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>
James Tucker
4eec4423b4