The Go runtime has several threads, for GC, scheduler, etc.
> On Jun 26, 2019, at 4:48 AM, Subramanian Sridharan <clawsonfir...@gmail.com>
> wrote:
>
> 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?
>
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