此文中涉及的plugin运行环境为mac 10.14,go版本为1.11 主要是想讨论一下插件依赖的第三方库的问题. 例子是在https://github.com/vladimirvivien/go-plugin-example一文基础之上.
package main
import (
"fmt"
"os"
"plugin"
)
type Greeter interface {
Greet()
}
func main() {
// load module
// 1. open the so file to load the symbols
plug, err := plugin.Open("./eng/eng.so")
if err != nil {
fmt.Println(err)
os.Exit(1)
}
// 2. look up a symbol (an exported function or variable)
// in this case, variable Greeter
symGreeter, err := plug.Lookup("Greeter")
if err != nil {
fmt.Println(err)
os.Exit(1)
}
// 3. Assert that loaded symbol is of a desired type
// in this case interface type Greeter (defined above)
var greeter Greeter
greeter, ok := symGreeter.(Greeter)
if !ok {
fmt.Println("unexpected type from module symbol")
os.Exit(1)
}
// 4. use the module
greeter.Greet()
}
package main
import "fmt"
type greeting string
func (g greeting) Greet() {
fmt.Println("Hello Universe")
}
// exported
var Greeter greeting
go build -buildmode=plugin -o eng/eng.so eng/greeter.go
go run main.go
Hello Universe
如果主程序和插件都依赖第三方库会有什么问题呢?他们是共享一份代码?还是完全独立的copy呢? 这就类似于c语言动态链接库的依赖,但是应该又不一样. 以实验结果说话吧.
package anotherlib
var ShareVariable =7
和平时常见的动态库行为一致,也就是说主程序和插件共享了一份运行代码,也共享了一份运行变量.
实际项目中,可能代码都会使用vendor来管理自己的第三方依赖库. 这时候就会出现不一致的情况.也就是说因为主程序使用了vendor或者插件使用了vendor, 那么这时候go runtime就会认为插件和主程序用的不是同一个第三方依赖库,这时候就会出现和预期不一致的情况.
我已经把代码放在github,刚兴趣可以下载运行,
package main
import (
"fmt"
"os"
"plugin"
"github.com/nkbai/blog/goplugin/anotherlib"
)
type Greeter interface {
Greet()
GetShareVariable() int
}
func main() {
// load module
// 1. open the so file to load the symbols
plug, err := plugin.Open("./eng/eng.so")
if err != nil {
fmt.Println(err)
os.Exit(1)
}
// 2. look up a symbol (an exported function or variable)
// in this case, variable Greeter
symGreeter, err := plug.Lookup("Greeter")
if err != nil {
fmt.Println(err)
os.Exit(1)
}
// 3. Assert that loaded symbol is of a desired type
// in this case interface type Greeter (defined above)
var greeter Greeter
greeter, ok := symGreeter.(Greeter)
if !ok {
fmt.Println("unexpected type from module symbol")
os.Exit(1)
}
// 4. use the module
greeter.Greet()
fmt.Println("anotherlib in main")
fmt.Println(anotherlib.ShareVariable)
fmt.Printf("plugin anotherlib =%d\n",greeter.GetShareVariable())
fmt.Println("change anotherlib's variable")
anotherlib.ShareVariable=5
fmt.Printf("main share=%d,plugin share=%d\n",anotherlib.ShareVariable,greeter.GetShareVariable())
//可以看到输出都是5
//下面这种情况将会出现不一致的情况
testpluginvendor()
}
func testpluginvendor(){
// load module
// 1. open the so file to load the symbols
plug, err := plugin.Open("pluginwithvendor/eng.so")
if err != nil {
fmt.Println(err)
os.Exit(1)
}
// 2. look up a symbol (an exported function or variable)
// in this case, variable Greeter
symGreeter, err := plug.Lookup("Greeter")
if err != nil {
fmt.Println(err)
os.Exit(1)
}
// 3. Assert that loaded symbol is of a desired type
// in this case interface type Greeter (defined above)
var greeter Greeter
greeter, ok := symGreeter.(Greeter)
if !ok {
fmt.Println("unexpected type from module symbol")
os.Exit(1)
}
// 4. use the module
greeter.Greet()
fmt.Println("call plugin withvendor")
fmt.Println("anotherlib in main")
fmt.Println(anotherlib.ShareVariable)
fmt.Printf("plugin anotherlib =%d\n",greeter.GetShareVariable())
fmt.Println("change anotherlib's variable")
anotherlib.ShareVariable=5
fmt.Printf("main share=%d,plugin share=%d\n",anotherlib.ShareVariable,greeter.GetShareVariable())
//可以看到输出并不一致
}
package main
import "fmt"
import "github.com/nkbai/blog/goplugin/anotherlib"
type greeting string
func (g greeting) Greet() {
fmt.Println("Hello Universe")
}
func (g greeting) GetShareVariable() int{
return anotherlib.ShareVariable
}
// exported
var Greeter greeting
package anotherlib
var ShareVariable =7