that has been closed explicitly, after all
the publishers and subscribers associated with that client have been closed.
This allows the caller to be sure that, by the time that occurs, no further
pending events are forthcoming on that client.

Updates #15160

Change-Id: Id601a79ba043365ecdb47dd035f1fdadd984f303
Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>

0 files changed, 0 insertions, 0 deletions