Go程序中的三个背景程序是什么？ [英] What are the three background goroutines in a Go program?

问题描述

Go似乎总是有至少4个goroutines在任何时候运行。另外三个不是主要的门厅？

http://play.golang.org/p/MQBiLmHXBK

 包主
 
 import（
fmt
runtime
）
 
 func main（）{
 fmt.Println（runtime.NumGoroutine ））// 4 
} 
  

解决方案

那些不是线程，它们是goroutines，并且数量可能会根据当前的实现而有所不同（例如，在go1.2中它会打印2）。

现在，它看起来像 main 和1 for runtime / gc。

  
 
 
 func main（）{
 fmt.Println（func（）string {panic（nil）; return}（））
} 
  

这显示

  goroutine 16 [running]：
 runtime.panic（0x0，0x0）
 /usr/local/go/src/pkg/runtime/panic.c:279 + 0xf5 
 main.func·001（0x3ea4f，0xdc4b0）
 /test/threads.go:6+ 0x28 
 main.main（）
 /test/threads.go:6+ 0x1e 
 
 goroutine 17 [runnable]：
 runtime.MHeap_Scavenger（）
 /usr/local/go/src/pkg/runtime/mheap.c:507 
 runtime .goexit（）
 /usr/local/go/src/pkg/runtime/proc.c:1445 
 
 goroutine 18 [runnable]：
 bgsweep（）
 /usr/local/go/src/pkg/runtime/mgc0.c:1976 
 runtime.goexit（）
 /usr/local/go/src/pkg/runtime/proc.c:1445 
 
 goroutine 19 [runnable]：
 runfinq（）
 /usr/local/go/src/pkg/runtime/mgc0.c:2606 
 runtime.goexit （）
 /usr/local/go/src/pkg/runtime/proc.c:1445 
  

如果您删除fmt，并使用自引导 print 函数，那么您只能获得2个goroutine。

 $ $ b $ print（runtime.NumGoroutine（），\\\
）
 
 
 //打印2 
  

如果您想要确切知道哪些goroutines正在运行，打印堆栈跟踪，调用panic或使用SIGQUIT（打印堆栈跟踪并退出）终止进程。如果你运行绝对最低限度的程序，你可以看到一个堆栈跟踪，你可以看到2个例程：

  package main 
 
 func main（）{
 panic（nil）
} 
  

< Goroutines非常便宜，许多事情将会启动并停止更多goroutines，因此试图追踪它们的下限并不是很有用。注意，即使只有2个goroutines（main / runtime.panic和runtime.MHeap_Scavenger），count也已经达到了17个。

  panic：nil 
 
 goroutine 16 [running]：
 runtime.panic（0x0,0x0）
 / usr / local / go / src / pkg / runtime / panic.c：279 + 0xf5 
 main.main（）
 /test/threads.go:4+ 0x28 
 
 goroutine 17 [runnable]：
 runtime。 MHeap_Scavenger（）
 /usr/local/go/src/pkg/runtime/mheap.c:507 
 runtime.goexit（）
 / usr / local / go / src / pkg / runtime /proc.c:1445 
退出状态2 
  

Go seems to always have at least 4 goroutines running at any given time. What are the other three that are not the main goroutine?

http://play.golang.org/p/MQBiLmHXBK

package main

import (
    "fmt"
    "runtime"
)

func main() {
    fmt.Println(runtime.NumGoroutine()) //4
}

解决方案

Those aren't threads, they're goroutines, and the number may vary based on current implementation (i.e. in go1.2 it would have printed 2).

Right now, it looks like you have 1 for main, and 3 for runtime/gc.

import "fmt"

func main() {
    fmt.Println(func() string { panic(nil); return "" }())
}

This shows

goroutine 16 [running]:
runtime.panic(0x0, 0x0)
    /usr/local/go/src/pkg/runtime/panic.c:279 +0xf5
main.func·001(0x3ea4f, 0xdc4b0)
    /test/threads.go:6 +0x28
main.main()
    /test/threads.go:6 +0x1e

goroutine 17 [runnable]:
runtime.MHeap_Scavenger()
    /usr/local/go/src/pkg/runtime/mheap.c:507
runtime.goexit()
    /usr/local/go/src/pkg/runtime/proc.c:1445

goroutine 18 [runnable]:
bgsweep()
    /usr/local/go/src/pkg/runtime/mgc0.c:1976
runtime.goexit()
    /usr/local/go/src/pkg/runtime/proc.c:1445

goroutine 19 [runnable]:
runfinq()
    /usr/local/go/src/pkg/runtime/mgc0.c:2606
runtime.goexit()
    /usr/local/go/src/pkg/runtime/proc.c:1445

if you remove fmt, and use the bootstrapping print function you only get 2 goroutines.

import "runtime"

func main() {
    print(runtime.NumGoroutine(), "\n")
}

// prints 2

If you ever want to know exactly what goroutines are running, print a stack trace, call panic, or kill the process with SIGQUIT (which prints a stack trace and exits). If you run the absolute minimum program you can get a stack trace from you can see the 2 goroutines:

package main

func main() {
    panic(nil)
}

Goroutines are very inexpensive, and many things will start and stop more goroutines, so trying to track their lower bound isn't very useful. Notice how even though there's only 2 goroutines, (main/runtime.panic, and runtime.MHeap_Scavenger), the count is already up to 17.

panic: nil

goroutine 16 [running]:
runtime.panic(0x0, 0x0)
    /usr/local/go/src/pkg/runtime/panic.c:279 +0xf5
main.main()
    /test/threads.go:4 +0x28

goroutine 17 [runnable]:
runtime.MHeap_Scavenger()
    /usr/local/go/src/pkg/runtime/mheap.c:507
runtime.goexit()
    /usr/local/go/src/pkg/runtime/proc.c:1445
exit status 2

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