fix for entry data field race condition

entry.go

@@ -78,8 +78,20 @@ func NewEntry(logger *Logger) *Entry {
 	}
 }
 
+func (entry *Entry) Dup() *Entry {
+	data := make(Fields, len(entry.Data))
+	for k, v := range entry.Data {
+		data[k] = v
+	}
+	return &Entry{Logger: entry.Logger, Data: data, Time: entry.Time, Context: entry.Context, err: entry.err}
+}
+
 // Returns the bytes representation of this entry from the formatter.
 func (entry *Entry) Bytes() ([]byte, error) {
+	return entry.bytes_nolock()
+}
+
+func (entry *Entry) bytes_nolock() ([]byte, error) {
 	return entry.Logger.Formatter.Format(entry)
 }
 
@@ -212,51 +224,49 @@ func (entry Entry) HasCaller() (has bool) {
 
 // This function is not declared with a pointer value because otherwise
 // race conditions will occur when using multiple goroutines
-func (entry Entry) log(level Level, msg string) {
+func (entry *Entry) log(level Level, msg string) {
 	var buffer *bytes.Buffer
 
-	// Default to now, but allow users to override if they want.
-	//
-	// We don't have to worry about polluting future calls to Entry#log()
-	// with this assignment because this function is declared with a
-	// non-pointer receiver.
-	if entry.Time.IsZero() {
-		entry.Time = time.Now()
+	newEntry := entry.Dup()
+
+	if newEntry.Time.IsZero() {
+		newEntry.Time = time.Now()
 	}
 
-	entry.Level = level
-	entry.Message = msg
-	entry.Logger.mu.Lock()
-	if entry.Logger.ReportCaller {
-		entry.Caller = getCaller()
-	}
-	entry.Logger.mu.Unlock()
+	newEntry.Level = level
+	newEntry.Message = msg
 
-	entry.fireHooks()
+	newEntry.Logger.mu.Lock()
+	reportCaller := newEntry.Logger.ReportCaller
+	newEntry.Logger.mu.Unlock()
+
+	if reportCaller {
+		newEntry.Caller = getCaller()
+	}
+
+	newEntry.fireHooks()
 
 	buffer = getBuffer()
 	defer func() {
-		entry.Buffer = nil
+		newEntry.Buffer = nil
 		putBuffer(buffer)
 	}()
 	buffer.Reset()
-	entry.Buffer = buffer
+	newEntry.Buffer = buffer
 
-	entry.write()
+	newEntry.write()
 
-	entry.Buffer = nil
+	newEntry.Buffer = nil
 
 	// To avoid Entry#log() returning a value that only would make sense for
 	// panic() to use in Entry#Panic(), we avoid the allocation by checking
 	// directly here.
 	if level <= PanicLevel {
-		panic(&entry)
+		panic(newEntry)
 	}
 }
 
 func (entry *Entry) fireHooks() {
-	entry.Logger.mu.Lock()
-	defer entry.Logger.mu.Unlock()
 	err := entry.Logger.Hooks.Fire(entry.Level, entry)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "Failed to fire hook: %v\n", err)
@@ -264,16 +274,18 @@ func (entry *Entry) fireHooks() {
 }
 
 func (entry *Entry) write() {
-	entry.Logger.mu.Lock()
-	defer entry.Logger.mu.Unlock()
 	serialized, err := entry.Logger.Formatter.Format(entry)
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "Failed to obtain reader, %v\n", err)
 		return
 	}
-	if _, err = entry.Logger.Out.Write(serialized); err != nil {
-		fmt.Fprintf(os.Stderr, "Failed to write to log, %v\n", err)
-	}
+	func() {
+		entry.Logger.mu.Lock()
+		defer entry.Logger.mu.Unlock()
+		if _, err := entry.Logger.Out.Write(serialized); err != nil {
+			fmt.Fprintf(os.Stderr, "Failed to write to log, %v\n", err)
+		}
+	}()
 }
 
 func (entry *Entry) Log(level Level, args ...interface{}) {