runtime: improve synchronization in TestFinalizerRegisterABI

Replace busy-wait with a channel.

Change-Id: I51ddfd5dbde15fff56c62c618570e66930902cbb
Reviewed-on: https://go-review.googlesource.com/c/go/+/310630
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

src/runtime/abi_test.go

@@ -17,36 +17,21 @@ import (
 	"os/exec"
 	"runtime"
 	"strings"
-	"sync"
 	"testing"
 	"time"
 )
 
-var regConfirmRunIface int
+var regConfirmRun chan 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) {
-	guardedWrite(&regConfirmRunPtr, *(*int)(v))
+	regConfirmRun <- *(*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) {
-	guardedWrite(&regConfirmRunIface, *(*int)(v.(*Tint)))
+	regConfirmRun <- *(*int)(v.(*Tint))
 	return 5151, 4.0, [10]byte{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
 }
 
@@ -96,15 +81,14 @@ func TestFinalizerRegisterABI(t *testing.T) {
 		name         string
 		fin          interface{}
 		confirmValue int
-		confirmRun   *int
 	}{
-		{"Pointer", regFinalizerPointer, -1, &regConfirmRunPtr},
+		{"Pointer", regFinalizerPointer, -1},
-		{"Interface", regFinalizerIface, -2, &regConfirmRunIface},
+		{"Interface", regFinalizerIface, -2},
 	}
 	for i := range tests {
 		test := &tests[i]
 		t.Run(test.name, func(t *testing.T) {
-			guardedWrite(test.confirmRun, 0)
+			regConfirmRun = make(chan int)
 
 			x := new(Tint)
 			*x = (Tint)(test.confirmValue)
@@ -116,17 +100,13 @@ func TestFinalizerRegisterABI(t *testing.T) {
 			runtime.GC()
 			runtime.GC()
 
-			for i := 0; i < 100; i++ {
+			select {
-				time.Sleep(10 * time.Millisecond)
+			case <-time.After(time.Second):
-				if guardedRead(test.confirmRun) != 0 {
-					break
-				}
-			}
-			v := guardedRead(test.confirmRun)
-			if v == 0 {
 				t.Fatal("finalizer failed to execute")
-			} else if v != test.confirmValue {
+			case gotVal := <-regConfirmRun:
-				t.Fatalf("wrong finalizer executed? regConfirmRun = %d", v)
+				if gotVal != test.confirmValue {
+					t.Fatalf("wrong finalizer executed? got %d, want %d", gotVal, test.confirmValue)
+				}
 			}
 		})
 	}