golang写文件时阻塞了很多goroutine，为什么不创建很多线程?

问题描述

正如我们在 go 中所知，当 goroutine 必须执行阻塞调用时，可能会创建一个线程，例如系统调用，或通过 cgo 调用 C 库.一些测试代码:

As we know in go, a thread may be created when the goroutine has to perform a blocking call, such as a system call, or a call to a C library via cgo. Some test code:

   package main

   import (
        "io/ioutil"
        "os"
        "runtime"
        "strconv"
    )

    func main() {
        runtime.GOMAXPROCS(2)
        data, err := ioutil.ReadFile("./55555.log")
        if err != nil {
            println(err)
            return
        }
        for i := 0; i < 200; i++ {
            go func(n int) {
                for {
                    err := ioutil.WriteFile("testxxx"+strconv.Itoa(n), []byte(data), os.ModePerm)
                    if err != nil {
                        println(err)
                        break
                    }
                }
            }(i)
        }
        select {}
    }

当我运行它时，它没有创建很多线程.

When I run it, it didn't create many threads.

➜ =99=[root /root]$ cat /proc/9616/status | grep -i thread
Threads:    5

有什么想法吗?

推荐答案

我稍微修改了你的程序以输出更大的块

I altered your program slightly to output a much bigger block

package main

import (
    "io/ioutil"
    "os"
    "runtime"
    "strconv"
)

func main() {
    runtime.GOMAXPROCS(2)
    data := make([]byte, 128*1024*1024)
    for i := 0; i < 200; i++ {
        go func(n int) {
            for {
                err := ioutil.WriteFile("testxxx"+strconv.Itoa(n), []byte(data), os.ModePerm)
                if err != nil {
                    println(err)
                    break
                }
            }
        }(i)
    }
    select {}
}

这会如您所愿地显示 >200 个线程

This then shows >200 threads as you expected

$ cat /proc/17033/status | grep -i thread
Threads:    203

所以我认为系统调用在您的原始测试中退出得太快，无法显示您期望的效果.

So I think the syscalls were exiting too quickly in your original test to show the effect you were expecting.

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