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sync: use atomic.Bool for Once.done #73447

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8 changes: 4 additions & 4 deletions src/sync/once.go
Original file line number Diff line number Diff line change
Expand Up @@ -25,7 +25,7 @@ type Once struct {
// The hot path is inlined at every call site.
// Placing done first allows more compact instructions on some architectures (amd64/386),
// and fewer instructions (to calculate offset) on other architectures.
done atomic.Uint32
done atomic.Bool
m Mutex
}

Expand Down Expand Up @@ -64,7 +64,7 @@ func (o *Once) Do(f func()) {
// This is why the slow path falls back to a mutex, and why
// the o.done.Store must be delayed until after f returns.

if o.done.Load() == 0 {
if !o.done.Load() {
// Outlined slow-path to allow inlining of the fast-path.
o.doSlow(f)
}
Expand All @@ -73,8 +73,8 @@ func (o *Once) Do(f func()) {
func (o *Once) doSlow(f func()) {
o.m.Lock()
defer o.m.Unlock()
if o.done.Load() == 0 {
defer o.done.Store(1)
if !o.done.Load() {
defer o.done.Store(true)
f()
}
}
2 changes: 1 addition & 1 deletion test/inline_sync.go
Original file line number Diff line number Diff line change
Expand Up @@ -37,7 +37,7 @@ var once *sync.Once

func small7() { // ERROR "can inline small7"
// the Do fast path should be inlined
once.Do(small5) // ERROR "inlining call to sync\.\(\*Once\)\.Do" "inlining call to atomic\.\(\*Uint32\)\.Load"
once.Do(small5) // ERROR "inlining call to sync\.\(\*Once\)\.Do" "inlining call to atomic\.\(\*Bool\)\.Load"
}

var rwmutex *sync.RWMutex
Expand Down