Brings Subscriber[T] in line with the same non-generic-core pattern already
applied to SubscriberFunc[T] and Publisher[T]:
- Renames subscriberFuncCore to subscriberCore and shares it between
Subscriber[T] and SubscriberFunc[T]. Both typed facades hold a
*subscriberCore plus their respective per-T delivery state
(Subscriber: chan T; SubscriberFunc: nothing, the user callback is
captured in the dispatch closure).
- The bus's outputs map and subscriber-interface itab key on
*subscriberCore for both subscriber kinds, so adding a new Subscribe[T]
call site no longer pays a per-T itab, dictionary, or equality function
for the subscriber-interface side.
- Subscribe[T] now hoists the non-generic constructor portion into
newSubscriberCore (timer setup, core allocation, cached type/typeName,
unregister method-value), matching SubscribeFunc.
The dispatch loop is intentionally NOT extracted to a non-generic helper for
Subscriber[T], unlike SubscriberFunc[T]. The reason is the typed channel send
'case s.read <- t:' must appear lexically inside the select; the only way to
lift it into a non-generic loop is to bridge typed and untyped via a per-event
goroutine, which costs ~2.7x throughput on BenchmarkBasicThroughput. We keep
dispatchTyped on the generic facade and accept the per-shape stencil cost as
the cheaper alternative.
Symbol-level effect on tailscaled (linux/amd64, measured via
`go tool nm -size`):
Before:
(*Subscriber[T]).dispatch
2 shape stencils: 1,682 + 1,549 = 3,231 B
3 thin per-T wrappers: 124 B each = 372 B
2 deferwrap1 helpers: 62 B each = 124 B
total: 3,727 B
After:
(*Subscriber[T]).dispatchTyped
2 shape stencils: 1,678 + 1,582 = 3,260 B
0 per-T wrappers (replaced by closure stored on core)
2 deferwrap1 helpers: 62 B each = 124 B
total: 3,384 B
dispatch path .text delta: -343 B (-9.2%)
Per-shape stencils are ~1,600 B (.text body) + ~1,100 B (pclntab) =
~2,700 B each on production tailscaled. The shape count matches before/after
(two distinct GC shapes for the Subscriber[T] event types in this binary).
What changes is that the per-T thin wrappers are eliminated because
Subscriber[T] no longer implements the subscriber interface directly.
Whole-binary section deltas:
.text: -2,304 B (includes the dispatch savings plus other
small downstream effects)
.rodata: +512 B (additional closure-type metadata)
.gopclntab: -2,981 B (fewer per-T compiled functions => less metadata)
Stripped tailscaled (linux/amd64): no change at the file level (the savings
fall below the linker's section-alignment boundary). Unstripped builds shrink
by ~2,900 B.
Behavior is unchanged:
BenchmarkBasicThroughput: 2,161 ns/op, 0 B/op, 0 allocs/op
BenchmarkBasicFuncThroughput: 2,493 ns/op, 144 B/op, 2 allocs/op
BenchmarkSubsThroughput: 3,727 ns/op, 0 B/op, 0 allocs/op
Updates #12614
Change-Id: I97918ec68bd2cdb15958bbfd7687592b39663efe
Signed-off-by: James Tucker <james@tailscale.com>
Mirrors the same refactor previously applied to SubscriberFunc:
- Publisher[T]: a thin user-facing facade. Holds a pointer to a
non-generic publisherCore and exposes Publish/Close/ShouldPublish.
- publisherCore: a non-generic struct that owns the *Client back-
pointer, stop flag, and cached reflect.Type. It implements the
package-private publisher interface (publishType, Close).
The bus's per-Client publisher set is set.Set[publisher] keyed
on this single non-generic type.
The publisher interface only exists to support diagnostic
introspection (Debugger.PublishTypes returning the list of types a
client publishes). Previously, satisfying that diagnostic-only
interface forced *Publisher[T] to be the implementor and cost a
per-T itab, generic dictionary, and equality function on every
event type ever passed through Publish[T]. Moving the
implementation to a non-generic core lets the diagnostic surface
work unchanged while charging zero per-T cost for the
diagnostic-driven generic interface.
Publisher[T].Publish is also slimmed: the channel/select/stopFlag
loop is now a non-generic publish() helper that takes the value as
'any'. The per-T body is reduced to forwarding the boxed value to
the helper.
Measured impact (util/eventbus/sizetest):
total per-flow binary cost:
linux/amd64: 2252.8 B/flow -> 1900.5 B/flow (-352.3 B / -15.6%)
linux/arm64: 2228.2 B/flow -> 1835.0 B/flow (-393.2 B / -17.6%)
Publisher per-receiver attribution:
linux/amd64: 635.2 B/flow -> 369.6 B/flow (-265.6 B / -41.8%)
linux/arm64: 751.7 B/flow -> 373.2 B/flow (-378.5 B / -50.4%)
Cumulative reduction from the original baseline (5167ff412):
linux/amd64: 3096.6 B/flow -> 1900.5 B/flow (-1196.1 B / -38.6%)
linux/arm64: 3145.7 B/flow -> 1835.0 B/flow (-1310.7 B / -41.7%)
Dropped per-T symbols (200-flow eventbus binary):
- .dict.Publisher[T] was 14,400 B (72 B/T)
- type:.eq.Publisher[T] was 11,832 B (58 B/T)
- go:itab.*Publisher[T],publisher was 8,000 B (40 B/T)
- (*Publisher[T]).Close shape stencils collapsed to 1
Behavior is unchanged: BenchmarkBasicThroughput is within noise
(2018 -> 2038 ns/op at -benchtime=2s) and all eventbus tests pass.
Updates #12614
Change-Id: I61979c2bf95d2a711c2321e6e0b4b7d15980e9f5
Signed-off-by: James Tucker <james@tailscale.com>
Splits SubscriberFunc[T] into:
- SubscriberFunc[T]: a thin user-facing facade that holds only a
pointer to a non-generic core. It exposes Close() to user code,
which forwards to the core.
- subscriberFuncCore: a non-generic struct that owns all the
subscriber state (stop flag, unregister, logf, slow timer,
cached reflect.Type) and implements the bus's package-private
subscriber interface. Its dispatch() invokes a closure
captured at construction time that performs the
vals.Peek().Event.(T) type assertion and runs the user
callback on the unboxed value.
The bus's outputs map and subscriber-interface itab are
parameterized only by *subscriberFuncCore, not by T, eliminating
both the per-T itab and the per-T generic dictionary that
previously scaled with the number of subscribed event types.
Measured impact (util/eventbus/sizetest):
total per-flow binary cost:
linux/amd64: 3039.2 B/flow -> 2252.8 B/flow (-786.4 B / -25.9%)
linux/arm64: 3145.7 B/flow -> 2228.2 B/flow (-917.5 B / -29.2%)
SubscriberFunc per-receiver attribution:
linux/amd64: 840.8 B/flow -> 300.8 B/flow (-540.0 B / -64.2%)
linux/arm64: 849.9 B/flow -> 303.8 B/flow (-546.1 B / -64.3%)
Dropped per-T symbols (200-flow eventbus binary):
- (*SubscriberFunc[T]).dispatch was 26,639 B total (130 B/T)
- (*SubscriberFunc[T]).subscribeType was 3,600 B total ( 18 B/T)
- .dict.SubscriberFunc[T] was 14,400 B total ( 72 B/T)
- go:itab.*SubscriberFunc[T],... was 9,600 B total ( 48 B/T)
Of the original 913 B/flow attributed to SubscriberFunc, 540 B/flow
is now gone, dropping the receiver to 300 B/flow.
Behavior is unchanged: BenchmarkBasicThroughput is within noise
(1955 -> 1941 ns/op on the test box) and all eventbus tests pass.
Updates #12614
Change-Id: I646b3b05fd8d95f9afead59bfd0f69cd18b7a709
Signed-off-by: James Tucker <james@tailscale.com>
This file was never truly necessary and has never actually been used in
the history of Tailscale's open source releases.
A Brief History of AUTHORS files
---
The AUTHORS file was a pattern developed at Google, originally for
Chromium, then adopted by Go and a bunch of other projects. The problem
was that Chromium originally had a copyright line only recognizing
Google as the copyright holder. Because Google (and most open source
projects) do not require copyright assignemnt for contributions, each
contributor maintains their copyright. Some large corporate contributors
then tried to add their own name to the copyright line in the LICENSE
file or in file headers. This quickly becomes unwieldy, and puts a
tremendous burden on anyone building on top of Chromium, since the
license requires that they keep all copyright lines intact.
The compromise was to create an AUTHORS file that would list all of the
copyright holders. The LICENSE file and source file headers would then
include that list by reference, listing the copyright holder as "The
Chromium Authors".
This also become cumbersome to simply keep the file up to date with a
high rate of new contributors. Plus it's not always obvious who the
copyright holder is. Sometimes it is the individual making the
contribution, but many times it may be their employer. There is no way
for the proejct maintainer to know.
Eventually, Google changed their policy to no longer recommend trying to
keep the AUTHORS file up to date proactively, and instead to only add to
it when requested: https://opensource.google/docs/releasing/authors.
They are also clear that:
> Adding contributors to the AUTHORS file is entirely within the
> project's discretion and has no implications for copyright ownership.
It was primarily added to appease a small number of large contributors
that insisted that they be recognized as copyright holders (which was
entirely their right to do). But it's not truly necessary, and not even
the most accurate way of identifying contributors and/or copyright
holders.
In practice, we've never added anyone to our AUTHORS file. It only lists
Tailscale, so it's not really serving any purpose. It also causes
confusion because Tailscalars put the "Tailscale Inc & AUTHORS" header
in other open source repos which don't actually have an AUTHORS file, so
it's ambiguous what that means.
Instead, we just acknowledge that the contributors to Tailscale (whoever
they are) are copyright holders for their individual contributions. We
also have the benefit of using the DCO (developercertificate.org) which
provides some additional certification of their right to make the
contribution.
The source file changes were purely mechanical with:
git ls-files | xargs sed -i -e 's/\(Tailscale Inc &\) AUTHORS/\1 contributors/g'
Updates #cleanup
Change-Id: Ia101a4a3005adb9118051b3416f5a64a4a45987d
Signed-off-by: Will Norris <will@tailscale.com>
Add options to the eventbus.Bus to plumb in a logger.
Route that logger in to the subscriber machinery, and trigger a log message to
it when a subscriber fails to respond to its delivered events for 5s or more.
The log message includes the package, filename, and line number of the call
site that created the subscription.
Add tests that verify this works.
Updates #17680
Change-Id: I0546516476b1e13e6a9cf79f19db2fe55e56c698
Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>
Originally proposed by @bradfitz in #17413.
In practice, a lot of subscribers have only one event type of interest, or a
small number of mostly independent ones. In that case, the overhead of running
and maintaining a goroutine to select on multiple channels winds up being more
noisy than we'd like for the user of the API.
For this common case, add a new SubscriberFunc[T] type that delivers events to
a callback owned by the subscriber, directly on the goroutine belonging to the
client itself. This frees the consumer from the need to maintain their own
goroutine to pull events from the channel, and to watch for closure of the
subscriber.
Before:
s := eventbus.Subscribe[T](eventClient)
go func() {
for {
select {
case <-s.Done():
return
case e := <-s.Events():
doSomethingWith(e)
}
}
}()
// ...
s.Close()
After:
func doSomethingWithT(e T) { ... }
s := eventbus.SubscribeFunc(eventClient, doSomethingWithT)
// ...
s.Close()
Moreover, unless the caller wants to explicitly stop the subscriber separately
from its governing client, it need not capture the SubscriberFunc value at all.
One downside of this approach is that a slow or deadlocked callback could block
client's service routine and thus stall all other subscriptions on that client,
However, this can already happen more broadly if a subscriber fails to service
its delivery channel in a timely manner, it just feeds back more immediately.
Updates #17487
Change-Id: I64592d786005177aa9fd445c263178ed415784d5
Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>
It is a programming error to Publish or Subscribe on a closed Client, but now
the way you discover that is by getting a panic from down in the machinery of
the bus after the client state has been cleaned up.
To provide a more helpful error, let's panic explicitly when that happens and
say what went wrong ("the client is closed"), by preventing subscriptions from
interleaving with closure of the client. With this change, either an attachment
fails outright (because the client is already closed) or completes and then
shuts down in good order in the normal course.
This does not change the semantics of the client, publishers, or subscribers,
it's just making the failure more eager so we can attach explanatory text.
Updates #15160
Change-Id: Ia492f4c1dea7535aec2cdcc2e5ea5410ed5218d2
Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>
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>
James Tucker
Will Norris
Brad Fitzpatrick
M. J. Fromberger
Claus Lensbøl
Nick Khyl
David Anderson