Using DLV to analyze the high CPU consumption of golang process

c++ adopt dbg Analyze memory and cpu, Maybe everyone will . This article mainly analyzes through delve analysis golang Program cpu High occupancy .
delve yes golang Recommended specialty go Language debugging tools , To replace gdb.golang Organizational theory delve Can better understand go Language .
First use vscode Write a simple demo,main.go The code is as follows ：

package main

import (
	"fmt"
	"os"
	"os/signal"
)

func main() {
	fmt.Println("main start")

	msgList := make(chan int, 100)
	go func() {
		for {
			select {
			case <-msgList:
			default:

			}
		}
	}()
	
	c := make(chan os.Signal, 1)
	signal.Notify(c, os.Interrupt, os.Kill)
	s := <-c
	
	fmt.Println("main exit.get signal:", s)
}

go build -o cpudetect main.go Compile the generated cpudetect And put it on the server to run .
Next is the specific analysis steps ：

One 、top Command to see which process ：

top

Tasks: 168 total,   1 running, 166 sleeping,   1 stopped,   0 zombie
%Cpu(s): 94.4 us,  5.6 sy,  0.0 ni,  0.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem :   995684 total,    73064 free,   613904 used,   308716 buff/cache
KiB Swap:  2097148 total,  2093300 free,     3848 used.   200060 avail Mem 

   PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND                                                                                                                   
  7819 root      20   0  703020   1000    632 S 94.1  0.1   3:07.05 cpudetect                                                                                                                 
     1 root      20   0  128296   6704   3912 S  0.0  0.7   0:04.22 systemd                                                                                                                   
     2 root      20   0       0      0      0 S  0.0  0.0   0:00.01 kthreadd                                                                                                                  
     4 root       0 -20       0      0      0 S  0.0  0.0   0:00.00 kworker/0:0H 

You can see cpudetect Process cpu Occupied 94.1.

Two 、top -H -p 7819 Command to view the process cpudetect Specific thread information ：

./dlv attach 7819

top - 01:36:29 up  3:18,  2 users,  load average: 0.68, 0.18, 0.18
Threads:   5 total,   1 running,   4 sleeping,   0 stopped,   0 zombie
%Cpu(s):100.0 us,  0.0 sy,  0.0 ni,  0.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem :   995684 total,    73188 free,   613780 used,   308716 buff/cache
KiB Swap:  2097148 total,  2093300 free,     3848 used.   200184 avail Mem 

   PID USER      PR  NI    VIRT    RES    SHR S %CPU %MEM     TIME+ COMMAND                                                                                                                   
  7823 root      20   0  703020   1000    632 R 99.3  0.1   0:50.62 cpudetect                                                                                                                 
  7819 root      20   0  703020   1000    632 S  0.0  0.1   0:00.00 cpudetect                                                                                                                 
  7820 root      20   0  703020   1000    632 S  0.0  0.1   0:00.06 cpudetect                                                                                                                 
  7821 root      20   0  703020   1000    632 S  0.0  0.1   0:00.01 cpudetect                                                                                                                 
  7822 root      20   0  703020   1000    632 S  0.0  0.1   0:00.00 cpudetect

You can see that the main reason is threads 7823 Occupy cpu Too high .

3、 ... and 、 adopt ./dlv attach 7819 Command start debugging ：

./dlv attach 7819

# Use goroutines Command to view all collaboration information ：
(dlv) goroutines
Goroutine 1 - User: E:/golang/cpuDetect/src/cpudetect/main.go:26 main.main (0x494212)
Goroutine 2 - User: c:/go/src/runtime/proc.go:305 runtime.gopark (0x431ae0)
Goroutine 3 - User: c:/go/src/runtime/proc.go:305 runtime.gopark (0x431ae0)
Goroutine 4 - User: c:/go/src/runtime/proc.go:305 runtime.gopark (0x431ae0)
Goroutine 5 - User: c:/go/src/runtime/proc.go:305 runtime.gopark (0x431ae0)
Goroutine 6 - User: E:/golang/cpuDetect/src/cpudetect/main.go:16 main.main.func1 (0x4942e4) (thread 7823)
Goroutine 7 - User: c:/go/src/runtime/sigqueue.go:147 os/signal.signal_recv (0x44559c)
Goroutine 8 - User: c:/go/src/runtime/proc.go:305 runtime.gopark (0x431ae0)

You can see the synergy 6 Hang on 7823 Under the thread of （7823 Just now cpu High thread occupancy ）.

 # Switch to coroutine 6 And check the specific stack information ：
 (dlv) goroutine 6
 Switched from 6 to 6 (thread 7823)
 (dlv) bt
 0  0x0000000000405a89 in runtime.chanrecv
   at c:/go/src/runtime/chan.go:451
 1  0x0000000000405dca in runtime.selectnbrecv
   at c:/go/src/runtime/chan.go:646
 2  0x00000000004942e4 in main.main.func1
   at E:/golang/cpuDetect/src/cpudetect/main.go:16
 3  0x000000000045dad1 in runtime.goexit
   at c:/go/src/runtime/asm_amd64.s:1373

From the stack information above , You can go to main.go 16 That's ok , Then analyze the corresponding code , You can be sure it's select Medium plus defualt But no treatment led to cpu Idle , Which leads to cpu Too high .
in addition ,dlv There are many other commands for debugging , Let's pass it by ourselves help Command to check .