Golang 程序问题(协程数量控制)

Question

问题描述

我试着用sync.WaitGroup限制协程数量，来写一个端口扫描器，但当协程数量过多的时候，扫描出的结果达不到预期。

如：

设置1000协程，可以扫出80,443,8000,3389
然而设置2000协程后，只能扫出80,443

问题出现的环境背景及自己尝试过哪些方法

在StackOverflow上问过这个问题，英文的回答不是很明白...

这是原回答

You do not wait for the two "non-worker" goroutines in main, so as soon as wg.Wait() there returns, the process shuts down, tearing down any outstanding goroutines.

Since one of them is processing the results, this appears to you as if not all the tasks were processed (and this is true).

以及另一个回答直接给出了优化后的代码：https://play.golang.org/p/_ZD...，在Windows下可行，Linux下一样不行。

相关代码

package main

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

type Job struct {
    host string
    port int
}

type Result struct {
    job    Job
    status bool
}

var jobs = make(chan Job)
var results = make(chan Result)

func worker(wg *sync.WaitGroup) {
    for job := range jobs {
        _, err := net.DialTimeout("tcp", fmt.Sprintf("%s:%d", job.host, job.port), time.Millisecond*1500)
        if err != nil {
            results <- Result{job, false}
        } else {
            results <- Result{job, true}
        }
    }
    wg.Done()
}

const host = "127.0.0.1"

func main() {
    wg := sync.WaitGroup{}

    go func() {
        for i := 1; i < 65535; i++ {
            jobs <- Job{host, i}
        }
        close(jobs)
    }()

    go func() {
        for result := range results {
            if result.status {
                fmt.Println(result.job, "open")
            }
        }
    }()

    for i := 1; i < 4500; i++ {
        wg.Add(1)
        go worker(&wg)
    }
    wg.Wait()
}

你期待的结果是什么？实际看到的错误信息又是什么？

我希望无论是Win还是Linux都能够获取到所有的端口开放情况。

在Windows中由于扫描速度不快，可以扫描出全部端口

{127.0.0.1 135} open
{127.0.0.1 443} open
{127.0.0.1 445} open
{127.0.0.1 808} open
{127.0.0.1 902} open
{127.0.0.1 912} open

Linux下，就达不到预期了

ubuntu@pc:~/Desktop$ go run port.go 
{127.0.0.1 80} open
{127.0.0.1 631} open
{127.0.0.1 3306} open

Answer 1

你这个问题不是golang代码的问题，应该是Linux默认配置的问题：
net.DialTimeout这个函数最终其实就是调用linux socket，而linux中任何东西都是文件，同时linux默认允许同时打开的文件数是1024，可以用如下命令查看：

[root@aia-db /home/daik/test/src/scanport]# ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 3757
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 3757
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

可以看到open files那一行，默认是1024，所以当你启动远远大于1024个协程时（如你代码中设置的4500），就有可能同时打开超过1024个文件，导致socket链接建立失败，
我测试了下(注：我本地环境你用你的代码每次50051这个端口都打印不出来，所以选择这个端口做测试)：

[root@scanport]# go run main.go
{127.0.0.1 25} open
{127.0.0.1 139} open
{127.0.0.1 111} open
{127.0.0.1 445} open
{127.0.0.1 22} open
{127.0.0.1 631} open
{127.0.0.1 9999} open
{127.0.0.1 9998} open
{127.0.0.1 9997} open
I am port 50051, error: dial tcp 127.0.0.1:50051: socket: too many open files
success is  9
fail is  65526

修改方法：
1、降低协程数量，协程数量真不是越多越高效，要根据实际情况
2、修改linux的配置限制，方法如下：

[root@aia-db /home/daik/test/src/scanport]# ulimit -SHn 10000
[root@aia-db /home/daik/test/src/scanport]# ulimit -n
10000
[root@aia-db /home/daik/test/src/scanport]# ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 3757
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 10000
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 3757
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

然后再测试你的代码应该OK了。

我的测试代码：

package main

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

type Job struct {
    host string
    port int
}

type Result struct {
    job    Job
    status bool
}

var success uint32
var fail uint32
var successMux sync.Mutex
var failMux sync.Mutex

var jobs = make(chan Job)
var results = make(chan Result)

func worker(wg *sync.WaitGroup) {
    for job := range jobs {
        _, err := net.DialTimeout("tcp", fmt.Sprintf("%s:%d", job.host, job.port), time.Millisecond*5500)
        if err != nil {
            failMux.Lock()
            fail++
            failMux.Unlock()
            if job.port == 50051 {
                fmt.Println("I am port 50051, error:", err.Error())
            }
            results <- Result{job, false}
        } else {
            successMux.Lock()
            success++
            successMux.Unlock()
            results <- Result{job, true}
        }
    }
    wg.Done()
}

const host = "127.0.0.1"

func main() {
    wg := sync.WaitGroup{}

    go func() {
        for i := 1; i <= 65535; i++ {
            jobs <- Job{host, i}
        }
        close(jobs)
    }()

    go func() {
        for result := range results {
            if result.status {
                fmt.Println(result.job, "open")
            }
        }
    }()

    for i := 0; i < 4500; i++ {
        wg.Add(1)
        go worker(&wg)
    }
    wg.Wait()

    fmt.Println("success is ", success)
    fmt.Println("fail is ", fail)
}

另外，你文中提到的https://play.golang.org/p/_ZD...，
这个代码跟你的其实没有本质区别，应该也是linux的问题，所以才有在Windows和Linux上执行有不同结果的现象出现。