runtime: fix futexsleep test on freebsd/386

Fixes #7194.

LGTM=bradfitz
R=golang-codereviews, bradfitz
CC=golang-codereviews
https://golang.org/cl/72310043

src/pkg/runtime/futex_test.go

@@ -2,33 +2,70 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Futex is only available on Dragonfly, FreeBSD and Linux.
-// The race detector emits calls to split stack functions so it breaks the test.
+// Futex is only available on DragonFly BSD, FreeBSD and Linux.
+// The race detector emits calls to split stack functions so it breaks
+// the test.
+
 // +build dragonfly freebsd linux
 // +build !race
 
 package runtime_test
 
 import (
-	. "runtime"
+	"runtime"
 	"testing"
 	"time"
 )
 
+type futexsleepTest struct {
+	mtx uint32
+	ns  int64
+	msg string
+	ch  chan futexsleepTest
+}
+
+var futexsleepTests = []futexsleepTest{
+	beforeY2038: {mtx: 0, ns: 86400 * 1e9, msg: "before the year 2038", ch: make(chan futexsleepTest, 1)},
+	afterY2038:  {mtx: 0, ns: (1<<31 + 100) * 1e9, msg: "after the year 2038", ch: make(chan futexsleepTest, 1)},
+}
+
+const (
+	beforeY2038 = iota
+	afterY2038
+)
+
 func TestFutexsleep(t *testing.T) {
-	ch := make(chan bool, 1)
-	var dummy uint32
 	start := time.Now()
-	go func() {
-		Entersyscall()
-		Futexsleep(&dummy, 0, (1<<31+100)*1e9)
-		Exitsyscall()
-		ch <- true
-	}()
+	for _, tt := range futexsleepTests {
+		go func(tt futexsleepTest) {
+			runtime.Entersyscall()
+			runtime.Futexsleep(&tt.mtx, tt.mtx, tt.ns)
+			runtime.Exitsyscall()
+			tt.ch <- tt
+		}(tt)
+	}
+loop:
+	for {
 		select {
-	case <-ch:
-		t.Errorf("futexsleep finished early after %s!", time.Since(start))
+		case tt := <-futexsleepTests[beforeY2038].ch:
+			t.Errorf("futexsleep test %q finished early after %s", tt.msg, time.Since(start))
+			break loop
+		case tt := <-futexsleepTests[afterY2038].ch:
+			// Looks like FreeBSD 10 kernel has changed
+			// the semantics of timedwait on userspace
+			// mutex to make broken stuff look broken.
+			switch {
+			case runtime.GOOS == "freebsd" && runtime.GOARCH == "386":
+				t.Log("freebsd/386 may not work correctly after the year 2038, see golang.org/issue/7194")
+			default:
+				t.Errorf("futexsleep test %q finished early after %s", tt.msg, time.Since(start))
+				break loop
+			}
 		case <-time.After(time.Second):
-		Futexwakeup(&dummy, 1)
+			break loop
+		}
+	}
+	for _, tt := range futexsleepTests {
+		runtime.Futexwakeup(&tt.mtx, 1)
 	}
 }