无互斥量的Go例程

Question

尽管在写入共享资源时运行我的goroutine时没有任何互斥体，但是我没有遇到任何预期的运行时错误。相反，我得到了这个输出。 goroutine正在覆盖共享资源的输出未打印。但是，当我使用go run .运行时，我可以看到运行时错误。为什么会这样？

编辑：我注意到如果生成可执行文件然后运行它，我不会得到运行时错误。但是如果我使用go run .，我会得到它们。

GOROOT=C:\Go #gosetup
GOPATH=C:\Users\vtimo\go #gosetup
C:\Go\bin\go.exe build -i -o C:\Users\vtimo\Projects\go-concurrency\src\go_build_main_go_book_go.exe C:\Users\vtimo\Projects\go-concurrency\main.go C:\Users\vtimo\Projects\go-concurrency\book.go #gosetup
C:\Users\vtimo\Projects\go-concurrency\src\go_build_main_go_book_go.exe #gosetup
from database
from database
Title:          "The Android's Dream"
Author:         "John Scalzi"
Published:      2006

from database
Title:          "The Hobbit"
Author:         "J.R.R. Tolkien"
Published:      1937

from database
Title:          "On Basilisk Station"
Author:         "David Weber"
Published:      1993

from database
Title:          "The Hobbit"
Author:         "J.R.R. Tolkien"
Published:      1937

from database
Title:          "On Basilisk Station"
Author:         "David Weber"
Published:      1993

from database
Title:          "The Gods Themselves"
Author:         "Isaac Asimov"
Published:      1973

from database
Title:          "A Tale of Two Cities"
Author:         "Charles Dickens"
Published:      1859

Title:          "The Gods Themselves"
Author:         "Isaac Asimov"
Published:      1973

from database
Title:          "I, Robot"
Author:         "Isaac Asimov"
Published:      1950

from database
Title:          "The Hitchhiker's Guide to the Galaxy"
Author:         "Douglas Adams"
Published:      1979


Process finished with exit code 0

源代码：

package main

import (
    "fmt"
    "math/rand"
    "sync"
    "time"
)

var cache = map[int]Book{}
var rnd = rand.New(rand.NewSource(time.Now().UnixNano()))

func main() {
    wg := &sync.WaitGroup{}
    for i := 0; i < 10; i++ {
        id := rnd.Intn(10) + 1
        wg.Add(2)
        go func(id int, group *sync.WaitGroup) {
            if b, ok := queryCache(id); ok {
                fmt.Println("from cache")
                fmt.Println(b)
            }
            wg.Done()
        }(id, wg)
        go func(id int, group *sync.WaitGroup) {
            if b, ok := queryDatabase(id); ok {
                fmt.Println("from database")
                fmt.Println(b)
            }
            wg.Done()
        }(id, wg)


    }
    wg.Wait()
}

func queryCache(id int) (Book, bool) {
    b, ok := cache[id]
    return b, ok
}

func queryDatabase(id int) (Book, bool) {
    time.Sleep(100 * time.Millisecond)
    for _, b := range books {
        if b.ID == id {
            cache[id] = b
            return b, true
        }
    }
    return Book{}, false
}

Answer 1

您可以使用-race标志来检查是否存在任何竞争情况：

示例：go run -race programfile.go