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>
Two changes that share the same intent of reducing per-T duplication
in code that doesn't actually depend on T:
1. Hoist the non-generic portion of newSubscriberFunc[T] into a
newSubscriberFuncCore() helper. The hoisted work is the time
timer setup, the subscriberFuncCore allocation, and the
unregister closure (which captures only the non-generic
reflect.Type and *subscribeState). The generic body now does
only the two T-bound things it has to: compute reflect.TypeFor[T]
and create the dispatch closure.
Effect on the per-shape-stencil body of newSubscriberFunc[T]:
before: 523 B per shape (in synthetic test)
after: 293 B per shape (-230 B per shape; -56% on this body)
2. Cache reflect.Type.String() once at construction (in core.typeName)
instead of recomputing it every time the dispatch closure runs.
The dispatch closure also now takes the *subscriberFuncCore directly
rather than building an intermediate dispatchFuncState struct on
every call.
Effect on the dispatch closure body (newSubscriberFunc[T].func1):
before: 581 B per shape
after: 480 B per shape (-101 B per shape; -17%)
Combined effect on tailscaled (linux/amd64):
named-symbol savings via symcost: ~7 KB
stripped binary delta: -8 KB (page-quantized)
arm64 binary delta: 0 (page-quantized)
cumulative reduction from baseline (5167ff412):
linux/amd64: -110,592 bytes (-0.391%)
linux/arm64: -131,072 bytes (-0.499%)
Throughput is also improved by the typeName cache: BenchmarkBasic
goes from 2018 ns/op to 1864 ns/op (-7.6%) because the dispatch hot
path no longer allocates a string on every event.
Updates #12614
Change-Id: Ib3a3d6796785e16506330ec034e1144580d467a3
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>
The (*SubscriberFunc[T]).dispatch method body — a ~40-line select
loop with slow-subscriber timer, snapshot handling, ctx-cancel
draining, and a CI stack-dump branch — was previously fully
duplicated by the Go compiler for every distinct GC shape of T.
None of that body actually depends on T except for the type
assertion and the user callback invocation.
This change moves the loop body into a non-generic dispatchFunc()
helper, leaving (*SubscriberFunc[T]).dispatch as a tiny wrapper
that:
- performs the vals.Peek().Event.(T) type assertion
- spawns the callback goroutine via `go runFuncCallback(s.read,
t, callDone)` — a regular generic function call, not a closure,
so that `go` binds the args to the goroutine's frame instead of
allocating a closure on the heap. This preserves the
zero-extra-allocation behavior of the original
(*SubscriberFunc[T]).runCallback method.
- resolves T's name via reflect.TypeFor[T]().String() (cached on
the stack rather than recomputed on each %T formatting)
- calls dispatchFunc with the callDone channel
The %T formatting in the original logf calls is replaced with %s
on the resolved name string, removing per-T fmt instantiations.
A new BenchmarkBasicFuncThroughput is added alongside the existing
BenchmarkBasicThroughput so per-event allocation behavior on the
SubscribeFunc dispatch path is covered by the benchmark suite.
Measured impact (util/eventbus/sizetest):
SubscriberFunc per-flow attribution:
linux/amd64: 912.5 B/flow -> 840.8 B/flow (-71.7 B/flow)
linux/arm64: 917.5 B/flow -> 849.9 B/flow (-67.6 B/flow)
The total per-flow size delta on amd64 dropped from 3,096.6 B to
3,039.2 B (-57 B/flow). The arm64 total stayed at 3,145.7 B
because the linker's page-aligned section sizing absorbed the
improvement on this binary; the symcost-attributed per-receiver
number is the real signal.
Behavior is unchanged: BenchmarkBasicThroughput stays at 0
allocs/op and BenchmarkBasicFuncThroughput holds at the same 2
allocs/op, 144 B/op as the prior eventbus implementation. All
eventbus tests pass.
Updates #12614
Change-Id: I85f933f50f58cd25bbfe5cc46bdda7aab22f0bf7
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>
Prior to this change a SubscriberFunc treated the call to the subscriber's
function as the completion of delivery. But that means when we are closing the
subscriber, that callback could continue to execute for some time after the
close returns.
For channel-based subscribers that works OK because the close takes effect
before the subscriber ever sees the event. To make the two subscriber types
symmetric, we should also wait for the callback to finish before returning.
This ensures that a Close of the client means the same thing with both kinds of
subscriber.
Updates #17638
Change-Id: I82fd31bcaa4e92fab07981ac0e57e6e3a7d9d60b
Signed-off-by: M. J. Fromberger <fromberger@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>
With a channel subscriber, the subscription processing always occurs on another
goroutine. The SubscriberFunc (prior to this commit) runs its callbacks on the
client's own goroutine. This changes the semantics, though: In addition to more
directly pushing back on the publisher, a publisher and subscriber can deadlock
in a SubscriberFunc but succeed on a Subscriber. They should behave
equivalently regardless which interface they use.
Arguably the caller should deal with this by creating its own goroutine if it
needs to. However, that loses much of the benefit of the SubscriberFunc API, as
it will need to manage the lifecycle of that goroutine. So, for practical
ergonomics, let's make the SubscriberFunc do this management on the user's
behalf. (We discussed doing this in #17432, but decided not to do it yet). We
can optimize this approach further, if we need to, without changing the API.
Updates #17487
Change-Id: I19ea9e8f246f7b406711f5a16518ef7ff21a1ac9
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>
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>
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>
This makes the helpers closer in behavior to cancelable contexts
and taskgroup.Single, and makes the worker code use a more normal
and easier to reason about context.Context for shutdown.
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
Nick Khyl
David Anderson