yangkunlun 2019-10-08
摘要: 总体上来说,HTTP每次请求比较浪费资源的。虽然HTTP也是走在TCP上面的,但是HTTP请求自己添加了很多自己的信息,因此会消耗带宽资源。所以一些公司就是用RPC作为内部应用的通信协议。原文
如果你对Go也感兴趣, 可以关注我的公众号: GoGuider
RPC(Remote Procedure Call,远程过程调用)是一种通过网络从远程计算机程序上请求服务,而不需要了解底层网络细节的应用程序通信协议。RPC协议构建于TCP或UDP,或者是HTTP上。
在Go中,标准库提供的net/rpc包实现了RPC协议需要的相关细节,开发者可以很方便的使用该包编写RPC的服务端和客户端程序。
从上图看, RPC本身就是一个client-server模型。
下面列举一个实例代码, 来了解RPC调用过程
package main import ( "fmt" "log" "net" "net/http" "net/rpc" "os" "time" ) type Args struct { A, B int } type Math int //计算乘积 func (t *Math) Multiply(args *Args, reply *int) error { time.Sleep(time.Second * 3) //睡1秒,同步调用会等待,异步会先往下执行 *reply = args.A * args.B fmt.Println("Multiply") return nil } //计算和 func (t *Math) Sum(args *Args, reply *int) error { time.Sleep(time.Second * 3) *reply = args.A + args.B fmt.Println("Sum") return nil } func main() { //创建对象 math := new(Math) //rpc服务注册了一个Math对象 公开方法供客户端调用 rpc.Register(math) //指定rpc的传输协议 这里采用http协议作为rpc调用的载体 也可以用rpc.ServeConn处理单个连接请求 rpc.HandleHTTP() l, e := net.Listen("tcp", ":1234") if e != nil { log.Fatal("listen error", e) } go http.Serve(l, nil) os.Stdin.Read(make([]byte, 1)) }
package main import ( "fmt" "log" "net/rpc" "time" ) type Args struct { A, B int } func main() { //调用rpc服务端提供的方法之前,先与rpc服务端建立连接 client, err := rpc.DialHTTP("tcp", "127.0.0.1:1234") if err != nil { log.Fatal("dialHttp error", err) return } //同步调用服务端提供的方法 args := &Args{7, 8} var reply int //可以查看源码 其实Call同步调用是用异步调用实现的。后续再详细学习 err = client.Call("Math.Multiply", args, &reply) //这里会阻塞三秒 if err != nil { log.Fatal("call Math.Multiply error", err) } fmt.Printf("Multiply:%d*%d=%d\n", args.A, args.B, reply) //异步调用 var sum int divCall := client.Go("Math.Sum", args, &sum, nil) //使用select模型监听通道有数据时执行,否则执行后续程序 for { select { case <-divCall.Done: fmt.Printf("%d+%d是%d, 退出执行!", args.A, args.B, sum) return default: fmt.Println("继续等待....") time.Sleep(time.Second * 1) } } }
go run server.go go run client.go
Multiply:7*8=56 继续等待.... 继续等待.... 继续等待.... 7+8=15,出执行
server端
client端
其实细心的朋友会注意到client.go 里面有client.Call 和 client.Go 调用;
查看源码可以看到client.Call 底层就是调用的client.Go
// 部分源码: / Go invokes the function asynchronously. It returns the Call structure representing // the invocation. The done channel will signal when the call is complete by returning // the same Call object. If done is nil, Go will allocate a new channel. // If non-nil, done must be buffered or Go will deliberately crash. func (client *Client) Go(serviceMethod string, args interface{}, reply interface{}, done chan *Call) *Call { call := new(Call) call.ServiceMethod = serviceMethod call.Args = args call.Reply = reply if done == nil { done = make(chan *Call, 10) // buffered. } else { // If caller passes done != nil, it must arrange that // done has enough buffer for the number of simultaneous // RPCs that will be using that channel. If the channel // is totally unbuffered, it's best not to run at all. if cap(done) == 0 { log.Panic("rpc: done channel is unbuffered") } } call.Done = done client.send(call) return call } // Call invokes the named function, waits for it to complete, and returns its error status. func (client *Client) Call(serviceMethod string, args interface{}, reply interface{}) error { call := <-client.Go(serviceMethod, args, reply, make(chan *Call, 1)).Done return call.Error }