From c138d573a3568151502a39ba9257cf657dcc8a4c Mon Sep 17 00:00:00 2001
From: Jason Barron <jason@ownersroom.com>
Date: Wed, 7 Nov 2018 09:17:02 +0100
Subject: [PATCH] Fix panic due to missing mutex lock/unlock

We cannot just re-create the 'tempLabels' struct here without first
checking if the mutex is locked. The simplest solution is to have a
reset() function which resets the internal map, but preserves the
mutex state.
---
 core.go      |  2 +-
 core_test.go | 28 ++++++++++++++++++++++++++++
 label.go     |  6 ++++++
 3 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/core.go b/core.go
index 886d665..5684fe4 100644
--- a/core.go
+++ b/core.go
@@ -82,7 +82,7 @@ func (c *core) Write(ent zapcore.Entry, fields []zapcore.Field) error {
 	fields = append(fields, labelsField(c.allLabels()))
 	fields = c.withSourceLocation(ent, fields)
 
-	c.tempLabels = newLabels()
+	c.tempLabels.reset()
 
 	return c.Core.Write(ent, fields)
 }
diff --git a/core_test.go b/core_test.go
index cef1233..d640c90 100644
--- a/core_test.go
+++ b/core_test.go
@@ -2,6 +2,7 @@ package zapdriver
 
 import (
 	"runtime"
+	"sync/atomic"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -110,6 +111,33 @@ func TestWrite(t *testing.T) {
 	assert.NotNil(t, logs.All()[0].ContextMap()["labels"])
 }
 
+func TestWriteConcurrent(t *testing.T) {
+	temp := newLabels()
+	temp.store = map[string]string{"one": "1", "two": "2"}
+	goRoutines := 8
+	counter := int32(10000)
+
+	debugcore, logs := observer.New(zapcore.DebugLevel)
+	core := &core{debugcore, newLabels(), temp}
+
+	fields := []zap.Field{
+		zap.String("hello", "world"),
+		Label("one", "value"),
+		Label("two", "value"),
+	}
+
+	for i := 0; i < goRoutines; i++ {
+		go func() {
+			for atomic.AddInt32(&counter, -1) > 0 {
+				err := core.Write(zapcore.Entry{}, fields)
+				require.NoError(t, err)
+			}
+		}()
+	}
+
+	assert.NotNil(t, logs.All()[0].ContextMap()["labels"])
+}
+
 func TestWithAndWrite(t *testing.T) {
 	debugcore, logs := observer.New(zapcore.DebugLevel)
 	core := zapcore.Core(&core{debugcore, newLabels(), newLabels()})
diff --git a/label.go b/label.go
index 0a2d149..07656c9 100644
--- a/label.go
+++ b/label.go
@@ -58,6 +58,12 @@ func (l *labels) Add(key, value string) {
 	l.mutex.Unlock()
 }
 
+func (l *labels) reset() {
+	l.mutex.Lock()
+	l.store = map[string]string{}
+	l.mutex.Unlock()
+}
+
 func (l labels) MarshalLogObject(enc zapcore.ObjectEncoder) error {
 	l.mutex.RLock()
 	for k, v := range l.store {