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sync: use atomic.Uint32 in Once

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Change-Id: If9089f8afd78de3e62cd575f642ff96ab69e2099
GitHub-Last-Rev: 14165018d6
GitHub-Pull-Request: golang/go#63386
Reviewed-on: https://go-review.googlesource.com/c/go/+/532895
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Jorropo <jorropo.pgm@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
This commit is contained in:
mstmdev 2023-10-06 19:00:52 +00:00 committed by Gopher Robot
parent b72bbaebf9
commit be3d5fb6e6
2 changed files with 7 additions and 7 deletions
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12
src/sync/once.go
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@ -21,7 +21,7 @@ type Once struct {
// The hot path is inlined at every call site. // The hot path is inlined at every call site.
// Placing done first allows more compact instructions on some architectures (amd64/386), // Placing done first allows more compact instructions on some architectures (amd64/386),
// and fewer instructions (to calculate offset) on other architectures. // and fewer instructions (to calculate offset) on other architectures.
done uint32 done atomic.Uint32
m Mutex m Mutex
} }
@ -48,7 +48,7 @@ type Once struct {
func (o *Once) Do(f func()) { func (o *Once) Do(f func()) {
// Note: Here is an incorrect implementation of Do: // Note: Here is an incorrect implementation of Do:
// //
// if atomic.CompareAndSwapUint32(&o.done, 0, 1) { // if o.done.CompareAndSwap(0, 1) {
// f() // f()
// } // }
// //
@ -58,9 +58,9 @@ func (o *Once) Do(f func()) {
// call f, and the second would return immediately, without // call f, and the second would return immediately, without
// waiting for the first's call to f to complete. // waiting for the first's call to f to complete.
// This is why the slow path falls back to a mutex, and why // This is why the slow path falls back to a mutex, and why
// the atomic.StoreUint32 must be delayed until after f returns. // the o.done.Store must be delayed until after f returns.
if atomic.LoadUint32(&o.done) == 0 { if o.done.Load() == 0 {
// Outlined slow-path to allow inlining of the fast-path. // Outlined slow-path to allow inlining of the fast-path.
o.doSlow(f) o.doSlow(f)
} }
@ -69,8 +69,8 @@ func (o *Once) Do(f func()) {
func (o *Once) doSlow(f func()) { func (o *Once) doSlow(f func()) {
o.m.Lock() o.m.Lock()
defer o.m.Unlock() defer o.m.Unlock()
if o.done == 0 { if o.done.Load() == 0 {
defer atomic.StoreUint32(&o.done, 1) defer o.done.Store(1)
f() f()
} }
} }

2
test/inline_sync.go
View file

@ -37,7 +37,7 @@ var once *sync.Once
func small7() { // ERROR "can inline small7" func small7() { // ERROR "can inline small7"
// the Do fast path should be inlined // the Do fast path should be inlined
once.Do(small5) // ERROR "inlining call to sync\.\(\*Once\)\.Do" once.Do(small5) // ERROR "inlining call to sync\.\(\*Once\)\.Do" "inlining call to atomic\.\(\*Uint32\)\.Load"
} }
var rwmutex *sync.RWMutex var rwmutex *sync.RWMutex