runtime: convert timer.status to atomic type

For #53821

Change-Id: I7cb6a16626964d5023b96609d9921bfe4a679d8f
GitHub-Last-Rev: ddfce125be4aa565aa4d2081841c649bf2f71459
GitHub-Pull-Request: golang/go#54865
Reviewed-on: https://go-review.googlesource.com/c/go/+/428196
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Jenny Rakoczy <jenny@golang.org>
Auto-Submit: Jenny Rakoczy <jenny@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 44 insertions, 43 deletions

diff --git a/src/runtime/time.go b/src/runtime/time.go
index 945756109a..6cd70b7aed 100644
--- a/src/runtime/time.go
+++ b/src/runtime/time.go
@@ -36,7 +36,7 @@ type timer struct {
 	nextwhen int64
 
 	// The status field holds one of the values below.
-	status uint32
+	status atomic.Uint32
 }
 
 // Code outside this file has to be careful in using a timer value.
@@ -249,6 +249,7 @@ func goroutineReady(arg any, seq uintptr) {
 	goready(arg.(*g), 0)
 }
 
+// Note: this changes some unsynchronized operations to synchronized operations
 // addtimer adds a timer to the current P.
 // This should only be called with a newly created timer.
 // That avoids the risk of changing the when field of a timer in some P's heap,
@@ -263,10 +264,10 @@ func addtimer(t *timer) {
 	if t.period < 0 {
 		throw("timer period must be non-negative")
 	}
-	if t.status != timerNoStatus {
+	if t.status.Load() != timerNoStatus {
 		throw("addtimer called with initialized timer")
 	}
-	t.status = timerWaiting
+	t.status.Store(timerWaiting)
 
 	when := t.when
 
@@ -312,17 +313,17 @@ func doaddtimer(pp *p, t *timer) {
 // Reports whether the timer was removed before it was run.
 func deltimer(t *timer) bool {
 	for {
-		switch s := atomic.Load(&t.status); s {
+		switch s := t.status.Load(); s {
 		case timerWaiting, timerModifiedLater:
 			// Prevent preemption while the timer is in timerModifying.
 			// This could lead to a self-deadlock. See #38070.
 			mp := acquirem()
-			if atomic.Cas(&t.status, s, timerModifying) {
+			if t.status.CompareAndSwap(s, timerModifying) {
 				// Must fetch t.pp before changing status,
 				// as cleantimers in another goroutine
 				// can clear t.pp of a timerDeleted timer.
 				tpp := t.pp.ptr()
-				if !atomic.Cas(&t.status, timerModifying, timerDeleted) {
+				if !t.status.CompareAndSwap(timerModifying, timerDeleted) {
 					badTimer()
 				}
 				releasem(mp)
@@ -336,11 +337,11 @@ func deltimer(t *timer) bool {
 			// Prevent preemption while the timer is in timerModifying.
 			// This could lead to a self-deadlock. See #38070.
 			mp := acquirem()
-			if atomic.Cas(&t.status, s, timerModifying) {
+			if t.status.CompareAndSwap(s, timerModifying) {
 				// Must fetch t.pp before setting status
 				// to timerDeleted.
 				tpp := t.pp.ptr()
-				if !atomic.Cas(&t.status, timerModifying, timerDeleted) {
+				if !t.status.CompareAndSwap(timerModifying, timerDeleted) {
 					badTimer()
 				}
 				releasem(mp)
@@ -449,12 +450,12 @@ func modtimer(t *timer, when, period int64, f func(any, uintptr), arg any, seq u
 	var mp *m
 loop:
 	for {
-		switch status = atomic.Load(&t.status); status {
+		switch status = t.status.Load(); status {
 		case timerWaiting, timerModifiedEarlier, timerModifiedLater:
 			// Prevent preemption while the timer is in timerModifying.
 			// This could lead to a self-deadlock. See #38070.
 			mp = acquirem()
-			if atomic.Cas(&t.status, status, timerModifying) {
+			if t.status.CompareAndSwap(status, timerModifying) {
 				pending = true // timer not yet run
 				break loop
 			}
@@ -466,7 +467,7 @@ loop:
 
 			// Timer was already run and t is no longer in a heap.
 			// Act like addtimer.
-			if atomic.Cas(&t.status, status, timerModifying) {
+			if t.status.CompareAndSwap(status, timerModifying) {
 				wasRemoved = true
 				pending = false // timer already run or stopped
 				break loop
@@ -476,7 +477,7 @@ loop:
 			// Prevent preemption while the timer is in timerModifying.
 			// This could lead to a self-deadlock. See #38070.
 			mp = acquirem()
-			if atomic.Cas(&t.status, status, timerModifying) {
+			if t.status.CompareAndSwap(status, timerModifying) {
 				t.pp.ptr().deletedTimers.Add(-1)
 				pending = false // timer already stopped
 				break loop
@@ -506,7 +507,7 @@ loop:
 		lock(&pp.timersLock)
 		doaddtimer(pp, t)
 		unlock(&pp.timersLock)
-		if !atomic.Cas(&t.status, timerModifying, timerWaiting) {
+		if !t.status.CompareAndSwap(timerModifying, timerWaiting) {
 			badTimer()
 		}
 		releasem(mp)
@@ -531,7 +532,7 @@ loop:
 		}
 
 		// Set the new status of the timer.
-		if !atomic.Cas(&t.status, timerModifying, newStatus) {
+		if !t.status.CompareAndSwap(timerModifying, newStatus) {
 			badTimer()
 		}
 		releasem(mp)
@@ -577,18 +578,18 @@ func cleantimers(pp *p) {
 		if t.pp.ptr() != pp {
 			throw("cleantimers: bad p")
 		}
-		switch s := atomic.Load(&t.status); s {
+		switch s := t.status.Load(); s {
 		case timerDeleted:
-			if !atomic.Cas(&t.status, s, timerRemoving) {
+			if !t.status.CompareAndSwap(s, timerRemoving) {
 				continue
 			}
 			dodeltimer0(pp)
-			if !atomic.Cas(&t.status, timerRemoving, timerRemoved) {
+			if !t.status.CompareAndSwap(timerRemoving, timerRemoved) {
 				badTimer()
 			}
 			pp.deletedTimers.Add(-1)
 		case timerModifiedEarlier, timerModifiedLater:
-			if !atomic.Cas(&t.status, s, timerMoving) {
+			if !t.status.CompareAndSwap(s, timerMoving) {
 				continue
 			}
 			// Now we can change the when field.
@@ -596,7 +597,7 @@ func cleantimers(pp *p) {
 			// Move t to the right position.
 			dodeltimer0(pp)
 			doaddtimer(pp, t)
-			if !atomic.Cas(&t.status, timerMoving, timerWaiting) {
+			if !t.status.CompareAndSwap(timerMoving, timerWaiting) {
 				badTimer()
 			}
 		default:
@@ -614,30 +615,30 @@ func moveTimers(pp *p, timers []*timer) {
 	for _, t := range timers {
 	loop:
 		for {
-			switch s := atomic.Load(&t.status); s {
+			switch s := t.status.Load(); s {
 			case timerWaiting:
-				if !atomic.Cas(&t.status, s, timerMoving) {
+				if !t.status.CompareAndSwap(s, timerMoving) {
 					continue
 				}
 				t.pp = 0
 				doaddtimer(pp, t)
-				if !atomic.Cas(&t.status, timerMoving, timerWaiting) {
+				if !t.status.CompareAndSwap(timerMoving, timerWaiting) {
 					badTimer()
 				}
 				break loop
 			case timerModifiedEarlier, timerModifiedLater:
-				if !atomic.Cas(&t.status, s, timerMoving) {
+				if !t.status.CompareAndSwap(s, timerMoving) {
 					continue
 				}
 				t.when = t.nextwhen
 				t.pp = 0
 				doaddtimer(pp, t)
-				if !atomic.Cas(&t.status, timerMoving, timerWaiting) {
+				if !t.status.CompareAndSwap(timerMoving, timerWaiting) {
 					badTimer()
 				}
 				break loop
 			case timerDeleted:
-				if !atomic.Cas(&t.status, s, timerRemoved) {
+				if !t.status.CompareAndSwap(s, timerRemoved) {
 					continue
 				}
 				t.pp = 0
@@ -688,11 +689,11 @@ func adjusttimers(pp *p, now int64) {
 		if t.pp.ptr() != pp {
 			throw("adjusttimers: bad p")
 		}
-		switch s := atomic.Load(&t.status); s {
+		switch s := t.status.Load(); s {
 		case timerDeleted:
-			if atomic.Cas(&t.status, s, timerRemoving) {
+			if t.status.CompareAndSwap(s, timerRemoving) {
 				changed := dodeltimer(pp, i)
-				if !atomic.Cas(&t.status, timerRemoving, timerRemoved) {
+				if !t.status.CompareAndSwap(timerRemoving, timerRemoved) {
 					badTimer()
 				}
 				pp.deletedTimers.Add(-1)
@@ -701,7 +702,7 @@ func adjusttimers(pp *p, now int64) {
 				i = changed - 1
 			}
 		case timerModifiedEarlier, timerModifiedLater:
-			if atomic.Cas(&t.status, s, timerMoving) {
+			if t.status.CompareAndSwap(s, timerMoving) {
 				// Now we can change the when field.
 				t.when = t.nextwhen
 				// Take t off the heap, and hold onto it.
@@ -741,7 +742,7 @@ func adjusttimers(pp *p, now int64) {
 func addAdjustedTimers(pp *p, moved []*timer) {
 	for _, t := range moved {
 		doaddtimer(pp, t)
-		if !atomic.Cas(&t.status, timerMoving, timerWaiting) {
+		if !t.status.CompareAndSwap(timerMoving, timerWaiting) {
 			badTimer()
 		}
 	}
@@ -776,14 +777,14 @@ func runtimer(pp *p, now int64) int64 {
 		if t.pp.ptr() != pp {
 			throw("runtimer: bad p")
 		}
-		switch s := atomic.Load(&t.status); s {
+		switch s := t.status.Load(); s {
 		case timerWaiting:
 			if t.when > now {
 				// Not ready to run.
 				return t.when
 			}
 
-			if !atomic.Cas(&t.status, s, timerRunning) {
+			if !t.status.CompareAndSwap(s, timerRunning) {
 				continue
 			}
 			// Note that runOneTimer may temporarily unlock
@@ -792,11 +793,11 @@ func runtimer(pp *p, now int64) int64 {
 			return 0
 
 		case timerDeleted:
-			if !atomic.Cas(&t.status, s, timerRemoving) {
+			if !t.status.CompareAndSwap(s, timerRemoving) {
 				continue
 			}
 			dodeltimer0(pp)
-			if !atomic.Cas(&t.status, timerRemoving, timerRemoved) {
+			if !t.status.CompareAndSwap(timerRemoving, timerRemoved) {
 				badTimer()
 			}
 			pp.deletedTimers.Add(-1)
@@ -805,13 +806,13 @@ func runtimer(pp *p, now int64) int64 {
 			}
 
 		case timerModifiedEarlier, timerModifiedLater:
-			if !atomic.Cas(&t.status, s, timerMoving) {
+			if !t.status.CompareAndSwap(s, timerMoving) {
 				continue
 			}
 			t.when = t.nextwhen
 			dodeltimer0(pp)
 			doaddtimer(pp, t)
-			if !atomic.Cas(&t.status, timerMoving, timerWaiting) {
+			if !t.status.CompareAndSwap(timerMoving, timerWaiting) {
 				badTimer()
 			}
 
@@ -858,14 +859,14 @@ func runOneTimer(pp *p, t *timer, now int64) {
 			t.when = maxWhen
 		}
 		siftdownTimer(pp.timers, 0)
-		if !atomic.Cas(&t.status, timerRunning, timerWaiting) {
+		if !t.status.CompareAndSwap(timerRunning, timerWaiting) {
 			badTimer()
 		}
 		updateTimer0When(pp)
 	} else {
 		// Remove from heap.
 		dodeltimer0(pp)
-		if !atomic.Cas(&t.status, timerRunning, timerNoStatus) {
+		if !t.status.CompareAndSwap(timerRunning, timerNoStatus) {
 			badTimer()
 		}
 	}
@@ -912,7 +913,7 @@ func clearDeletedTimers(pp *p) {
 nextTimer:
 	for _, t := range timers {
 		for {
-			switch s := atomic.Load(&t.status); s {
+			switch s := t.status.Load(); s {
 			case timerWaiting:
 				if changedHeap {
 					timers[to] = t
@@ -921,22 +922,22 @@ nextTimer:
 				to++
 				continue nextTimer
 			case timerModifiedEarlier, timerModifiedLater:
-				if atomic.Cas(&t.status, s, timerMoving) {
+				if t.status.CompareAndSwap(s, timerMoving) {
 					t.when = t.nextwhen
 					timers[to] = t
 					siftupTimer(timers, to)
 					to++
 					changedHeap = true
-					if !atomic.Cas(&t.status, timerMoving, timerWaiting) {
+					if !t.status.CompareAndSwap(timerMoving, timerWaiting) {
 						badTimer()
 					}
 					continue nextTimer
 				}
 			case timerDeleted:
-				if atomic.Cas(&t.status, s, timerRemoving) {
+				if t.status.CompareAndSwap(s, timerRemoving) {
 					t.pp = 0
 					cdel++
-					if !atomic.Cas(&t.status, timerRemoving, timerRemoved) {
+					if !t.status.CompareAndSwap(timerRemoving, timerRemoved) {
 						badTimer()
 					}
 					changedHeap = true