From df1d8a392de61f9988b58dbec54d024752254129 Mon Sep 17 00:00:00 2001
From: Tevin Zhang <mail2tevin@gmail.com>
Date: Thu, 2 Jun 2016 11:47:41 +0800
Subject: [PATCH] Add CAS methods

---
 README.md    | 25 +++++++++++++++----------
 bool.go      | 13 +++++++++++++
 bool_test.go | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 60 insertions(+), 10 deletions(-)

diff --git a/README.md b/README.md
index 87dc2a7..3428a64 100644
--- a/README.md
+++ b/README.md
@@ -12,10 +12,11 @@ import "github.com/tevino/abool"
 
 cond := abool.New()  // default to false
 
-cond.Set()           // set to true
-cond.IsSet()         // returns true
-cond.UnSet()         // set to false
-cond.SetTo(true)     // set to whatever you want
+cond.Set()                 // Set to true
+cond.IsSet()               // Returns true
+cond.UnSet()               // Set to false
+cond.SetTo(true)           // Set to whatever you want
+cond.SetToIf(false, true)  // Set to true if it is false, returns false(not set)
 
 
 // embedding
@@ -31,13 +32,17 @@ type Foo struct {
 
 ```shell
 # Read
-BenchmarkMutexRead-4       	100000000	        21.1 ns/op
-BenchmarkAtomicValueRead-4 	200000000	         6.33 ns/op
-BenchmarkAtomicBoolRead-4  	300000000	         4.28 ns/op  # <--- This package
+BenchmarkMutexRead-4       	100000000	        21.0 ns/op
+BenchmarkAtomicValueRead-4 	200000000	         6.30 ns/op
+BenchmarkAtomicBoolRead-4  	300000000	         4.21 ns/op  # <--- This package
 
 # Write
-BenchmarkMutexWrite-4      	100000000	        21.7 ns/op
-BenchmarkAtomicValueWrite-4	 30000000	        47.8 ns/op
-BenchmarkAtomicBoolWrite-4 	200000000	         9.83 ns/op  # <--- This package
+BenchmarkMutexWrite-4      	100000000	        21.6 ns/op
+BenchmarkAtomicValueWrite-4	 30000000	        43.4 ns/op
+BenchmarkAtomicBoolWrite-4 	200000000	         9.87 ns/op  # <--- This package
+
+# CAS
+BenchmarkMutexCAS-4        	 30000000	        44.9 ns/op
+BenchmarkAtomicBoolCAS-4   	100000000	        11.7 ns/op   # <--- This package
 ```
 
diff --git a/bool.go b/bool.go
index 985d269..cbd9347 100644
--- a/bool.go
+++ b/bool.go
@@ -46,3 +46,16 @@ func (ab *AtomicBool) SetTo(yes bool) {
 		atomic.StoreInt32((*int32)(ab), 0)
 	}
 }
+
+// SetToIf sets the Boolean to new only if the Boolean matches the old
+// Returns whether the set was done
+func (ab *AtomicBool) SetToIf(old, new bool) (set bool) {
+	var o, n int32
+	if old {
+		o = 1
+	}
+	if new {
+		n = 1
+	}
+	return atomic.CompareAndSwapInt32((*int32)(ab), o, n)
+}
diff --git a/bool_test.go b/bool_test.go
index 81fd636..d63517f 100644
--- a/bool_test.go
+++ b/bool_test.go
@@ -41,6 +41,14 @@ func TestBool(t *testing.T) {
 	if v.IsSet() {
 		t.Fatal("AtomicBool.SetTo(false) failed")
 	}
+
+	if set := v.SetToIf(true, false); set || v.IsSet() {
+		t.Fatal("AtomicBool.SetTo(true, false) failed")
+	}
+
+	if set := v.SetToIf(false, true); !set || !v.IsSet() {
+		t.Fatal("AtomicBool.SetTo(false, true) failed")
+	}
 }
 
 func TestRace(t *testing.T) {
@@ -142,3 +150,27 @@ func BenchmarkAtomicBoolWrite(b *testing.B) {
 		v.Set()
 	}
 }
+
+// Benchmark CAS
+
+func BenchmarkMutexCAS(b *testing.B) {
+	var m sync.RWMutex
+	var v bool
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		m.Lock()
+		if !v {
+			v = true
+		}
+		m.Unlock()
+	}
+	b.StopTimer()
+}
+
+func BenchmarkAtomicBoolCAS(b *testing.B) {
+	v := New()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		v.SetToIf(false, true)
+	}
+}