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runtime: convert semaRoot.nwait to atomic type

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For #53821

Change-Id: I686fe81268f70acc6a4c3e6b1d3ed0e07bb0d61c
Reviewed-on: https://go-review.googlesource.com/c/go/+/425775
Run-TryBot: xie cui <523516579@qq.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
This commit is contained in:
cuiweixie 2022-08-26 10:27:57 +08:00 • committed by Michael Knyszek
parent 6e74c4116a
commit fa0e3bffb4
2 changed files with 8 additions and 8 deletions
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2
src/runtime/export_test.go
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@ -1164,7 +1164,7 @@ var Semrelease1 = semrelease1
func SemNwait(addr *uint32) uint32 { func SemNwait(addr *uint32) uint32 {
root := semtable.rootFor(addr) root := semtable.rootFor(addr)
return atomic.Load(&root.nwait) return root.nwait.Load()
} }
const SemTableSize = semTabSize const SemTableSize = semTabSize

14
src/runtime/sema.go
View file

@ -39,8 +39,8 @@ import (
// BenchmarkSemTable/OneAddrCollision/* for a benchmark that exercises this. // BenchmarkSemTable/OneAddrCollision/* for a benchmark that exercises this.
type semaRoot struct { type semaRoot struct {
lock mutex lock mutex
treap *sudog // root of balanced tree of unique waiters. treap *sudog // root of balanced tree of unique waiters.
nwait uint32 // Number of waiters. Read w/o the lock. nwait atomic.Uint32 // Number of waiters. Read w/o the lock.
} }
var semtable semTable var semtable semTable
@ -137,10 +137,10 @@ func semacquire1(addr *uint32, lifo bool, profile semaProfileFlags, skipframes i
for { for {
lockWithRank(&root.lock, lockRankRoot) lockWithRank(&root.lock, lockRankRoot)
// Add ourselves to nwait to disable "easy case" in semrelease. // Add ourselves to nwait to disable "easy case" in semrelease.
atomic.Xadd(&root.nwait, 1) root.nwait.Add(1)
// Check cansemacquire to avoid missed wakeup. // Check cansemacquire to avoid missed wakeup.
if cansemacquire(addr) { if cansemacquire(addr) {
atomic.Xadd(&root.nwait, -1) root.nwait.Add(-1)
unlock(&root.lock) unlock(&root.lock)
break break
} }
@ -169,13 +169,13 @@ func semrelease1(addr *uint32, handoff bool, skipframes int) {
// Easy case: no waiters? // Easy case: no waiters?
// This check must happen after the xadd, to avoid a missed wakeup // This check must happen after the xadd, to avoid a missed wakeup
// (see loop in semacquire). // (see loop in semacquire).
if atomic.Load(&root.nwait) == 0 { if root.nwait.Load() == 0 {
return return
} }
// Harder case: search for a waiter and wake it. // Harder case: search for a waiter and wake it.
lockWithRank(&root.lock, lockRankRoot) lockWithRank(&root.lock, lockRankRoot)
if atomic.Load(&root.nwait) == 0 { if root.nwait.Load() == 0 {
// The count is already consumed by another goroutine, // The count is already consumed by another goroutine,
// so no need to wake up another goroutine. // so no need to wake up another goroutine.
unlock(&root.lock) unlock(&root.lock)
@ -183,7 +183,7 @@ func semrelease1(addr *uint32, handoff bool, skipframes int) {
} }
s, t0 := root.dequeue(addr) s, t0 := root.dequeue(addr)
if s != nil { if s != nil {
atomic.Xadd(&root.nwait, -1) root.nwait.Add(-1)
} }
unlock(&root.lock) unlock(&root.lock)
if s != nil { // May be slow or even yield, so unlock first if s != nil { // May be slow or even yield, so unlock first