From ca4cdfe4c0de07ac63889f8eb38f44e3cdc50a7b Mon Sep 17 00:00:00 2001
From: Bogdan Drutu <bogdandrutu@gmail.com>
Date: Fri, 16 Dec 2022 11:38:01 -0800
Subject: [PATCH] small contingency improvement in global error handler (#3543)

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>
---
 CHANGELOG.md    |  4 ++++
 handler.go      | 25 ++++++++++++-------------
 handler_test.go |  6 +++---
 3 files changed, 19 insertions(+), 16 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9f0e0943382..40dc1d752ab 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 - Add `Producer` interface and `Reader.RegisterProducer(Producer)` to `go.opentelemetry.io/otel/sdk/metric` to enable external metric Producers. (#3524)
 
+### Changed
+
+- Global error handler uses an atomic value instead of a mutex. (#3543)
+
 ## [1.11.2/0.34.0] 2022-12-05
 
 ### Added
diff --git a/handler.go b/handler.go
index 36cf09f7290..ecd363ab516 100644
--- a/handler.go
+++ b/handler.go
@@ -17,7 +17,8 @@ package otel // import "go.opentelemetry.io/otel"
 import (
 	"log"
 	"os"
-	"sync"
+	"sync/atomic"
+	"unsafe"
 )
 
 var (
@@ -34,28 +35,26 @@ var (
 )
 
 type delegator struct {
-	lock *sync.RWMutex
-	eh   ErrorHandler
+	delegate unsafe.Pointer
 }
 
 func (d *delegator) Handle(err error) {
-	d.lock.RLock()
-	defer d.lock.RUnlock()
-	d.eh.Handle(err)
+	d.getDelegate().Handle(err)
+}
+
+func (d *delegator) getDelegate() ErrorHandler {
+	return *(*ErrorHandler)(atomic.LoadPointer(&d.delegate))
 }
 
 // setDelegate sets the ErrorHandler delegate.
 func (d *delegator) setDelegate(eh ErrorHandler) {
-	d.lock.Lock()
-	defer d.lock.Unlock()
-	d.eh = eh
+	atomic.StorePointer(&d.delegate, unsafe.Pointer(&eh))
 }
 
 func defaultErrorHandler() *delegator {
-	return &delegator{
-		lock: &sync.RWMutex{},
-		eh:   &errLogger{l: log.New(os.Stderr, "", log.LstdFlags)},
-	}
+	d := &delegator{}
+	d.setDelegate(&errLogger{l: log.New(os.Stderr, "", log.LstdFlags)})
+	return d
 }
 
 // errLogger logs errors if no delegate is set, otherwise they are delegated.
diff --git a/handler_test.go b/handler_test.go
index 32906198f8c..b6b9b20cae0 100644
--- a/handler_test.go
+++ b/handler_test.go
@@ -54,7 +54,7 @@ type HandlerTestSuite struct {
 
 func (s *HandlerTestSuite) SetupSuite() {
 	s.errCatcher = new(testErrCatcher)
-	s.origHandler = globalErrorHandler.eh
+	s.origHandler = globalErrorHandler.getDelegate()
 
 	globalErrorHandler.setDelegate(&errLogger{l: log.New(s.errCatcher, "", 0)})
 }
@@ -111,12 +111,12 @@ func (s *HandlerTestSuite) TestAllowMultipleSets() {
 	secondary := &errLogger{l: log.New(notUsed, "", 0)}
 	SetErrorHandler(secondary)
 	s.Require().Same(GetErrorHandler(), globalErrorHandler, "set changed globalErrorHandler")
-	s.Require().Same(globalErrorHandler.eh, secondary, "new Handler not set")
+	s.Require().Same(globalErrorHandler.getDelegate(), secondary, "new Handler not set")
 
 	tertiary := &errLogger{l: log.New(notUsed, "", 0)}
 	SetErrorHandler(tertiary)
 	s.Require().Same(GetErrorHandler(), globalErrorHandler, "set changed globalErrorHandler")
-	s.Assert().Same(globalErrorHandler.eh, tertiary, "user Handler not overridden")
+	s.Assert().Same(globalErrorHandler.getDelegate(), tertiary, "user Handler not overridden")
 }
 
 func TestHandlerTestSuite(t *testing.T) {