写删读nil map

func main() {
    pvcPods := map[string]map[string]string{}
    if pvcPods["1"] == nil {
        pvcPods["1"] = make(map[string]string)
    }
    pvcPods["1"]["2"] = "1"
    pvcPodNil := map[string]string{}
    p1, ok := pvcPodNil["1"]
    fmt.Printf("p1=%v, ok=%v\n", p1, ok)
    delete(pvcPodNil, "1")
}

运行程序后不会报panic。输出：

p1=, ok=false

定义的pvcPods，一个key为string，value也为map的map类型，先对外层map进行了分配内存；判断如果相应的key对应的value为nil map时，在给内层map分配内存；

定义的pvcPodNil没有初始化，为nil map，直接delete nil map是不会报panic的。

实际上在delete源码可以看到：

// delete内置函数从地图中删除具有指定键（m [key]）的元素。如果m为nil或没有此类元素，则delete为无操作。

map几种定义方式的不同

package main
import "fmt"
type tmap map[string]int
func main() {
    aa := tmap{}
    aa["2"] = 2
    va, ok := aa["2"]
    fmt.Printf("va=%v, ok=%v\n", va, ok)
    bb := map[string]int{}
    bb["2"] = 2
    va, ok = bb["2"]
    fmt.Printf("va=%v, ok=%v\n", va, ok)
    var cc map[string]int
    cc["2"] = 2
    va, ok = cc["2"]
    fmt.Printf("va=%v, ok=%v\n", va, ok)
}

输出：

va=2, ok=true
va=2, ok=true
panic: assignment to entry in nil map
goroutine 1 [running]:
main.main()
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:19 +0x370

前两种都是初始化的map，最后一种用var定义的是没有初始化的map。

并发写map

package main
import (
    "strconv"
)
func main() {
    m1 := make(map[string]string)
    for i := 0; i < 30; i++ {
        go func(in int) {
            s := strconv.Itoa(in)
            m1[s] = s
        }(i)
    }
}

会报错：concurrent map writes

fatal error: concurrent map writes
goroutine 6 [running]:
runtime.throw(0x47c65c, 0x15)
        D:/Program Files/Go/go135/src/runtime/panic.go:774 +0x79 fp=0xc000049f20 sp=0xc000049ef0 pc=0x428859
runtime.mapassign_faststr(0x469380, 0xc000058000, 0x47e499, 0x1, 0x0)
        D:/Program Files/Go/go135/src/runtime/map_faststr.go:211 +0x41e fp=0xc000049f88 sp=0xc000049f20 pc=0x40e8ee
main.main.func1(0xc000058000, 0x1)
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:13 +0x6d fp=0xc000049fd0 sp=0xc000049f88 pc=0x4591dd
runtime.goexit()
        D:/Program Files/Go/go135/src/runtime/asm_amd64.s:1357 +0x1 fp=0xc000049fd8 sp=0xc000049fd0 pc=0x44da51
created by main.main
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11 +0x5d
goroutine 1 [runnable]:
runtime.gopark(0x0, 0x0, 0xc000011008, 0x1)
        D:/Program Files/Go/go135/src/runtime/proc.go:287 +0x145
runtime.main()
        D:/Program Files/Go/go135/src/runtime/proc.go:222 +0x2b4
runtime.goexit()
        D:/Program Files/Go/go135/src/runtime/asm_amd64.s:1357 +0x1
goroutine 29 [runnable]:
main.main.func1(0xc000058000, 0x17)
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11
created by main.main
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11 +0x5d
goroutine 30 [runnable]:
main.main.func1(0xc000058000, 0x18)
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11
created by main.main
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11 +0x5d
goroutine 31 [runnable]:
main.main.func1(0xc000058000, 0x19)
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11
created by main.main
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11 +0x5d
goroutine 32 [runnable]:
main.main.func1(0xc000058000, 0x1a)
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11
created by main.main
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11 +0x5d
goroutine 33 [runnable]:
main.main.func1(0xc000058000, 0x1b)
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11
created by main.main
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11 +0x5d
goroutine 34 [runnable]:
main.main.func1(0xc000058000, 0x1c)
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11
created by main.main
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11 +0x5d
goroutine 35 [runnable]:
main.main.func1(0xc000058000, 0x1d)
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11
created by main.main
        D:/SoftwareAndProgram/program/Go/Development/src/gotools/gotest/main.go:11 +0x5d

并发读map

package main
import (
    "fmt"
    "time"
)
func main() {
    m1 := make(map[string]string)
    m1["1"] = "1"
    for i := 0; i < 100; i++ {
        go func(in int) {
            fmt.Printf("m[1]=%v\n", m1["1"])
        }(i)
    }
    time.Sleep(2*time.Second)
}

运行程序并不会报异常。

修改遍历中的map

package main
import (
    "fmt"
)
func main() {
    m1 := make(map[string]string)
    m1["1"] = "1"
    m1["2"] = "2"
    m1["3"] = "3"
    m1["4"] = "4"
    m1["5"] = "5"
    m1["6"] = "6"
    m1["7"] = "7"
    m1["8"] = "8"
    m1["9"] = "9"
    m1["10"] = "10"
    i := 0
    for k, v := range m1 {
        i++
        if i == 6 {
            m1["11"] = "11"
        }
        fmt.Printf("%v=%v\n", k, v)
    }
}

当i==6时，输出了11

1=1
3=3
4=4
7=7
9=9
2=2
5=5
6=6
8=8
10=10
11=11

当i==8时，没输出11

package main
import (
    "fmt"
)
func main() {
    m1 := make(map[string]string)
    m1["1"] = "1"
    m1["2"] = "2"
    m1["3"] = "3"
    m1["4"] = "4"
    m1["5"] = "5"
    m1["6"] = "6"
    m1["7"] = "7"
    m1["8"] = "8"
    m1["9"] = "9"
    m1["10"] = "10"
    i := 0
    for k, v := range m1 {
        i++
        if i == 8 {
            m1["11"] = "11"
        }
        fmt.Printf("%v=%v\n", k, v)
    }
}

程序输出，没有输出11

3=3
4=4
8=8
10=10
1=1
2=2
5=5
6=6
7=7
9=9

golang学习

删除nil map，写nil map，读nil map，并发写map，修改遍历中的map