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如何通过编程证明此代码具有竞争条件?

httpserver race-condition go

hendry · 技术社区 · 5 年前

func (h *handler) loggingMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        h.Log = log.WithFields(log.Fields{
            "method":     r.Method,
            "requestURI": r.RequestURI,
        })
        next.ServeHTTP(w, r)
    })
}

我试过了 go build -race ,然后运行二进制文件: PORT=3000 ./main hey -n 10000 -c 200 http://localhost:3000 .

下面是代码的其余部分: https://raw.githubusercontent.com/kaihendry/context-youtube/master/5/main.go

或

type handler struct{ Log *log.Entry }

func New() (h *handler) { return &handler{Log: log.WithFields(log.Fields{"test": "FAIL"})} }

func (h *handler) index(w http.ResponseWriter, r *http.Request) {
    h.Log.Info("index")
    fmt.Fprintf(w, "hello")
}

func (h *handler) about(w http.ResponseWriter, r *http.Request) {
    h.Log.Info("about")
    fmt.Fprintf(w, "about")
}

func main() {
    h := New()
    app := mux.NewRouter()
    app.HandleFunc("/", h.index)
    app.HandleFunc("/about", h.about)
    app.Use(h.loggingMiddleware)
    if err := http.ListenAndServe(":"+os.Getenv("PORT"), app); err != nil {
        log.WithError(err).Fatal("error listening")
    }
}

h.Log

2 回复 | 直到 5 年前

icza 5 年前

有一种编程方式,为此您必须做两件事:

重现活泼的状态
并使用 -race go 工具

最好是为它编写一个单元测试,这样测试也是可复制的,并且在每次构建/部署时自动运行/检查。

好的,那么如何复制它呢?

只需编写一个启动2个goroutine的测试,其中一个调用 index 处理程序,以及调用 about

使用 net/http/httptest httptest.NewServer() 给你一个准备就绪的服务器,用你传递给它的处理程序“武装”起来。

下面是一个简单的测试示例,它将触发竞争条件。把它放在一个名为 main_test.go ,在您的 main.go 文件:

package main

import (
    "fmt"
    "net/http"
    "net/http/httptest"
    "sync"
    "testing"

    "github.com/gorilla/mux"
)

func TestRace(t *testing.T) {
    h := New()
    app := mux.NewRouter()
    app.HandleFunc("/", h.index)
    app.HandleFunc("/about", h.about)
    app.Use(h.loggingMiddleware)

    server := httptest.NewServer(app)
    defer server.Close()

    wg := &sync.WaitGroup{}
    for _, path := range []string{"/", "/about"} {
        path := path
        wg.Add(1)
        go func() {
            defer wg.Done()
            req, err := http.NewRequest(http.MethodGet, server.URL+path, nil)
            fmt.Println(server.URL + path)
            if err != nil {
                panic(err)
            }
            res, err := http.DefaultClient.Do(req)
            if err != nil {
                panic(err)
            }
            defer res.Body.Close()
        }()
    }
    wg.Wait()
}

你必须用它来运行它

go test -race

示例输出为:

http://127.0.0.1:33007/
http://127.0.0.1:33007/about
==================
WARNING: DATA RACE
Write at 0x00c000098030 by goroutine 17:
  play.(*handler).loggingMiddleware.func1()
      /home/icza/tmp/gows/src/play/main.go:16 +0x1ce
  net/http.HandlerFunc.ServeHTTP()
      /usr/local/go/src/net/http/server.go:1964 +0x51
  github.com/gorilla/mux.(*Router).ServeHTTP()
      /home/icza/tmp/gows/src/github.com/gorilla/mux/mux.go:212 +0x12e
  net/http.serverHandler.ServeHTTP()
      /usr/local/go/src/net/http/server.go:2741 +0xc4
  net/http.(*conn).serve()
      /usr/local/go/src/net/http/server.go:1847 +0x80a

Previous write at 0x00c000098030 by goroutine 16:
  play.(*handler).loggingMiddleware.func1()
      /home/icza/tmp/gows/src/play/main.go:16 +0x1ce
  net/http.HandlerFunc.ServeHTTP()
      /usr/local/go/src/net/http/server.go:1964 +0x51
  github.com/gorilla/mux.(*Router).ServeHTTP()
      /home/icza/tmp/gows/src/github.com/gorilla/mux/mux.go:212 +0x12e
  net/http.serverHandler.ServeHTTP()
      /usr/local/go/src/net/http/server.go:2741 +0xc4
  net/http.(*conn).serve()
      /usr/local/go/src/net/http/server.go:1847 +0x80a

Goroutine 17 (running) created at:
  net/http.(*Server).Serve()
      /usr/local/go/src/net/http/server.go:2851 +0x4c5
  net/http/httptest.(*Server).goServe.func1()
      /usr/local/go/src/net/http/httptest/server.go:280 +0xac

Goroutine 16 (running) created at:
  net/http.(*Server).Serve()
      /usr/local/go/src/net/http/server.go:2851 +0x4c5
  net/http/httptest.(*Server).goServe.func1()
      /usr/local/go/src/net/http/httptest/server.go:280 +0xac
==================
2019/01/06 14:58:50  info index                     method=GET requestURI=/
2019/01/06 14:58:50  info about                     method=GET requestURI=/about
--- FAIL: TestRace (0.00s)
    testing.go:771: race detected during execution of test
FAIL
exit status 1
FAIL    play    0.011s

测试失败,表明存在数据竞争。

笔记:

与 sync.WaitGroup 是等待2个启动的goroutine,而不是同步对处理程序记录器的访问(这会导致数据争用)。如果您修复了数据争用,测试将正常运行并结束(等待2个启动的测试goroutine完成)。

David Maze 5 年前

假设您几乎在同一时间收到两个命中同一处理程序的入站连接。第一个连接开始运行:

h.Log = log.WithFields(log.Fields{
    "method":     rFirst.Method,
    "requestURI": rFirst.RequestURI,
})

但是等等!第二个连接出现了!也许运行时想要挂起这个goroutine并启动第二个连接。然后

h.Log = log.WithFields(log.Fields{
    "method":     rSecond.Method,
    "requestURI": rSecond.RequestURI,
})
next.ServeHTTP(wSecond, rSecond)

呸……这就完了。让我们回到我们的第一次狂欢。

// What's in h.Log now, with this sequence of events?
next.ServeHTTP(wFirst, rFirst)

第二组示例不会改变 h.Log ,但一定要对其调用方法。在大多数情况下,这可能安全,也可能不安全。这个 documentation for log.Logger "github.com/sirupsen/logrus" 像 log , that has a similar statement in its documentation

我可以假设设置h.Log是安全的吗?

没有 sync.Mutex The Go Memory Model 更精确地定义了什么样的副作用保证在出现时是可见的。