context: remove one allocation in timerCtx

Embed the cancelCtx into timerCtx, instead of allocating both separately.

name                               old time/op    new time/op    delta
WithTimeout/concurrency=40-16        2.21µs ±11%    2.08µs ± 5%   -5.76%  (p=0.011 n=10+10)
WithTimeout/concurrency=4000-16      1.94µs ± 6%    1.86µs ±10%     ~     (p=0.099 n=9+10)
WithTimeout/concurrency=400000-16    1.86µs ± 7%    1.83µs ±10%     ~     (p=0.353 n=10+10)

name                               old alloc/op   new alloc/op   delta
WithTimeout/concurrency=40-16        2.56kB ± 0%    2.40kB ± 0%   -6.25%  (p=0.001 n=8+9)
WithTimeout/concurrency=4000-16      2.56kB ± 0%    2.40kB ± 0%   -6.25%  (p=0.000 n=9+10)
WithTimeout/concurrency=400000-16    2.56kB ± 0%    2.40kB ± 0%   -6.26%  (p=0.000 n=9+9)

name                               old allocs/op  new allocs/op  delta
WithTimeout/concurrency=40-16          50.0 ± 0%      40.0 ± 0%  -20.00%  (p=0.000 n=10+10)
WithTimeout/concurrency=4000-16        50.0 ± 0%      40.0 ± 0%  -20.00%  (p=0.000 n=10+10)
WithTimeout/concurrency=400000-16      50.0 ± 0%      40.0 ± 0%  -20.00%  (p=0.000 n=10+10)

Change-Id: Ia0460db3b8412fbaa6f1539fd6b4fb1b873896c4
Reviewed-on: https://go-review.googlesource.com/c/go/+/463999
Reviewed-by: Damien Neil <dneil@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>

diff --git a/src/context/context.go b/src/context/context.go
index 6bf6ec8dcc985cf8f5246d077d9d09090516e566..d6ed7443e9091552ee64d9abedf75af5d37b182d 100644 (file)
--- a/src/context/context.go
+++ b/src/context/context.go
@@ -272,7 +272,7 @@ func withCancel(parent Context) *cancelCtx {
        if parent == nil {
                panic("cannot create context from nil parent")
        }
-       c := newCancelCtx(parent)
+       c := &cancelCtx{Context: parent}
        propagateCancel(parent, c)
        return c
 }
@@ -292,11 +292,6 @@ func Cause(c Context) error {
        return nil
 }
 
-// newCancelCtx returns an initialized cancelCtx.
-func newCancelCtx(parent Context) *cancelCtx {
-       return &cancelCtx{Context: parent}
-}
-
 // goroutines counts the number of goroutines ever created; for testing.
 var goroutines atomic.Int32
 
@@ -507,7 +502,7 @@ func WithDeadlineCause(parent Context, d time.Time, cause error) (Context, Cance
                return WithCancel(parent)
        }
        c := &timerCtx{
-               cancelCtx: newCancelCtx(parent),
+               cancelCtx: cancelCtx{Context: parent},
                deadline:  d,
        }
        propagateCancel(parent, c)
@@ -530,7 +525,7 @@ func WithDeadlineCause(parent Context, d time.Time, cause error) (Context, Cance
 // implement Done and Err. It implements cancel by stopping its timer then
 // delegating to cancelCtx.cancel.
 type timerCtx struct {
-       *cancelCtx
+       cancelCtx
        timer *time.Timer // Under cancelCtx.mu.
 
        deadline time.Time
@@ -655,7 +650,7 @@ func value(c Context, key any) any {
                        c = ctx.Context
                case *timerCtx:
                        if key == &cancelCtxKey {
-                               return ctx.cancelCtx
+                               return &ctx.cancelCtx
                        }
                        c = ctx.Context
                case *emptyCtx: