goroutine的栈在其生命周期开始时很小,可能只有2KB,但是它并不固定,可按需增大或减小。虽然我们可以无脑创建很多goroutine来执行操作,但是如果程序出现意外,goroutine可能会暴涨占据内存,一切就变得不可控,比如我们通过循环来创建goroutine,当循环条件满足,创建巨额的goroutine,严重时系统会崩溃。博主也是通过杨旭老师的TCP端口扫描器中发现了这个问题。

1.循环扫描

不使用goroutine,直接循环扫描端口。

package main

import (
	"fmt"
	"net"
	"time"
)

func main() {
	fmt.Println("TCP端口扫描启动...")
	start := time.Now()
	for i := 1; i <= 20; i++ {
		address := fmt.Sprintf("192.168.0.109:%d", i)
		conn, err := net.Dial("tcp", address)
		if err != nil {
			fmt.Printf(" %s 关闭\n", address)
			continue
		}
		conn.Close()
		fmt.Printf(" %s 打开\n", address)
	}

	elasped := time.Since(start) / 1e9
	fmt.Printf("\n 经过了%d秒 \n", elasped)
}

TCP端口扫描启动...
 192.168.0.109:1 关闭
 192.168.0.109:2 关闭
 192.168.0.109:3 关闭
 192.168.0.109:4 关闭
 192.168.0.109:5 关闭
 192.168.0.109:6 关闭
 192.168.0.109:7 关闭
 192.168.0.109:8 关闭
 192.168.0.109:9 关闭
 192.168.0.109:10 关闭
 192.168.0.109:11 关闭
 192.168.0.109:12 关闭
 192.168.0.109:13 关闭
 192.168.0.109:14 关闭
 192.168.0.109:15 关闭
 192.168.0.109:16 关闭
 192.168.0.109:17 关闭
 192.168.0.109:18 关闭
 192.168.0.109:19 关闭
 192.168.0.109:20 关闭

 经过了40秒

2.并发扫描

利用goroutine并发扫描

package main

import (
	"fmt"
	"net"
	"sync"
	"time"
)

var wg sync.WaitGroup

func main() {
	fmt.Println("TCP端口扫描启动...")
	start := time.Now()
	for i := 1; i <= 20; i++ {
		wg.Add(1)
		go func(i int) {
			defer wg.Done()
			address := fmt.Sprintf("192.168.0.109:%d", i)
			conn, err := net.Dial("tcp", address)
			if err != nil {
				fmt.Printf(" %s 关闭\n", address)
				return
			}
			conn.Close()
			fmt.Printf(" %s 打开\n", address)
		}(i)
	}
	wg.Wait()
	elasped := time.Since(start) / 1e9
	fmt.Printf("经过了%d秒", elasped)
}

TCP端口扫描启动...
 192.168.0.109:4 关闭
 192.168.0.109:6 关闭 
 192.168.0.109:11 关闭
 192.168.0.109:7 关闭 
 192.168.0.109:8 关闭 
 192.168.0.109:14 关闭
 192.168.0.109:3 关闭
 192.168.0.109:20 关闭
 192.168.0.109:16 关闭
 192.168.0.109:12 关闭
 192.168.0.109:1 关闭
 192.168.0.109:17 关闭
 192.168.0.109:18 关闭
 192.168.0.109:13 关闭
 192.168.0.109:9 关闭
 192.168.0.109:10 关闭
 192.168.0.109:5 关闭
 192.168.0.109:15 关闭
 192.168.0.109:19 关闭
 192.168.0.109:2 关闭
经过了2秒

即使代码改成全端口1~65535,时间也只有21s

package main

import (
	"fmt"
	"net"
	"sync"
	"time"
)

var wg sync.WaitGroup

func main() {
	fmt.Println("TCP端口扫描启动...")
	start := time.Now()
	for i := 1; i <= 65535; i++ {
		wg.Add(1)
		go func(i int) {
			defer wg.Done()
			address := fmt.Sprintf("192.168.0.109:%d", i)
			conn, err := net.Dial("tcp", address)
			if err != nil {
				fmt.Printf(" %s 关闭\n", address)
				return
			}
			conn.Close()
			fmt.Printf(" %s 打开\n", address)
		}(i)
	}
	wg.Wait()
	elasped := time.Since(start) / 1e9
	fmt.Printf("\n 经过了%d秒 \n", elasped)
}

 ...
 192.168.0.109:39702 关闭
 192.168.0.109:37282 关闭
 192.168.0.109:39490 关闭
 192.168.0.109:39795 关闭
 192.168.0.109:39613 关闭
 192.168.0.109:39707 关闭
 192.168.0.109:39723 关闭
 192.168.0.109:39732 关闭
 192.168.0.109:39806 关闭
 192.168.0.109:39682 关闭
 192.168.0.109:39809 关闭
 192.168.0.109:39663 关闭
 192.168.0.109:40006 关闭
 192.168.0.109:39712 关闭
 192.168.0.109:39804 关闭
 192.168.0.109:39731 关闭
 192.168.0.109:39701 关闭
 192.168.0.109:39810 关闭
 192.168.0.109:39725 关闭
 192.168.0.109:39805 关闭
 192.168.0.109:39713 关闭
 192.168.0.109:39489 关闭
 192.168.0.109:39791 关闭
 192.168.0.109:39640 关闭
 192.168.0.109:39667 关闭
 192.168.0.109:39661 关闭

 经过了21秒

这里也可以看出使用goroutine做并发操作,真的很快。

3.goroutine pool(池)

上一节最后这样做,就创建了6w多次goroutine,如果数值更大,100w1个亿(当然IP端口数字没这么大),只是做大胆试验:然后就可以在监控内存的悬浮窗看到内存噌噌噌的往上涨,内存迅速消耗殆尽,直至系统卡死,甚至蓝屏。

为了避免这种情况,我们急需创建类似于线程池的机制,去限定我们创建goroutine的数量,并复用。创建固定数量的mgoroutine,利用channel的机制,往channel中传递n个数据,然后分配给这mgoroutine,m<=n。

同样是端口扫描任务,代码改造如下:

package main

import (
	"fmt"
	"net"
)

func main() {
	fmt.Println("TCP端口扫描启动...")
	fmt.Println("下列端口状态为打开:")
	n := make(chan int, 100)
	results := make(chan int, 100)
    
    //创建20000个goroutine
	for m := 0; m < 20000; m++ {
		go worker(n, results)
	}
    
    //channel代表了任务数量
	for i := 1; i < 65535; i++ {
		n <- i
	}
    close(n)
    
    //结果
	for port := range results {
		fmt.Println(port)
	}

}

func worker(ports <-chan int, results chan<- int) {
	for port := range ports {
		address := fmt.Sprintf("192.168.0.109:%d", port)
		conn, err := net.Dial("tcp", address)
		if err != nil {
			// fmt.Printf(" %s 关闭\n", address)
			continue
		}
		conn.Close()
		// fmt.Printf(" %s 打开\n", address)
		results <- port
	}
}

TCP端口扫描启动...
下列端口状态为打开:
80
81   
139  
902  
443  
445  
135  
912  
1433 
2383 
2179 
3306 
5357 
5040 
7680 
8080 
33060
43094
43095
49672
49664
49667
49666
49670
49665
50272