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>
Adds the eventbus to the router subsystem.
The event is currently only used on linux.
Also includes facilities to inject events into the bus.
Updates #15160
Signed-off-by: Claus Lensbøl <claus@tailscale.com>
eventbus.Publish() calls newPublisher(), which in turn invokes (*Client).addPublisher().
That method adds the new publisher to c.pub, so we don’t need to add it again in eventbus.Publish.
Updates #cleanup
Signed-off-by: Nick Khyl <nickk@tailscale.com>
This lets debug tools list the types that clients are wielding, so
that they can build a dataflow graph and other debugging views.
Updates #15160
Signed-off-by: David Anderson <dave@tailscale.com>
If any debugging hook might see an event, Publisher.ShouldPublish should
tell its caller to publish even if there are no ordinary subscribers.
Updates #15160
Signed-off-by: David Anderson <dave@tailscale.com>
Enables monitoring events as they flow, listing bus clients, and
snapshotting internal queues to troubleshoot stalls.
Updates #15160
Signed-off-by: David Anderson <dave@tailscale.com>
The Client carries both publishers and subscribers for a single
actor. This makes the APIs for publish and subscribe look more
similar, and this structure is a better fit for upcoming debug
facilities.
Updates #15160
Signed-off-by: David Anderson <dave@tailscale.com>
