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>
James Tucker
e7415e6393