goroutine

# goroutine

package main

import (
	"fmt"
	"time"
)

func main() {
	for i := 0; i < 1000; i++ {
		go func(i int) {
			for {
                // io 操作 会交出控制权
				fmt.Printf("hello from"+
					"goroutine + %d\n", i)
			}
		}(i)
	}

	time.Sleep(time.Millisecond)
}

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协程：Coroutine，是一个轻量级的”线程“。

非抢占式多任务处理，由协程主动交出控制权
编译器、解释器、虚拟机层面的多任务，具体实现上会由调度器管理
多个协程可能在一个或多个线程上运行

我们如果把这个i不传递参数会怎么样？

func main() {
    var a [10]int
	for i := 0; i < 10; i++ {
		go func() {
			for {
                a[i]++
                // 手动交出控制权
				runtime.Goexit()
			}
		}()
	}

	time.Sleep(time.Millisecond)
}

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这样就会报错，会提示超出边界的panic，这是为什么呢?

因为使用的是同一个i，当main线程执行完之后，i最后的值会变成 10，如果此时a[10]++，就会报超出边界的panic。

我们可以通过命令行参数来进行查看对比：

➜ go run -race goroutine.go
==================
WARNING: DATA RACE
Read at 0x00c0000c4018 by goroutine 7:
  main.main.func1()
      /Users/GolangProjects/src/learngo/goroutine/goroutine.go:14 +0x70

Previous write at 0x00c0000c4018 by main goroutine:
  main.main()
      /Users/GolangProjects/src/learngo/goroutine/goroutine.go:11 +0xc6

Goroutine 7 (running) created at:
  main.main()
      /Users/GolangProjects/src/learngo/goroutine/goroutine.go:12 +0xa4
==================
==================
WARNING: DATA RACE
Read at 0x00c0000c8010 by goroutine 7:
  main.main.func1()
      /Users/GolangProjects/src/learngo/goroutine/goroutine.go:14 +0x94

Previous write at 0x00c0000c8010 by goroutine 8:
  main.main.func1()
      /Users/GolangProjects/src/learngo/goroutine/goroutine.go:14 +0x4b

Goroutine 7 (running) created at:
  main.main()
      /Users/GolangProjects/src/learngo/goroutine/goroutine.go:12 +0xa4

Goroutine 8 (finished) created at:
  main.main()
      /Users/GolangProjects/src/learngo/goroutine/goroutine.go:12 +0xa4
==================
panic: runtime error: index out of range [10] with length 10

goroutine 28 [running]:
main.main.func1()
        /Users/GolangProjects/src/learngo/goroutine/goroutine.go:14 +0xde
created by main.main
        /Users/GolangProjects/src/learngo/goroutine/goroutine.go:12 +0xa5
exit status 2

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我们加上传递参数的之后再次运行：

➜ go run -race goroutine.go
==================
WARNING: DATA RACE
Read at 0x00c0000c8000 by main goroutine:
  runtime.racereadrange()
      <autogenerated>:1 +0x1b

Previous write at 0x00c0000c8000 by goroutine 7:
  main.main.func1()
      /Users/GolangProjects/src/learngo/goroutine/goroutine.go:14 +0x64
  main.main·dwrap·1()
      /Users/GolangProjects/src/learngo/goroutine/goroutine.go:18 +0x47

Goroutine 7 (finished) created at:
  main.main()
      /Users/GolangProjects/src/learngo/goroutine/goroutine.go:12 +0x7d
==================
[1 1 1 1 1 1 1 1 1 1]
Found 1 data race(s)
exit status 66