mirror of
https://github.com/unknwon/the-way-to-go_ZH_CN.git
synced 2025-08-12 03:06:41 +08:00
14.10 Multiplexing 复用 (#626)
* Create 14.10.md * Update 14.10.md * 这一句不知道怎么翻了 > Continuing with the simple form,the server could launch for each request a function run() in a goroutine that will apply an operation op of type binOp to the ints and then send the result on the reply channel: Continuing with the simple form,服务器会为每一个请求启动一个协程并在其中执行`run()`函数，此举会将类型为`binOp`的`op`操作返回的int值发送到`replyc`通道。 * Update 14.10.md * Update 14.10.md * Update 14.10.md
This commit is contained in:
Respawnz
ᴊ. ᴄʜᴇɴ
264
eBook/14.10.md
Normal file
264
eBook/14.10.md
Normal file
@@ -0,0 +1,264 @@
|
||||
# 14.10 复用
|
||||
|
||||
## 14.10.1 典型的客户端/服务器（C/S）模式
|
||||
|
||||
客户端-服务器应用正是 goroutines 和 channels 的亮点所在。
|
||||
|
||||
客户端(Client)可以是运行在任意设备上的任意程序，它会按需发送请求(request)至服务器。服务器(Server)接收到这个请求后开始相应的工作，然后再将响应(response)返回给客户端。典型情况下一般是多个客户端（既多个请求）对应一个（或少量）服务器。例如我们日常使用的浏览器客户端，其功能就是向服务器请求网页。而Web服务器则会向浏览器响应网页数据。
|
||||
|
||||
使用Go的服务器通常会在协程中执行向客户端的响应，故而会对每一个客户端请求启动一个协程。一个常用的操作方法是客户端请求自身中包含一个通道，而服务器则向这个通道发送响应。
|
||||
|
||||
例如下面这个`Request`结构，其中内嵌了一个`replyc`通道。
|
||||
```go
|
||||
type Request struct {
|
||||
a, b int
|
||||
replyc chan int // reply channel inside the Request
|
||||
}
|
||||
```
|
||||
或者更通俗的：
|
||||
```go
|
||||
type Reply struct{...}
|
||||
type Request struct{
|
||||
arg1, arg2, arg3 some_type
|
||||
replyc chan *Reply
|
||||
}
|
||||
```
|
||||
|
||||
|
||||
接下来先使用简单的形式,服务器会为每一个请求启动一个协程并在其中执行`run()`函数，此举会将类型为`binOp`的`op`操作返回的int值发送到`replyc`通道。
|
||||
|
||||
|
||||
```go
|
||||
type binOp func(a, b int) int
|
||||
|
||||
func run(op binOp, req *Request) {
|
||||
req.replyc <- op(req.a, req.b)
|
||||
}
|
||||
```
|
||||
`server`协程会无限循环以从`chan \*Request`接收请求，并且为了避免被长时间操作所堵塞，它将为每一个请求启动一个协程来做具体的工作：
|
||||
|
||||
```go
|
||||
func server(op binOp, service chan *Request) {
|
||||
for {
|
||||
req := <-service; // requests arrive here
|
||||
// start goroutine for request:
|
||||
go run(op, req); // don’t wait for op to complete
|
||||
}
|
||||
}
|
||||
```
|
||||
`server`本身则是以协程的方式在`startServer`函数中启动：
|
||||
```go
|
||||
func startServer(op binOp) chan *Request {
|
||||
reqChan := make(chan *Request);
|
||||
go server(op, reqChan);
|
||||
return reqChan;
|
||||
}
|
||||
```
|
||||
`startServer`则会在`main`协程中被调用。
|
||||
|
||||
在以下测试例子中，100个请求会被发送到服务器，只有它们全部被送达后我们才会按相反的顺序检查响应：
|
||||
```go
|
||||
func main() {
|
||||
adder := startServer(func(a, b int) int { return a + b })
|
||||
const N = 100
|
||||
var reqs [N]Request
|
||||
for i := 0; i < N; i++ {
|
||||
req := &reqs[i]
|
||||
req.a = i
|
||||
req.b = i + N
|
||||
req.replyc = make(chan int)
|
||||
adder <- req // adder is a channel of requests
|
||||
}
|
||||
// checks:
|
||||
for i := N - 1; i >= 0; i-- {
|
||||
// doesn’t matter what order
|
||||
if <-reqs[i].replyc != N+2*i {
|
||||
fmt.Println(“fail at”, i)
|
||||
} else {
|
||||
fmt.Println(“Request “, i, “is ok!”)
|
||||
}
|
||||
}
|
||||
fmt.Println(“done”)
|
||||
}
|
||||
```
|
||||
这些代码可以在[multiplex_server.go](examples/chapter_14/multiplex_server.go)找到
|
||||
|
||||
输出：
|
||||
|
||||
Request 99 is ok!
|
||||
Request 98 is ok!
|
||||
...
|
||||
Request 1 is ok!
|
||||
Request 0 is ok!
|
||||
done
|
||||
|
||||
|
||||
这个程序仅启动了100个协程。然而即使执行100,000个协程我们也能在数秒内看到它完成。这说明了Go的协程是如何的轻量：如果我们启动相同数量的真实的线程，程序早就崩溃了。
|
||||
|
||||
示例： [14.14-multiplex_server.go](examples/chapter_14/multiplex_server.go)
|
||||
```go
|
||||
package main
|
||||
|
||||
import "fmt"
|
||||
|
||||
type Request struct {
|
||||
a, b int
|
||||
replyc chan int // reply channel inside the Request
|
||||
}
|
||||
|
||||
type binOp func(a, b int) int
|
||||
|
||||
func run(op binOp, req *Request) {
|
||||
req.replyc <- op(req.a, req.b)
|
||||
}
|
||||
|
||||
func server(op binOp, service chan *Request, quit chan bool) {
|
||||
for {
|
||||
select {
|
||||
case req := <-service:
|
||||
go run(op, req)
|
||||
case <-quit:
|
||||
return
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
func startServer(op binOp) (service chan *Request, quit chan bool) {
|
||||
service = make(chan *Request)
|
||||
quit = make(chan bool)
|
||||
go server(op, service, quit)
|
||||
return service, quit
|
||||
}
|
||||
|
||||
func main() {
|
||||
adder, quit := startServer(func(a, b int) int { return a + b })
|
||||
const N = 100
|
||||
var reqs [N]Request
|
||||
for i := 0; i < N; i++ {
|
||||
req := &reqs[i]
|
||||
req.a = i
|
||||
req.b = i + N
|
||||
req.replyc = make(chan int)
|
||||
adder <- req
|
||||
}
|
||||
// checks:
|
||||
for i := N - 1; i >= 0; i-- { // doesn't matter what order
|
||||
if <-reqs[i].replyc != N+2*i {
|
||||
fmt.Println("fail at", i)
|
||||
} else {
|
||||
fmt.Println("Request ", i, " is ok!")
|
||||
}
|
||||
}
|
||||
quit <- true
|
||||
fmt.Println("done")
|
||||
}
|
||||
```
|
||||
## 14.10.2 卸载（Teardown）：通过信号通道关闭服务器
|
||||
|
||||
在上一个版本中`server`在`main`函数返回后并没有完全关闭，而被强制结束了。为了改进这一点，我们可以提供一个退出通道给`server`：
|
||||
|
||||
```go
|
||||
func startServer(op binOp) (service chan *Request, quit chan bool) {
|
||||
service = make(chan *Request)
|
||||
quit = make(chan bool)
|
||||
go server(op, service, quit)
|
||||
return service, quit
|
||||
}
|
||||
```
|
||||
|
||||
`server`函数现在则使用`select`在`service`通道和`quit`通道之间做出选择：
|
||||
|
||||
```go
|
||||
func server(op binOp, service chan *request, quit chan bool) {
|
||||
for {
|
||||
select {
|
||||
case req := <-service:
|
||||
go run(op, req)
|
||||
case <-quit:
|
||||
return
|
||||
}
|
||||
}
|
||||
}
|
||||
```
|
||||
当`quit`通道接收到一个`true`值时，`server`就会返回并结束。
|
||||
|
||||
在`main`函数中我们做出如下更改：
|
||||
|
||||
adder, quit := startServer(func(a, b int) int { return a + b })
|
||||
|
||||
在`main`函数的结尾处我们放入这一行：`quit <- true`
|
||||
|
||||
完整的代码在 multiplex_server2.go,输出和上一个版本是一样的。
|
||||
|
||||
示例： [14.15-multiplex_server2.go](examples/chapter_14/multiplex_server2.go)
|
||||
```go
|
||||
package main
|
||||
|
||||
import "fmt"
|
||||
|
||||
type Request struct {
|
||||
a, b int
|
||||
replyc chan int // reply channel inside the Request
|
||||
}
|
||||
|
||||
type binOp func(a, b int) int
|
||||
|
||||
func run(op binOp, req *Request) {
|
||||
req.replyc <- op(req.a, req.b)
|
||||
}
|
||||
|
||||
func server(op binOp, service chan *Request, quit chan bool) {
|
||||
for {
|
||||
select {
|
||||
case req := <-service:
|
||||
go run(op, req)
|
||||
case <-quit:
|
||||
return
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
func startServer(op binOp) (service chan *Request, quit chan bool) {
|
||||
service = make(chan *Request)
|
||||
quit = make(chan bool)
|
||||
go server(op, service, quit)
|
||||
return service, quit
|
||||
}
|
||||
|
||||
func main() {
|
||||
adder, quit := startServer(func(a, b int) int { return a + b })
|
||||
const N = 100
|
||||
var reqs [N]Request
|
||||
for i := 0; i < N; i++ {
|
||||
req := &reqs[i]
|
||||
req.a = i
|
||||
req.b = i + N
|
||||
req.replyc = make(chan int)
|
||||
adder <- req
|
||||
}
|
||||
// checks:
|
||||
for i := N - 1; i >= 0; i-- { // doesn't matter what order
|
||||
if <-reqs[i].replyc != N+2*i {
|
||||
fmt.Println("fail at", i)
|
||||
} else {
|
||||
fmt.Println("Request ", i, " is ok!")
|
||||
}
|
||||
}
|
||||
quit <- true
|
||||
fmt.Println("done")
|
||||
}
|
||||
```
|
||||
练习 [14.13 multiplex_server3.go](exercises/chapter_14/multiplex_server3.go):使用之前的例子，编写一个在`Request`结构上带有`String()`方法的版本，它能决定服务器如何输出；并使用以下两个请求来测试这个程序：
|
||||
```go
|
||||
req1 := &Request{3, 4, make(chan int)}
|
||||
req2 := &Request{150, 250, make(chan int)}
|
||||
...
|
||||
// show the output
|
||||
fmt.Println(req1,"\n",req2)
|
||||
```
|
||||
|
||||
## 链接
|
||||
|
||||
- [目录](directory.md)
|
||||
- 上一节：[实现 Futures 模式](14.9.md)
|
||||
- 下一节：[限制同时处理的请求数](14.11.md)
|
||||
Reference in New Issue
Block a user