英文:
Why this code generate very big executable in go (around 81M)?
问题
我是你的中文翻译助手，以下是你提供的代码的翻译：
我对golang还不熟悉。我写了如下的代码：
package main
import (
"fmt"
)
const (
BIG_NUM = 10 * 1000 * 1000
)
type BigData [BIG_NUM]uint64
func (self BigData) String() string {
return fmt.Sprintf("%d\n", self[0])
}
func (self *BigData) Clear() {
*self = BigData{}
}
func main() {
data := new(BigData)
fmt.Println(data)
}
编译后，可执行文件大小约为81M：
$ ls -l
-rwxr-xr-x 1 tchen 522017917 81533376 Dec 19 08:44 test
-rw-r--r-- 1 tchen 522017917 290 Dec 19 08:44 test.go
当我移除Clear()函数时，可执行文件大小恢复正常。为什么Clear()函数会生成如此大的可执行文件？它应该在运行时调用，而不是编译时调用，对吗？
------------ 进一步调查 -----------
受@FUZxxl的启发，我修改了代码，在Clear()函数中使用了一个全局变量。这次文件大小恢复正常了。所以全局变量被正确地放置在.bss段中。
package main
import (
"fmt"
)
const (
BIG_NUM = 10 * 1000 * 1000
)
type BigData [BIG_NUM]uint64
var (
bigData = BigData{}
)
func (self BigData) String() string {
return fmt.Sprintf("%d\n", self[0])
}
func (self *BigData) Clear() {
*self = bigData
}
func main() {
data := new(BigData)
fmt.Println(data)
}
编译后的可执行文件：
$ ls -l
-rwxr-xr-x 1 tchen 522017917 1534384 Dec 19 10:55 test
-rw-r--r-- 1 tchen 522017917 318 Dec 19 10:55 test.go
------------ 最新更新 -----------
到目前为止，看起来这是一个编译器问题。已经提交了一个bug报告：https://code.google.com/p/go/issues/detail?id=6993。如果你感兴趣，可以跟进一下。
在找到解决方案之前，你应该避免在函数中使用x := Y{}的方式。一个解决方法是（感谢ality@pbrane.org）：
func (self *BigData) Clear() {
var zero BigData
*self = zero
}
英文:
I'm new to golang. I wrote code like this:
package main
import (
"fmt"
)
const (
BIG_NUM = 10 * 1000 * 1000
)
type BigData [BIG_NUM]uint64
func (self BigData) String() string {
return fmt.Sprintf("%d\n", self[0])
}
func (self *BigData) Clear() {
*self = BigData{}
}
func main() {
data := new(BigData)
fmt.Println(data)
}
After compiling, the executable is around 81M:
$ ls -l
-rwxr-xr-x 1 tchen 522017917 81533376 Dec 19 08:44 test
-rw-r--r-- 1 tchen 522017917 290 Dec 19 08:44 test.go
When I remove Clear() function, the executable goes to normal size. So why this Clear() function generate so big executable? It should be called at runtime, not compiling time, right?
------------ further investigation -----------
Enlightened by @FUZxxl, I modified the code to use a global variable in Clear(). This time the file size went back to normal. So global variables are putting to .bss section correctly.
package main
import (
"fmt"
)
const (
BIG_NUM = 10 * 1000 * 1000
)
type BigData [BIG_NUM]uint64
var (
bigData = BigData{}
)
func (self BigData) String() string {
return fmt.Sprintf("%d\n", self[0])
}
func (self *BigData) Clear() {
*self = bigData
}
func main() {
data := new(BigData)
fmt.Println(data)
}
The compiled executable:
$ ls -l
-rwxr-xr-x 1 tchen 522017917 1534384 Dec 19 10:55 test
-rw-r--r-- 1 tchen 522017917 318 Dec 19 10:55 test.go
------------ latest update -----------
So far it seems this is a compiler issue. A bug has been submitted: https://code.google.com/p/go/issues/detail?id=6993. You can follow up it if you're interested.
Before there's any solution to it, you should avoid using x := Y{} in your function. A workaround is (thanks to ality@pbrane.org):
func (self *BigData) Clear() {
- *self = BigData{}
+ var zero BigData
+ *self = zero
}
答案1
得分: 10
在Clear()函数中，BigData{}似乎导致一个大小为80,000,000字节的数组被硬编码到二进制文件中，其大小为sizeof uint64 * 10 * 1000 * 1000。
英文:
Looks like BigData{} in the Clear() function is causing an array of 80,000,000 bytes = sizeof uint64 * 10 * 1000 * 1000 to be hardcoded into the binary.
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