mirror of
https://github.com/tailscale/tailscale.git
synced 2026-05-09 15:44:33 -04:00
0def0f19bd
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>