go - 默认的 goroutine 是什么？

Question

以下代码打印 2009/11/10 23:00:00 Num of goroutines: 1。有没有办法知道它是哪个 go 例程？

package main

import (
    "log"
    "runtime"
)

func main() {
    r := runtime.NumGoroutine()
    log.Println("Num of goroutines: ", r)
}

https://play.golang.org/p/pFOG6EQEYb

Answer 1

是主goroutine，封装了执行的主线程。例如，您可能会通过在示例程序中打印 goroutine 堆栈跟踪来观察:

package main

import (
    "log"
    "os"
    "runtime"
    "runtime/pprof"
)

func main() {
    r := runtime.NumGoroutine()
    log.Println("Num of goroutines: ", r)
    pprof.Lookup("goroutine").WriteTo(os.Stdout, 1)
}

产生以下内容:

2009/11/10 23:00:00 Num of goroutines:  1
goroutine profile: total 1
1 @ 0xa22a0 0xa1fc0 0x9d640 0x20180 0x5a0a0 0x98e81
#   0xa229f runtime/pprof.writeRuntimeProfile+0xdf  /usr/local/go/src/runtime/pprof/pprof.go:614
#   0xa1fbf runtime/pprof.writeGoroutine+0x9f   /usr/local/go/src/runtime/pprof/pprof.go:576
#   0x9d63f runtime/pprof.(*Profile).WriteTo+0xff   /usr/local/go/src/runtime/pprof/pprof.go:298
#   0x2017f main.main+0x17f             /tmp/sandbox832735226/main.go:13
#   0x5a09f runtime.main+0x39f          /usr/local/go/src/runtime/proc.go:183

请注意跟踪底部的 runtime.main。

转储痕迹时有两个 goroutine 的程序:

package main

import (
    "log"
    "os"
    "runtime"
    "runtime/pprof"
)

func main() {
    c := make(chan int)
    go func() { <-c }()
    r := runtime.NumGoroutine()
    log.Println("Num of goroutines: ", r)
    pprof.Lookup("goroutine").WriteTo(os.Stdout, 1)
}

将产生以下内容:

2009/11/10 23:00:00 Num of goroutines:  2
goroutine profile: total 2
1 @ 0x20220 0x98f61
#   0x20220 main.main.func1+0x0 /tmp/sandbox584983760/main.go:12

1 @ 0xa2380 0xa20a0 0x9d720 0x201e0 0x5a180 0x98f61
#   0xa237f runtime/pprof.writeRuntimeProfile+0xdf  /usr/local/go/src/runtime/pprof/pprof.go:614
#   0xa209f runtime/pprof.writeGoroutine+0x9f   /usr/local/go/src/runtime/pprof/pprof.go:576
#   0x9d71f runtime/pprof.(*Profile).WriteTo+0xff   /usr/local/go/src/runtime/pprof/pprof.go:298
#   0x201df main.main+0x1df             /tmp/sandbox584983760/main.go:15
#   0x5a17f runtime.main+0x39f          /usr/local/go/src/runtime/proc.go:183