runtime: fix data race in abi finalizer test

Fix a buglet in TestFinalizerRegisterABI that was causing problems
when run with GOEXPERIMENT=regabi.

Updates #40724.

Change-Id: I950c4aa3df69eada23e600f01e6804eb136ce806
Reviewed-on: https://go-review.googlesource.com/c/go/+/310077
Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

src/runtime/abi_test.go

@@ -17,21 +17,36 @@ import (
 	"os/exec"
 	"runtime"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 )
 
-var regConfirmRun int
+var regConfirmRunIface int
+var regConfirmRunPtr int
+var regConfirmMU sync.Mutex
+
+func guardedRead(p *int) int {
+	regConfirmMU.Lock()
+	defer regConfirmMU.Unlock()
+	return *p
+}
+
+func guardedWrite(p *int, v int) {
+	regConfirmMU.Lock()
+	defer regConfirmMU.Unlock()
+	*p = v
+}
 
 //go:registerparams
 func regFinalizerPointer(v *Tint) (int, float32, [10]byte) {
-	regConfirmRun = *(*int)(v)
+	guardedWrite(&regConfirmRunPtr, *(*int)(v))
 	return 5151, 4.0, [10]byte{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
 }
 
 //go:registerparams
 func regFinalizerIface(v Tinter) (int, float32, [10]byte) {
-	regConfirmRun = *(*int)(v.(*Tint))
+	guardedWrite(&regConfirmRunIface, *(*int)(v.(*Tint)))
 	return 5151, 4.0, [10]byte{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
 }
 
@@ -81,14 +96,15 @@ func TestFinalizerRegisterABI(t *testing.T) {
 		name         string
 		fin          interface{}
 		confirmValue int
+		confirmRun   *int
 	}{
-		{"Pointer", regFinalizerPointer, -1},
-		{"Interface", regFinalizerIface, -2},
+		{"Pointer", regFinalizerPointer, -1, &regConfirmRunPtr},
+		{"Interface", regFinalizerIface, -2, &regConfirmRunIface},
 	}
 	for i := range tests {
 		test := &tests[i]
 		t.Run(test.name, func(t *testing.T) {
-			regConfirmRun = 0
+			guardedWrite(test.confirmRun, 0)
 
 			x := new(Tint)
 			*x = (Tint)(test.confirmValue)
@@ -102,14 +118,15 @@ func TestFinalizerRegisterABI(t *testing.T) {
 
 			for i := 0; i < 100; i++ {
 				time.Sleep(10 * time.Millisecond)
-				if regConfirmRun != 0 {
+				if guardedRead(test.confirmRun) != 0 {
 					break
 				}
 			}
-			if regConfirmRun == 0 {
+			v := guardedRead(test.confirmRun)
+			if v == 0 {
 				t.Fatal("finalizer failed to execute")
-			} else if regConfirmRun != test.confirmValue {
-				t.Fatalf("wrong finalizer executed? regConfirmRun = %d", regConfirmRun)
+			} else if v != test.confirmValue {
+				t.Fatalf("wrong finalizer executed? regConfirmRun = %d", v)
 			}
 		})
 	}