fix: deep copy the fields to avoid data race (#128)

* fix(test): use sublogger generated from With() in race detection

The new sublogger generated from With() are never used, which may cause
optimization of the sublogger, and no race condition is detected.

Use a for loop to spawn a lots of goroutines to ensure the race
condition would happen in CI.

We also need to replace the bytes.Buffer to io.Discard, since the
bytes.Buffer is also not thread-safe.

Signed-off-by: yuguorui <[email protected]>

* fix: deep copy the fields to avoid data race

sl.fields and l.fields reference the the same object, when we create
multiple goroutines and bump loggers with the With() method, the golang
race detector will complain about this.

Signed-off-by: yuguorui <[email protected]>

---------

Signed-off-by: yuguorui <[email protected]>

logger.go

@@ -334,7 +334,8 @@ func (l *Logger) With(keyvals ...interface{}) *Logger {
 	sl.b = bytes.Buffer{}
 	sl.mu = &sync.RWMutex{}
 	sl.helpers = &sync.Map{}
-	sl.fields = append(l.fields, keyvals...)
+	sl.fields = append(make([]interface{}, 0, len(l.fields)+len(keyvals)), l.fields...)
+	sl.fields = append(sl.fields, keyvals...)
 	sl.styles = &st
 	return &sl
 }

logger_test.go

@@ -2,6 +2,7 @@ package log
 
 import (
 	"bytes"
+	"fmt"
 	"io"
 	"sync"
 	"testing"
@@ -204,7 +205,7 @@ func TestLogWithPrefix(t *testing.T) {
 }
 
 func TestLogWithRaceCondition(t *testing.T) {
-	var buf bytes.Buffer
+	w := io.Discard
 	cases := []struct {
 		name string
 	}{
@@ -214,21 +215,30 @@ func TestLogWithRaceCondition(t *testing.T) {
 	}
 	for _, c := range cases {
 		t.Run(c.name, func(t *testing.T) {
-			buf.Reset()
-			l := New(&buf)
+			l := New(w)
 
 			var done sync.WaitGroup
-			done.Add(2)
 
-			go func() {
-				l.With("arg1", "val1", "arg2", "val2")
-				done.Done()
-			}()
+			longArgs := make([]interface{}, 0, 1000)
+			for i := 0; i < 1000; i++ {
+				longArgs = append(longArgs, fmt.Sprintf("arg%d", i), fmt.Sprintf("val%d", i))
+			}
+			l = l.With(longArgs...)
+
+			for i := 0; i < 100; i++ {
+				done.Add(1)
+				go func() {
+					ll := l.With("arg1", "val1", "arg2", "val2")
+					ll.Info("kinda long long log message")
+					done.Done()
+				}()
 
-			go func() {
-				l.Info("kinda long log message")
-				done.Done()
-			}()
+				done.Add(1)
+				go func() {
+					l.Info("kinda long log message")
+					done.Done()
+				}()
+			}
 			done.Wait()
 		})
 	}