Add: benchmark

strings/slice.go

@@ -3,8 +3,9 @@
 // governed by Apache License 2.0.
 
 // http://blog.csdn.net/siddontang/article/details/23541587
-// reflect.StringHeader和reflect.SliceHeader的结构体只相差末尾一个字段(cap)
-// vitess代码，一种很hack的做法，string和slice的转换只需要拷贝底层的指针，而不是内存拷贝。
+// the difference btw reflect.StringHeader and reflect.SliceHeader is that there is a 'cap' in reflect.SliceHeader.
+//
+// The following codes is from a vitness project.
 package gxstrings
 
 import (
@@ -12,6 +13,8 @@ import (
 	"unsafe"
 )
 
+// String converts slice to a string object just by convert its pointer type
+// on the same memory heap without copying.
 func String(b []byte) (s string) {
 	pbytes := (*reflect.SliceHeader)(unsafe.Pointer(&b))
 	pstring := (*reflect.StringHeader)(unsafe.Pointer(&s))
@@ -20,6 +23,8 @@ func String(b []byte) (s string) {
 	return
 }
 
+// String converts string to a slice object just by convert its pointer type
+// on the same memory heap without copying.
 func Slice(s string) (b []byte) {
 	pbytes := (*reflect.SliceHeader)(unsafe.Pointer(&b))
 	pstring := (*reflect.StringHeader)(unsafe.Pointer(&s))
@@ -40,4 +45,3 @@ func BytePointer(b []byte) unsafe.Pointer {
 	p := (*reflect.SliceHeader)(unsafe.Pointer(&b))
 	return unsafe.Pointer(p.Data)
 }
-

strings/slice_test.go

 package gxstrings
 
 import (
+	"reflect"
 	"testing"
 )
 
 // go test  -v slice_test.go  slice.go
 
-// slice转string之后，如果slice的值有变化，string也会跟着改变
 func TestString(t *testing.T) {
 	b := []byte("hello world")
+	// After converting slice to string, the string value will change
+	// when the slice got new value.
 	a := String(b)
 	b[0] = 'a'
-	println(a) //output  aello world
+	if !reflect.DeepEqual("aello world", a) {
+		t.Errorf("a:%+v != `aello world`", a)
+	}
 }
 
-func TestSlice(t *testing.T) {
-	// 编译器会把 "hello, world" 这个字符串常量的字节数组分配在没有写权限的 memory segment
-	a := "hello world"
-	b := Slice(a)
-
-	// !!! 上面这个崩溃在defer里面是recover不回来的，真的就崩溃了，原因可能就跟c的非法内存访问一样，os不跟你玩了
-	// b[0] = 'a' //这里就等着崩溃吧
+// BenchmarkString0-8   	2000000000	         0.27 ns/op
+func BenchmarkString0(b *testing.B) {
+	b.StartTimer()
+	for i := 0; i < 100000000; i++ {
+		bs := []byte("hello world")
+		_ = string(bs)
+		bs[0] = 'a'
+	}
+	b.StopTimer()
+	bs := []byte("hello world")
+	a := string(bs)
+	bs[0] = 'a'
+	if reflect.DeepEqual("aello world", a) {
+		b.Errorf("a:%+v != `aello world`", a)
+	}
+}
 
-	//但是可以这样，因为go又重新给b分配了内存
-	b = append(b, "hello world"...)
-	println(String(b)) // output: hello worldhello world
+// BenchmarkString-8   	       1	1722255064 ns/op
+func BenchmarkString(b *testing.B) {
+	b.StartTimer()
+	for i := 0; i < 100000000; i++ {
+		bs := []byte("hello world")
+		_ = String(bs)
+		bs[0] = 'a'
+	}
+	b.StopTimer()
+	bs := []byte("hello world")
+	a := String(bs)
+	bs[0] = 'a'
+	if !reflect.DeepEqual("aello world", a) {
+		b.Errorf("a:%+v != `aello world`", a)
+	}
 }
 
-func TestSlice2(t *testing.T) {
-	// 你可以动态生成一个字符串，使其分配在可写的区域，比如 gc heap，那么就不会崩溃了。
+func TestSlice(t *testing.T) {
 	a := string([]byte("hello world"))
 	b := Slice(a)
 	b = append(b, "hello world"...)
-	println(String(b)) // output: hello worldhello world
+	println(String(b))
+
+	if !reflect.DeepEqual([]byte("hello worldhello world"), b) {
+		t.Errorf("a:%+v != `hello worldhello world`", string(b))
+	}
 }
 
+// BenchmarkSlice0-8   	       1	1187713598 ns/op
+func BenchmarkSlice0(b *testing.B) {
+	for i := 0; i < 100000000; i++ {
+		a := string([]byte("hello world"))
+		bs := ([]byte)(a)
+		_ = append(bs, "hello world"...)
+	}
+}
+
+// BenchmarkSlice-8   	       1	4895001383 ns/op
+func BenchmarkSlice(b *testing.B) {
+	for i := 0; i < 100000000; i++ {
+		a := string([]byte("hello world"))
+		bs := Slice(a)
+		_ = append(bs, "hello world"...)
+	}
+}