From b042c5e48dcf4b2c19b6feea14e7f4b5eaca7ddf Mon Sep 17 00:00:00 2001
From: YACOVM <YACOVM@il.ibm.com>
Date: Fri, 30 Sep 2016 21:15:01 +0300
Subject: [PATCH] Thread safety fix in logging and SetLevel

https://github.com/op/go-logging/issues/104

When a logging is called concurrently with SetLevel, a panic occurs:
fatal error: concurrent map read and map write

goroutine 20 [running]:
runtime.throw(0x5f7cc0, 0x21)
	/home/yacovm/OBC/go/src/runtime/panic.go:530 +0x90 fp=0xc820038d58 sp=0xc820038d40
runtime.mapaccess2_faststr(0x551020, 0xc820078780, 0x5c9cc8, 0x4, 0x10, 0x551820)
	/home/yacovm/OBC/go/src/runtime/hashmap_fast.go:307 +0x5b fp=0xc820038db8 sp=0xc820038d58
_/home/yacovm/go-logging/go-logging.(*moduleLeveled).IsEnabledFor(0xc8200981e0, 0x4, 0x5c9cc8, 0x4, 0x0)
	/home/yacovm/go-logging/go-logging/level.go:110 +0x62 fp=0xc820038e18 sp=0xc820038db8
_/home/yacovm/go-logging/go-logging.(*Logger).IsEnabledFor(0xc8200788a0, 0x4, 0x0)
	/home/yacovm/go-logging/go-logging/logger.go:140 +0x4d fp=0xc820038e48 sp=0xc820038e18
_/home/yacovm/go-logging/go-logging.(*Logger).log(0xc8200788a0, 0x4, 0x0, 0xc8200d9b30, 0x1, 0x1)
	/home/yacovm/go-logging/go-logging/logger.go:144 +0x2f fp=0xc820038eb8 sp=0xc820038e48
_/home/yacovm/go-logging/go-logging.(*Logger).Info(0xc8200788a0, 0xc8200d9b30, 0x1, 0x1)
	/home/yacovm/go-logging/go-logging/logger.go:239 +0x51 fp=0xc820038ef0 sp=0xc820038eb8
_/home/yacovm/go-logging/go-logging.TestConcurrency(0xc8200a0120)
	/home/yacovm/go-logging/go-logging/logger_test.go:73 +0x11f fp=0xc820038f68 sp=0xc820038ef0
testing.tRunner(0xc8200a0120, 0x6b8468)

I added a RWLock to protect the map and added a regression test that many times
fails without the locks
---
 level.go       |  5 +++++
 logger_test.go | 14 ++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/level.go b/level.go
index 98dd191..5123f8e 100644
--- a/level.go
+++ b/level.go
@@ -66,6 +66,7 @@ type LeveledBackend interface {
 }
 
 type moduleLeveled struct {
+	sync.RWMutex
 	levels    map[string]Level
 	backend   Backend
 	formatter Formatter
@@ -88,6 +89,8 @@ func AddModuleLevel(backend Backend) LeveledBackend {
 
 // GetLevel returns the log level for the given module.
 func (l *moduleLeveled) GetLevel(module string) Level {
+	l.RLock()
+	defer l.RUnlock()
 	level, exists := l.levels[module]
 	if exists == false {
 		level, exists = l.levels[""]
@@ -101,6 +104,8 @@ func (l *moduleLeveled) GetLevel(module string) Level {
 
 // SetLevel sets the log level for the given module.
 func (l *moduleLeveled) SetLevel(level Level, module string) {
+	l.Lock()
+	defer l.Unlock()
 	l.levels[module] = level
 }
 
diff --git a/logger_test.go b/logger_test.go
index b9f7fe7..470e39b 100644
--- a/logger_test.go
+++ b/logger_test.go
@@ -60,3 +60,17 @@ func TestPrivateBackend(t *testing.T) {
 		t.Error("logged to defaultBackend:", MemoryRecordN(privateBackend, 0))
 	}
 }
+
+func TestConcurrency(t *testing.T) {
+	logger := MustGetLogger("test")
+	go func() {
+		for i := 0; i < 1000; i++ {
+			SetLevel(Level(DEBUG), "test")
+		}
+	}()
+
+	for i := 0; i < 1000; i++ {
+		logger.Info("")
+	}
+}
+