Go 如何通过编程证明此代码具有竞争条件?
我被告知这段代码有一个设计上的竞争条件,尽管我可能会尝试,但我无法证明它有竞争条件Go 如何通过编程证明此代码具有竞争条件?,go,race-condition,httpserver,Go,Race Condition,Httpserver,我被告知这段代码有一个设计上的竞争条件,尽管我可能会尝试,但我无法证明它有竞争条件 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"
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)
})
}
我尝试了go build-race
,然后运行二进制代码:PORT=3000./main
&加载像hey-n 10000-c 200这样的创建者http://localhost:3000
下面是代码的其余部分:
或
如果我不能证明它有竞争条件,我可以假设设置
h.Log
是安全的吗?想象一下,您在几乎相同的时间收到两个到达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)
或者
您的第二组示例不会更改h.Log
的值,但会对其调用方法。在大多数情况下,这可能安全,也可能不安全。包含神奇的短语:“可以从多个goroutine同时使用记录器”。(如果您实际导入了“github.com/sirupsen/logrus”
作为log
,)
我可以假设设置h.Log是安全的吗
没有一个
sync.Mutex
或类似的东西来保护它,不是真的。您肯定不能保证,如果您在第1行设置它,那么如果其他goroutine可能正在更改它,它在第2行将具有相同的值。有一个更精确的定义,即什么样的副作用保证在出现时是可见的。有一种编程方式,您必须做两件事:
- 重现活泼的状态
- 并在启动
工具时使用go
选项-race
索引
处理程序,另一个调用关于
处理程序,故意不同步,这就是触发竞争检测器的原因
使用该包可以轻松地测试处理程序。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。将它放在名为main\u test.go
的文件中,在main.go
文件旁边:
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
注意事项:
与
sync.WaitGroup
的同步是等待2个已启动的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)。您有一个处理程序实例h
,该处理程序在每次请求时都会重新分配相同的日志
字段。通过并发请求获得竞争非常简单。是的,但我想知道如何以编程方式确认这一点,而无需太多推理。如果你尝试并发写入,go race检测器会捕捉到这一点。如果您的测试没有以正确的方式执行此代码,您可能永远也检测不到它。尽管我以并发方式使用iiuc。那我还能怎么测试。。。以正确的方式?以编程方式检测竞争条件类似于解决停止问题,无法静态地保证可以达到特定的状态。因此,没有编程方式确定它是否具有竞争条件?哇,太棒了,谢谢。我已将你的答案添加到
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