python - 运行 Go 异步操作并写入 map

Question

我有this project试图在 Go 中同时运行无限制的大查询。父项目都是 Python。我需要能够跟踪查询结果，就像在 map 中一样。

Input:

{
 'reports_portal': 'select * from reports_portal',
 'billing_portal': 'select * from billing_portal',
}

output:

{
 'reports_portal': [23, 123, 5234, 632],
 'billing_portal': [23, 123, 5234, 632],
}

等等

这些大查询需要异步运行，因为它们非常慢(从 UI 的角度来看，SRE 需要等待 15-30 秒才能获得结果。

我首先尝试将项目异步写入 map :

package main

import (
    "fmt"
)


func add_to_map(m map[string] string, word string) map[string]string {
    added_word := word + " plus more letters"
    m[word] = added_word
    return m
}


func main() {
    words_map := make(map[string]string)
    words := []string{"giraffe", "cat", "dog", "turtle"}
    for _, this_word := range words {
        go add_to_map(words_map, this_word)
    }
    fmt.Println(words_map)
}

爆炸像:

$ go run try_asynchronous.go 
fatal error: concurrent map writes

goroutine 7 [running]:
runtime.throw(0x10b3b96, 0x15)
    /usr/local/Cellar/go/1.8.1/libexec/src/runtime/panic.go:596 +0x95 fp=0xc420032eb8 sp=0xc420032e98
runtime.mapassign(0x109ad20, 0xc420016270, 0xc420032fa0, 0x10b3268)
    /usr/local/Cellar/go/1.8.1/libexec/src/runtime/hashmap.go:499 +0x667 fp=0xc420032f58 sp=0xc420032eb8
main.add_to_map(0xc420016270, 0x10b1ba0, 0x3, 0x0)
    /tmp/golang-w-python/try_asynchronous.go:10 +0xa3 fp=0xc420032fc0 sp=0xc420032f58
runtime.goexit()
    /usr/local/Cellar/go/1.8.1/libexec/src/runtime/asm_amd64.s:2197 +0x1 fp=0xc420032fc8 sp=0xc420032fc0
created by main.main
    /tmp/golang-w-python/try_asynchronous.go:19 +0xc8

goroutine 1 [runnable]:
fmt.(*pp).fmtString(0xc42001e0c0, 0x10b1f52, 0x7, 0x76)
    /usr/local/Cellar/go/1.8.1/libexec/src/fmt/print.go:424 +0x1a2
fmt.(*pp).printValue(0xc42001e0c0, 0x10953c0, 0xc42000e260, 0x98, 0x76, 0x1)
    /usr/local/Cellar/go/1.8.1/libexec/src/fmt/print.go:729 +0x27aa
fmt.(*pp).printValue(0xc42001e0c0, 0x109ad20, 0xc420016270, 0x15, 0x76, 0x0)
    /usr/local/Cellar/go/1.8.1/libexec/src/fmt/print.go:750 +0x103d
fmt.(*pp).printArg(0xc42001e0c0, 0x109ad20, 0xc420016270, 0x76)
    /usr/local/Cellar/go/1.8.1/libexec/src/fmt/print.go:682 +0x217
fmt.(*pp).doPrintln(0xc42001e0c0, 0xc420045f28, 0x1, 0x1)
    /usr/local/Cellar/go/1.8.1/libexec/src/fmt/print.go:1138 +0xa1
fmt.Fprintln(0x1108140, 0xc42000c018, 0xc420045f28, 0x1, 0x1, 0xc420045ef0, 0xc420045ee0, 0x1087218)
    /usr/local/Cellar/go/1.8.1/libexec/src/fmt/print.go:247 +0x5c
fmt.Println(0xc420045f28, 0x1, 0x1, 0x10b1e6f, 0x6, 0x0)
    /usr/local/Cellar/go/1.8.1/libexec/src/fmt/print.go:257 +0x57
main.main()
    /tmp/golang-w-python/try_asynchronous.go:21 +0x132
exit status 2

基于需要一次运行多个查询并尝试通过名称跟踪结果，我希望在异步期间写入 map 。但是 fatal error: concurrent map writes 说你不能。

我不明白

1. 为什么不
2. 我应该做什么来同时运行这些大查询。

编辑:

我所拥有的返回结果的最接近的东西不是异步的:

package main

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

var mutex sync.Mutex
var wg sync.WaitGroup

func random_sleep() {
    r := rand.Intn(3000)
    time.Sleep(time.Duration(r) * time.Millisecond)
}

func add_to_map(m map[string] string, word string) {
    defer wg.Done()
    added_word := word + " plus more letters"
    mutex.Lock()
    defer mutex.Unlock()
    fmt.Println("Before sleep")
    random_sleep()
    m[word] = added_word
    fmt.Println("Added word %v", word)
}


func main() {
    words_map := make(map[string]string)
    words := []string{"giraffe", "cat", "dog", "turtle"}
    for _, this_word := range words {
        wg.Add(1)
        go add_to_map(words_map, this_word)
    }
    wg.Wait()
    fmt.Println(words_map)
}

结果错误:

cchilders:~/work_projects/metricsportal/golang_integration (feature/golang-query) 
$ go run try_async.go 
Before sleep
Added word %v turtle
Before sleep
Added word %v cat
Before sleep
Added word %v giraffe
Before sleep
Added word %v dog
map[dog:dog plus more letters turtle:turtle plus more letters cat:cat plus more letters giraffe:giraffe plus more letters]

cchilders:~/work_projects/metricsportal/golang_integration (feature/golang-query) 
$ go run try_async.go 
Before sleep
Added word %v turtle
Before sleep
Added word %v cat
Before sleep
Added word %v giraffe
Before sleep
Added word %v dog
map[dog:dog plus more letters turtle:turtle plus more letters cat:cat plus more letters giraffe:giraffe plus more letters]

结果应该非常快，不超过 3 秒(我认为随机的最大值):

Expectation - 

Before sleep
Before sleep
Before sleep
Before sleep
Added word %v cat
Added word %v giraffe
Added word %v turtle
Added word %v dog

Answer 1

好吧，让我澄清一些事情并帮助你。

你不需要从这里返回修改后的 map ，因为你的函数获取对映射的引用而不是它的副本。 (让我们忽略这个事实你完全忽略了返回值)

func add_to_map(m map[string] string, word string) map[string]string {
    added_word := word + " plus more letters"
    m[word] = added_word
    return m
}

接下来您需要同步对 map 的访问。您可以使用 mutex为此。

import "sync"

var mutex sync.Mutex //glabal variable but can be created as local also

func add_to_map(m map[string] string, word string) {
    added_word := word + " plus more letters"
    // here you can do long to compute task and calculate result
    // calc here
    mutex.Lock() //result ready lock mutex
    defer mutex.Unlock() // unlock mutex when we return from function
    m[word] = added_word // result write to shared map
}

请注意，在 Go 1.9 中会有一个 Concurrent Map类型。

编辑:您需要等待所有 go-routines 完成，因为您的 main() 现在先于它们完成。您可以使用 WaitGroup 来完成此操作

package main

import (
    "fmt"
    "sync"
)

var mutex sync.Mutex
var wg sync.WaitGroup

func add_to_map(m map[string] string, word string) {
    defer wg.Done()
    added_word := word + " plus more letters"
    // do heavy work here
    //
    mutex.Lock()
    defer mutex.Unlock()
    m[word] = added_word
}


func main() {
    words_map := make(map[string]string)
    words := []string{"giraffe", "cat", "dog", "turtle"}
    for _, this_word := range words {
        wg.Add(1)
        go add_to_map(words_map, this_word)
    }
    wg.Wait()
    fmt.Println(words_map)
}