log: fix data race on log.Output
There was unprotected access to Logger.flag in log.Output which
could lead to data race in cases when log.SetFlags called simultaneously.
For example, "hot" switching on/off debug-mode for Logger by log.SetFlags
while application still writing logs.
Fixes #21935
Change-Id: I36be25f23cad44cde62ed1af28a30d276400e1b8
Reviewed-on: https://go-review.googlesource.com/64710
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/log/log.go b/src/log/log.go
index a6add87..2b7c57f 100644
--- a/src/log/log.go
+++ b/src/log/log.go
@@ -147,11 +147,7 @@
// provided for generality, although at the moment on all pre-defined
// paths it will be 2.
func (l *Logger) Output(calldepth int, s string) error {
- // Get time early if we need it.
- var now time.Time
- if l.flag&(Ldate|Ltime|Lmicroseconds) != 0 {
- now = time.Now()
- }
+ now := time.Now() // get this early.
var file string
var line int
l.mu.Lock()
diff --git a/src/log/log_test.go b/src/log/log_test.go
index 966fdf3..adc15e7 100644
--- a/src/log/log_test.go
+++ b/src/log/log_test.go
@@ -88,6 +88,17 @@
}
}
+func TestOutputRace(t *testing.T) {
+ var b bytes.Buffer
+ l := New(&b, "", 0)
+ for i := 0; i < 100; i++ {
+ go func() {
+ l.SetFlags(0)
+ }()
+ l.Output(0, "")
+ }
+}
+
func TestFlagAndPrefixSetting(t *testing.T) {
var b bytes.Buffer
l := New(&b, "Test:", LstdFlags)
