Go runs multiple threads for a serial process

[Subramanian Sridharan]

Hi guys

Today while analyzing CPU usage of one of our processes written in go, I noticed that there were multiple threads associated with the process which is actually serial. (Doesn't make use of goroutines)

I wanted to know if it was the expected behaviour or some issue in our service.

So I tested the same with this snippet:

func main() {
    for {
    }
}

And to my surprise, even this ever running process had multiple threads associated with it:

➜  go build everRunningProgram.go

➜  ./everRunningProgram &

[1] 13745

➜  top -b -n 1 -H -p 13745       

top - 15:07:38 up  4:03,  1 user,  load average: 0.63, 0.80, 0.72

Threads:   5 total,   1 running,   4 sleeping,   0 stopped,   0 zombie

%Cpu(s):  4.9 us,  1.1 sy,  0.3 ni, 93.2 id,  0.0 wa,  0.0 hi,  0.5 si,  0.0 st

KiB Mem : 16301396 total,  4780820 free,  5033472 used,  6487104 buff/cache

KiB Swap:        0 total,        0 free,        0 used. 10270784 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND

13745 mani-86+  25   5  101856    764    584 R 99.9  0.0   0:10.38 everRunningProg

13746 mani-86+  25   5  101856    764    584 S  0.0  0.0   0:00.00 everRunningProg

13747 mani-86+  25   5  101856    764    584 S  0.0  0.0   0:00.00 everRunningProg

13748 mani-86+  25   5  101856    764    584 S  0.0  0.0   0:00.00 everRunningProg

13749 mani-86+  25   5  101856    764    584 S  0.0  0.0   0:00.00 everRunningProg

I tried the same with other programming languages and they didn't seem to exhibit this behaviour.

Rust:

fn main() {

loop {}

}

➜  rustc everRunningProgram.rs

➜  ./everRunningProgram &

[2] 14265

➜  top -b -n 1 -H -p 14265

top - 15:11:36 up  4:07,  1 user,  load average: 1.59, 1.29, 0.95

Threads:   1 total,   1 running,   0 sleeping,   0 stopped,   0 zombie

%Cpu(s):  4.9 us,  1.1 sy,  0.5 ni, 93.0 id,  0.0 wa,  0.0 hi,  0.5 si,  0.0 st

KiB Mem : 16301396 total,  4584980 free,  5132508 used,  6583908 buff/cache

KiB Swap:        0 total,        0 free,        0 used. 10111372 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND

14265 mani-86+  25   5   13156    980    868 R 99.9  0.0   0:10.22 everRunningProg

C:

int main() {

while(1);

}

➜  cc everRunningProgram.c 

➜  ./a.out &             

[3] 14413

➜  top -b -n 1 -H -p 14413

top - 15:14:34 up  4:10,  1 user,  load average: 2.43, 1.81, 1.22

Threads:   1 total,   1 running,   0 sleeping,   0 stopped,   0 zombie

%Cpu(s):  4.8 us,  1.1 sy,  0.8 ni, 92.7 id,  0.0 wa,  0.0 hi,  0.5 si,  0.0 st

KiB Mem : 16301396 total,  4603696 free,  5098020 used,  6599680 buff/cache

KiB Swap:        0 total,        0 free,        0 used. 10134048 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND

14413 mani-86+  25   5    4380    712    648 R 99.9  0.0   0:06.07 a.out

Python:

while True:
    pass

➜  scripts python3 everRunningProgram.py &

[4] 14587

➜  scripts top -b -n 1 -H -p 14587        

top - 15:16:35 up  4:12,  1 user,  load average: 4.08, 2.62, 1.59

Threads:   1 total,   1 running,   0 sleeping,   0 stopped,   0 zombie

%Cpu(s):  4.8 us,  1.1 sy,  1.1 ni, 92.5 id,  0.0 wa,  0.0 hi,  0.5 si,  0.0 st

KiB Mem : 16301396 total,  4551664 free,  5146576 used,  6603156 buff/cache

KiB Swap:        0 total,        0 free,        0 used. 10082516 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND

14587 mani-86+  25   5   33056   8736   5472 R 99.9  0.1   0:06.63 python3

Is there any explanation for this behaviour on Go?
What's really happening behind the scenes?

[Robert Engels]

The Go runtime has several threads, for GC, scheduler, etc. 

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