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1. 前言

在笔者的上一篇文章中，我们探讨了如何开发一个对业务无侵入的timeout middleware的实现，但是遗留了问题。在超时发生时，后台运行的子协程可能会不断累积，造成协程的泄露，最终引发程序奔溃。

2. 解决

为了解决子协程退出的问题，我们需要在超时发生时，通知子协程，让其也尽快退出。

下面的例子中，gin的处理函数long(c *gin.Context)中有对gRPC服务的调用 我们使用grpc/grpc-go 中提供的 greeter_server来提供gRPC服务

// Package main implements a server for Greeter service.
package main

import (
	"context"
	"log"
	"net"
    "time"
	"google.golang.org/grpc"
	pb "google.golang.org/grpc/examples/helloworld/helloworld"
)

const (
	port = ":50051"
)

// server is used to implement helloworld.GreeterServer.
type server struct{}

// SayHello implements helloworld.GreeterServer
func (s *server) SayHello(ctx context.Context, in *pb.HelloRequest) (*pb.HelloReply, error) {
	log.Printf("Received: %v", in.Name)
    time.Sleep(2*time.Second)
	return &pb.HelloReply{Message: "Hello " + in.Name}, nil
}

func main() {
	lis, err := net.Listen("tcp", port)
	if err != nil {
		log.Fatalf("failed to listen: %v", err)
	}
	s := grpc.NewServer()
	pb.RegisterGreeterServer(s, &server{})
	if err := s.Serve(lis); err != nil {
		log.Fatalf("failed to serve: %v", err)
	}
}

gin相关代码 main.go

package main

import (
	"bytes"
	"context"
	"github.com/gin-gonic/gin"
	"github.com/vearne/golib/buffpool"
	"google.golang.org/grpc"
	pb "google.golang.org/grpc/examples/helloworld/helloworld"
	"log"
	"net/http"
	"time"
)

const (
	address     = "localhost:50051"
	defaultName = "world"
)

type SimplebodyWriter struct {
	gin.ResponseWriter
	body *bytes.Buffer
}

func (w SimplebodyWriter) Write(b []byte) (int, error) {
	return w.body.Write(b)
}

func Timeout(t time.Duration) gin.HandlerFunc {
	return func(c *gin.Context) {
		// sync.Pool
		buffer := buffpool.GetBuff()

		blw := &SimplebodyWriter{body: buffer, ResponseWriter: c.Writer}
		c.Writer = blw

		// wrap the request context with a timeout
		ctx, cancel := context.WithTimeout(c.Request.Context(), t)
		c.Request = c.Request.WithContext(ctx)

		finish := make(chan struct{})
		// 子协程
		go func() {
			c.Next()
			finish <- struct{}{}
		}()

		select {
		case <-ctx.Done():
			c.Writer.WriteHeader(http.StatusGatewayTimeout)
			c.Abort()
			// 超时发生, 通知子协程退出
			cancel()
			// 如果超时的话，buffer无法主动清除，只能等待GC回收
		case <-finish:
			// 结果只会在主协程中被写入
			blw.ResponseWriter.Write(buffer.Bytes())
			buffpool.PutBuff(buffer)
		}
	}
}

func short(c *gin.Context) {
	time.Sleep(1 * time.Second)
	c.JSON(http.StatusOK, gin.H{"hello": "world"})
}

func long(c *gin.Context) {
    // RPC 调用
	// Set up a connection to the server.
	conn, err := grpc.Dial(address, grpc.WithInsecure())
	if err != nil {
		log.Fatalf("did not connect: %v", err)
	}
	defer conn.Close()
	greeter := pb.NewGreeterClient(conn)
	name := defaultName
	ctx := c.Request.Context()
	r, err := greeter.SayHello(ctx, &pb.HelloRequest{Name: name})
	if err != nil {
		log.Printf("could not greet: %v\n", err)
		return
	}
	log.Printf("Greeting: %s", r.Message)
	c.JSON(http.StatusOK, gin.H{"hello": "world"})
}

func main() {
	// create new gin without any middleware
	engine := gin.New()

	// add timeout middleware with 2 second duration
	engine.Use(Timeout(time.Second * 1))

	// create a handler that will last 1 seconds
	engine.GET("/short", short)

	// create a route that will last 5 seconds
	engine.GET("/long", long)

	// run the server
	log.Fatal(engine.Run(":8080"))
}

简单整理一下

╰─$ curl -v http://localhost:8080/long
*   Trying ::1...
* Connected to localhost (::1) port 8080 (#0)
> GET /long HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.46.0
> Accept: */*
>
< HTTP/1.1 504 Gateway Timeout
< Date: Thu, 16 May 2019 02:48:03 GMT
< Content-Length: 0
<
* Connection #0 to host localhost left intact

此时能够看到, gin server有超时异常提示，说明子协程确实退出了

[GIN-debug] GET    /short                    --> main.short (2 handlers)
[GIN-debug] GET    /long                     --> main.long (2 handlers)
[GIN-debug] Listening and serving HTTP on :8080
2019/05/20 23:16:45 could not greet: rpc error: code = DeadlineExceeded desc = context deadline exceeded

3. 后记

重要 此程序有bug，请阅读 GIN的TIMEOUT MIDDLEWARE实现(续2)

请我喝瓶饮料

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