Golang中 goroutine执行速度的问题

本文关注Golang中for循环开启goroutine的执行顺序问题。实验表明,for循环本身比在循环中启动goroutine快;然而,启动goroutine与第一个fmt.Println的执行速度可能接近。特别是,第二个for循环的fmt比goroutine中的fmt更快,可能是由于channel操作的延迟。最后,main函数结束时,goroutine中的某些任务可能仍未完成。

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突然想到了之前一直没留意的for循环中开goroutine的执行顺序问题,就找了段代码试了试,试了几次后发现几个有意思的地方,我暂时没有精力往更深处挖掘,希望有golang大神能简单说一说这几个地方是怎么回事。

代码: 

package main  
import "fmt"

func Count(ch chan int) {
	fmt.Println("Count doing")
	ch <- 1
	fmt.Println("Counting")
}

func main() {
    chs := make([]chan int, 100)
	for i := 0; i < 100; i++ {
		chs[i] = make(chan int)
		go Count(chs[i])
		fmt.Println("Count",i)
	}
	for i, ch := range chs {
		<-ch
		fmt.Println("Counting ", i)
	}
} 

试了几次之后,反复的想goroutine执行的问题。

根据下面的输出,我能看到的是:
1. for循环的速度 比 for中开出goroutine并执行的速度 执行的快
2. 但是 开goroutine和执行第一个fmt的速度可能赶上 for循环的速度 比如前12个count和count doing
3. 关键问题,第二个for循环执行的fmt竟然要比goroutine中的第二个fmt快??(放入channel很耗时?)
4. main结束时,也就是第二个for循环结束时, 还有goroutine中的第二个fmt没执行 

输出:

Count 0
Count 1
Count 2
Count 3
Count 4
Count 5
Count 6
Count 7
Count 8
Count 9
Count 10
Count 11
Count doing
Count doing
Count doing
Count doing
Count doing
Count 12
Count doing
Count doing
Count doing
Count doing
Count doing
Count doing
Count doing
Count 13
Count 14
Count 15
Count 16
Count 17
Count 18
Count 19
Count 20
Count 21
Count doing
Count doing
Count doing
Count 22
Count doing
Count doing
Count doing
Count 23
Count 24
Count 25
Count 26
Count 27
Count 28
Count 29
Count 30
Count doing
Count 31
Count doing
Count doing
Count 32
Count 33
Count 34
Count 35
Count doing
Count 36
Count doing
Count doing
Count 37
Count 38
Count doing
Count doing
Count doing
Count doing
Count 39
Count 40
Count 41
Count 42
Count 43
Count doing
Count doing
Count 44
Count 45
Count 46
Count 47
Count doing
Count 48
Count 49
Count doing
Count doing
Count 50
Count 51
Count doing
Count doing
Count doing
Count doing
Count doing
Count 52
Count 53
Count doing
Count doing
Count doing
Count doing
Count 54
Count doing
Count 55
Count 56
Count 57
Count 58
Count 59
Count 60
Count 61
Count 62
Count 63
Count 64
Count 65
Count doing
Count doing
Count doing
Count 66
Count 67
Count 68
Count 69
Count doing
Count 70
Count doing
Count 71
Count 72
Count doing
Count 73
Count doing
Count doing
Count 74
Count doing
Count 75
Count 76
Count 77
Count doing
Count doing
Count doing
Count doing
Count 78
Count 79
Count 80
Count 81
Count 82
Count 83
Count 84
Count 85
Count 86
Count 87
Count 88
Count 89
Count 90
Count 91
Count 92
Count 93
Count 94
Count doing
Count doing
Count doing
Count doing
Count doing
Count doing
Count doing
Count doing
Count 95
Count doing
Count 96
Count doing
Count 97
Count 98
Count doing
Count 99
Count doing
Count doing
Counting  0
Counting  1
Counting  2
Counting  3
Counting  4
Counting  5
Counting  6
Count doing
Count doing
Counting  7
Counting  8
Count doing
Counting
Count doing
Counting  9
Counting
Count doing
Count doing
Count doing
Count doing
Count doing
Counting
Count doing
Count doing
Count doing
Counting
Count doing
Counting
Count doing
Counting  10
Counting  11
Counting
Count doing
Count doing
Count doing
Count doing
Count doing
Count doing
Counting
Count doing
Count doing
Counting
Counting
Count doing
Count doing
Count doing
Count doing
Counting
Count doing
Counting
Count doing
Count doing
Counting  12
Counting  13
Counting  14
Counting  15
Counting  16
Counting  17
Counting  18
Counting  19
Counting  20
Counting  21
Counting  22
Counting  23
Counting  24
Counting  25
Counting  26
Counting  27
Counting  28
Counting  29
Counting  30
Counting  31
Counting  32
Counting  33
Counting  34
Counting  35
Counting  36
Counting  37
Counting  38
Counting  39
Counting  40
Counting  41
Counting  42
Counting  43
Counting  44
Counting  45
Counting  46
Counting  47
Counting  48
Counting  49
Counting  50
Counting  51
Counting  52
Counting  53
Counting  54
Counting  55
Counting  56
Counting
Counting
Counting
Counting
Counting
Counting
Count doing
Counting
Count doing
Counting
Counting
Counting  57
Counting  58
Counting  59
Counting  60
Counting  61
Counting  62
Counting  63
Counting  64
Counting  65
Counting  66
Counting  67
Counting  68
Counting  69
Counting  70
Counting  71
Counting  72
Counting  73
Counting  74
Counting  75
Counting  76
Counting
Counting
Counting
Counting
Counting
Counting
Counting
Counting
Counting
Counting
Counting
Counting
Counting
Counting
Counting
Counting
Counting
Counting
Counting
Counting  77
Counting  78
Counting  79
Counting  80
Counting  81
Counting  82
Counting  83
Counting  84
Counting  85
Counting  86
Counting  87
Counting  88
Counting  89
Counting  90
Counting  91
Counting  92
Counting  93
Counting  94
Counting  95
Counting  96
Counting  97
Counting  98
Counting  99

 


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