CODEWITHSUNDEEP
go
Aravind Yarram
Aravind Yarram

Reputation: 80194

What is the default goroutine?

The following code prints 2009/11/10 23:00:00 Num of goroutines: 1. Is there a way to know which go routine it is?

package main

import (
    "log"
    "runtime"
)

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

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

Upvotes: 1

Views: 212

Answers (1)

Stefano Sanfilippo
Stefano Sanfilippo

Reputation: 33096

It's the main goroutine, encapsulating the main thread of execution. You might for instance observe that by printing goroutine stack traces in your example program:

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)
}

Which produces the following:

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

Notice that runtime.main at the bottom of the trace.

A program with two goroutines alive when the traces are dumped:

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)
}

Will produce something along the lines of:

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

Upvotes: 2

Related Questions