From bb9a8edc0f888f7dcda2e967c3409846a9d8475c Mon Sep 17 00:00:00 2001
From: alexeypavlenko <alex.gripav@gmail.com>
Date: Thu, 27 Sep 2018 19:07:59 +0300
Subject: [PATCH] Introduce an atomic type-safe wrapper around error type.
 (#42)

---
 error.go       | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++
 error_test.go  | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++
 stress_test.go | 16 +++++++++++++++
 3 files changed, 126 insertions(+)
 create mode 100644 error.go
 create mode 100644 error_test.go

diff --git a/error.go b/error.go
new file mode 100644
index 0000000..0489d19
--- /dev/null
+++ b/error.go
@@ -0,0 +1,55 @@
+// Copyright (c) 2016 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package atomic
+
+// Error is an atomic type-safe wrapper around Value for errors
+type Error struct{ v Value }
+
+// errorHolder is non-nil holder for error object.
+// atomic.Value panics on saving nil object, so err object needs to be
+// wrapped with valid object first.
+type errorHolder struct{ err error }
+
+// NewError creates new atomic error object
+func NewError(err error) *Error {
+	e := &Error{}
+	if err != nil {
+		e.Store(err)
+	}
+	return e
+}
+
+// Load atomically loads the wrapped error
+func (e *Error) Load() error {
+	v := e.v.Load()
+	if v == nil {
+		return nil
+	}
+
+	eh := v.(errorHolder)
+	return eh.err
+}
+
+// Store atomically stores error.
+// NOTE: a holder object is allocated on each Store call.
+func (e *Error) Store(err error) {
+	e.v.Store(errorHolder{err: err})
+}
diff --git a/error_test.go b/error_test.go
new file mode 100644
index 0000000..cab2e7d
--- /dev/null
+++ b/error_test.go
@@ -0,0 +1,55 @@
+// Copyright (c) 2016 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package atomic
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestErrorByValue(t *testing.T) {
+	err := &Error{}
+	require.Nil(t, err.Load(), "Initial value shall be nil")
+}
+
+func TestNewErrorWithNilArgument(t *testing.T) {
+	err := NewError(nil)
+	require.Nil(t, err.Load(), "Initial value shall be nil")
+}
+
+func TestErrorCanStoreNil(t *testing.T) {
+	err := NewError(errors.New("hello"))
+	err.Store(nil)
+	require.Nil(t, err.Load(), "Stored value shall be nil")
+}
+
+func TestNewErrorWithError(t *testing.T) {
+	err1 := errors.New("hello1")
+	err2 := errors.New("hello2")
+
+	atom := NewError(err1)
+	require.Equal(t, err1, atom.Load(), "Expected Load to return initialized value")
+
+	atom.Store(err2)
+	require.Equal(t, err2, atom.Load(), "Expected Load to return overridden value")
+}
diff --git a/stress_test.go b/stress_test.go
index 8fd1251..3dc7852 100644
--- a/stress_test.go
+++ b/stress_test.go
@@ -21,6 +21,7 @@
 package atomic
 
 import (
+	"errors"
 	"math"
 	"runtime"
 	"sync"
@@ -46,6 +47,7 @@ var _stressTests = map[string]func() func(){
 	"bool":     stressBool,
 	"string":   stressString,
 	"duration": stressDuration,
+	"error":    stressError,
 }
 
 func TestStress(t *testing.T) {
@@ -256,3 +258,17 @@ func stressDuration() func() {
 		atom.Store(1)
 	}
 }
+
+func stressError() func() {
+	var atom = NewError(nil)
+	var err1 = errors.New("err1")
+	var err2 = errors.New("err2")
+	return func() {
+		atom.Load()
+		atom.Store(err1)
+		atom.Load()
+		atom.Store(err2)
+		atom.Load()
+		atom.Store(nil)
+	}
+}