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>
James Tucker
d72cde1a6b