context: Uniformly pass cancelCtx by pointer.
cancelCtx has an embedded sync.Mutex. This change causes an extra
allocation when creating a new timerCtx via WithDeadline, but that seems
minor when compared with better locking discipline. If it turns out to
be a problem, the whole cancelCtx struct can be flattened into timerCtx.
Addresses part of golang/go#14839.
Change-Id: Ie86ed1b63592b521aefde747d5fafcd49ac18178
Reviewed-on: https://go-review.googlesource.com/20840
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/context/context.go b/context/context.go
index 77b64d0..19235cf 100644
--- a/context/context.go
+++ b/context/context.go
@@ -210,13 +210,13 @@
// call cancel as soon as the operations running in this Context complete.
func WithCancel(parent Context) (ctx Context, cancel CancelFunc) {
c := newCancelCtx(parent)
- propagateCancel(parent, &c)
- return &c, func() { c.cancel(true, Canceled) }
+ propagateCancel(parent, c)
+ return c, func() { c.cancel(true, Canceled) }
}
// newCancelCtx returns an initialized cancelCtx.
-func newCancelCtx(parent Context) cancelCtx {
- return cancelCtx{
+func newCancelCtx(parent Context) *cancelCtx {
+ return &cancelCtx{
Context: parent,
done: make(chan struct{}),
}
@@ -259,7 +259,7 @@
case *cancelCtx:
return c, true
case *timerCtx:
- return &c.cancelCtx, true
+ return c.cancelCtx, true
case *valueCtx:
parent = c.Context
default:
@@ -377,7 +377,7 @@
// 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
