fix(logger): Make MockLogger threadsafe

internals/logger/logger.go

@@ -73,10 +73,27 @@ func Debugf(format string, v ...interface{}) {
  logger.Debug(msg)
 }
 
+type lockedBytesBuffer struct {
+ buffer bytes.Buffer
+ mutex sync.Mutex
+}
+
+func (b *lockedBytesBuffer) Write(p []byte) (int, error) {
+ b.mutex.Lock()
+ defer b.mutex.Unlock()
+ return b.buffer.Write(p)
+}
+
+func (b *lockedBytesBuffer) String() string {
+ b.mutex.Lock()
+ defer b.mutex.Unlock()
+ return b.buffer.String()
+}
+
 // MockLogger replaces the existing logger with a buffer and returns
-// the log buffer and a restore function.
-func MockLogger(prefix string) (buf *bytes.Buffer, restore func()) {
- buf = &bytes.Buffer{}
+// a Stringer returning the log buffer content and a restore function.
+func MockLogger(prefix string) (fmt.Stringer, func()) {
+ buf := &lockedBytesBuffer{}
  oldLogger := SetLogger(New(buf, prefix))
  return buf, func() {
  SetLogger(oldLogger)

internals/logger/logger_test.go

@@ -16,10 +16,12 @@ package logger_test
 
 import (
  "bytes"
+ "fmt"
  "os"
  "testing"
 
  . "gopkg.in/check.v1"
+ "gopkg.in/tomb.v2"
 
  "github.com/canonical/pebble/internals/logger"
 )
@@ -30,7 +32,7 @@ func Test(t *testing.T) { TestingT(t) }
 var _ = Suite(&LogSuite{})
 
 type LogSuite struct {
- logbuf *bytes.Buffer
+ logbuf fmt.Stringer
  restoreLogger func()
 }
 
@@ -75,3 +77,19 @@ func (s *LogSuite) TestPanicf(c *C) {
  c.Check(func() { logger.Panicf("xyzzy") }, Panics, "xyzzy")
  c.Check(s.logbuf.String(), Matches, `20\d\d-\d\d-\d\dT\d\d:\d\d:\d\d.\d\d\dZ PREFIX: PANIC xyzzy\n`)
 }
+
+func (s *LogSuite) TestMockLoggerReadWriteThreadsafe(c *C) {
+ var t tomb.Tomb
+ t.Go(func() error {
+ for i := 0; i < 100; i++ {
+ logger.Noticef("foo")
+ logger.Noticef("bar")
+ }
+ return nil
+ })
+ for i := 0; i < 10; i++ {
+ logger.Noticef(s.logbuf.String())
+ }
+ err := t.Wait()
+ c.Check(err, IsNil)
+}