From 762af9dda26238f09c0236acaf7daf07d7961e8b Mon Sep 17 00:00:00 2001
From: Changkun Ou <hi@changkun.us>
Date: Fri, 18 Sep 2020 16:45:01 +0200
Subject: [PATCH] optimize AtomicError (#82)
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This commit optimize AtomicError using atomic.Value. Benchmarks:

name               old time/op  new time/op  delta
AtomicError/Load-6   305ns ±11%    12ns ± 6%  -96.18%  (p=0.000 n=10+10)
AtomicError/Set-6   314ns ±16%    14ns ± 2%  -95.61%  (p=0.000 n=10+9)
---
 core/errorx/atomicerror.go      | 17 +++++------
 core/errorx/atomicerror_test.go | 52 +++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+), 10 deletions(-)

diff --git a/core/errorx/atomicerror.go b/core/errorx/atomicerror.go
index 76f874e5..d885f489 100644
--- a/core/errorx/atomicerror.go
+++ b/core/errorx/atomicerror.go
@@ -1,21 +1,18 @@
 package errorx
 
-import "sync"
+import "sync/atomic"
 
 type AtomicError struct {
-	err  error
-	lock sync.Mutex
+	err atomic.Value // error
 }
 
 func (ae *AtomicError) Set(err error) {
-	ae.lock.Lock()
-	ae.err = err
-	ae.lock.Unlock()
+	ae.err.Store(err)
 }
 
 func (ae *AtomicError) Load() error {
-	ae.lock.Lock()
-	err := ae.err
-	ae.lock.Unlock()
-	return err
+	if v := ae.err.Load(); v != nil {
+		return v.(error)
+	}
+	return nil
 }
diff --git a/core/errorx/atomicerror_test.go b/core/errorx/atomicerror_test.go
index fa19cdb2..d05f8866 100644
--- a/core/errorx/atomicerror_test.go
+++ b/core/errorx/atomicerror_test.go
@@ -2,6 +2,8 @@ package errorx
 
 import (
 	"errors"
+	"sync"
+	"sync/atomic"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -19,3 +21,53 @@ func TestAtomicErrorNil(t *testing.T) {
 	var err AtomicError
 	assert.Nil(t, err.Load())
 }
+
+func BenchmarkAtomicError(b *testing.B) {
+	var aerr AtomicError
+	wg := sync.WaitGroup{}
+
+	b.Run("Load", func(b *testing.B) {
+		var done uint32
+		go func() {
+			for {
+				if atomic.LoadUint32(&done) != 0 {
+					break
+				}
+				wg.Add(1)
+				go func() {
+					aerr.Set(errDummy)
+					wg.Done()
+				}()
+			}
+		}()
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			_ = aerr.Load()
+		}
+		b.StopTimer()
+		atomic.StoreUint32(&done, 1)
+		wg.Wait()
+	})
+	b.Run("Set", func(b *testing.B) {
+		var done uint32
+		go func() {
+			for {
+				if atomic.LoadUint32(&done) != 0 {
+					break
+				}
+				wg.Add(1)
+				go func() {
+					_ = aerr.Load()
+					wg.Done()
+				}()
+			}
+		}()
+		b.ResetTimer()
+		for i := 0; i < b.N; i++ {
+			aerr.Set(errDummy)
+		}
+		b.StopTimer()
+		atomic.StoreUint32(&done, 1)
+		wg.Wait()
+	})
+}