Race in setting Config.Level (#71)

* Race in setting Config.Level: Add failing test

* Fix race

* test shouldn't check for timing

http_logging_test.go

@@ -116,7 +116,7 @@ func TestLogAndCall(t *testing.T) {
 	w.Flush()
 	actual = b.String()
 	//nolint: lll
-	expectedPrefix = `{"level":"info","msg":"test-log-and-call2","method":"","url":"/tea","host":"","proto":"","remote_addr":"","header.x-forwarded-host":"foo2.fortio.org","status":418,"size":5,"microsec":10`
+	expectedPrefix = `{"level":"info","msg":"test-log-and-call2","method":"","url":"/tea","host":"","proto":"","remote_addr":"","header.x-forwarded-host":"foo2.fortio.org","status":418,"size":5,`
 	if !strings.HasPrefix(actual, expectedPrefix) {
 		t.Errorf("unexpected:\n%s\nvs should start with:\n%s\n", actual, expectedPrefix)
 	}

logger.go

@@ -327,7 +327,9 @@ func setLogLevel(lvl Level, logChange bool) Level {
 			logUnconditionalf(Config.LogFileAndLine, Info, "Log level is now %d %s (was %d %s)", lvl, lvl.String(), prev, prev.String())
 		}
 		setLevel(lvl)
+		jWriter.mutex.Lock()
 		Config.Level = lvl.String()
+		jWriter.mutex.Unlock()
 	}
 	return prev
 }
@@ -368,6 +370,7 @@ func Logf(lvl Level, format string, rest ...interface{}) {
 }
 
 // Used when doing our own logging writing, in JSON/structured mode (and some color variants as well, misnomer).
+// Also reusing that lock to update global Config.Level.
 var (
 	jWriter = jsonWriter{w: os.Stderr, tsBuf: make([]byte, 0, 32)}
 )

logger_test.go

@@ -957,6 +957,22 @@ func TestInvalidFile(t *testing.T) {
 	}
 }
 
+func TestConcurrentLevelSet(t *testing.T) {
+	// This test is to make sure that setting the log level concurrently
+	// doesn't cause a -race failure. Shows up in dflag/ for instance with configmap changes.
+	var wg sync.WaitGroup
+	wg.Add(int(Fatal - Verbose))
+	for i := Verbose; i < Fatal; i++ {
+		go func(lvl Level) {
+			SetLogLevel(lvl)
+			wg.Done()
+		}(i)
+	}
+	wg.Wait()
+	SetLogLevel(Info)
+	t.Logf("log level is now %s", GetLogLevel().String())
+}
+
 // --- Benchmarks
 
 // This `discard` is like io.Discard, except that io.Discard is checked explicitly