pprof in golang: Fix a memory leak

With rare exceptions ( one , two << the original is formatted worse, IMO ) articles about "profiling" in golang are a reprint of the annotation to the pprof package (not even this old article ) and then a little personal experience about how (not) succeeded with the help pprof find the problem.

Nuance

, google "" "" . "" "" "golang pprof" - . , .

, "" . - / , , () . " ", .

: "" - "". ( , .) ( ) " ", ( " ") 20+.

" " - " ". ( ) . , "", "". , " " . "". " " .

• . , , ( ) "" go. - , goroutines …

  
  
  
  
  

, - ́ "pprof.WriteHeapProfile()". : " " "" 512. ( "").

"́ ": "WriteTo()" "" "debug=2":

pprof.Lookup("heap").WriteTo(some_file, 2)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

pprof, . , " " .

• , "net/http/pprof" curl/wget. , : "http.ListenAndServe()" , . .. "ListenAndServe()" . "go …" goroutine.

  
  
  
  
  

pprof ( ). .

1. HeapProfile

import (
	"runtime"
	"runtime/pprof"
)
…
// Debug: pprof.WriteHeapProfile()
				memprofile := "/run/dnsd/memprofile"
				f, _ := os.Create(memprofile)
				runtime.GC() // get up-to-date statistics
				pprof.WriteHeapProfile(f)
				f.Close()
…
// Debug: pprof http listener
//	go http.ListenAndServe("localhost:8080", nil)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

• , . — curl.

  
  
  
  
  

2.

( 512 4…6 ), 99% .

goroutine "main.apiCall.func1()" 10923 "". (, .. "" 512 . - …)

# go tool pprof -nodefraction=0 -inuse_objects memprofile.3+
File: dnsd
Type: inuse_objects
Time: Dec 24, 2020 at 10:38am (MSK)
Entering interactive mode (type "help" for commands, "o" for options)
(pprof) top
Showing nodes accounting for 19387, 100% of 19387 total
Showing top 10 nodes out of 32
      flat  flat%   sum%        cum   cum%
     10923 56.34% 56.34%      10923 56.34%  main.apiCall.func1
      8192 42.26% 98.60%       8192 42.26%  regexp.mergeRuneSets.func2
       256  1.32% 99.92%        256  1.32%  bufio.NewWriterSize
        16 0.083%   100%         16 0.083%  compress/flate.(*dictDecoder).init
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

3. /

:

	// To complete report processing even after return on timeout
	go func () {
		defer report.DelNotifier(commands.UUID)

		signals := make(chan os.Signal, 1)
		signal.Notify(signals, syscall.SIGHUP, syscall.SIGINT, syscall.SIGKILL, syscall.SIGTERM)
		for {
			select {
			case index := <-callback:
				if (index + 1) >= len(Workers) {
					done <- struct{}{}
					return
				}
			case t:= <- timer: // t++ on each tick, t=-1 at the end
				if t > 0 {
					xl.Warn("apiCall: Timer tick while still not enough reports from workers!")
				}
				if t < 0 { // Time is over
					xl.Err("apiCall: Time over while still not enough reports from workers!")
					err = fmt.Errorf("Time over")
					done <- struct{}{}
					return
				}
			case exitSignal = <-signals:
				xl.Warnf("apiCall: Interrupt is detected: %s", exitSignal)
				xl.Warn("apiCall: Waiting for timeout to complete report processing...")
				err = fmt.Errorf("Interrupt")
				done <- struct{}{}
				return
			}
		}
	} ()
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

4.

, "" "commands.UUID" (commands "" ). , .. "" defer. , . - . - :

go func (uuid string) {
…
} (commands.UUID)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

SIGKILL (""), . , - - .

, "". - ? :

		signal.Notify(signals, syscall.SIGHUP, syscall.SIGINT, syscall.SIGKILL, syscall.SIGTERM)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, "defer report.DelNotifier()" . "signal.Notify()" , . , "os.Signal" " " . . , , " ".

, , " ". "" , "" — .

5. Happy end

:

defer signal.Stop(signals)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, :

# go tool pprof -nodefraction=0 -inuse_objects memprofile.1
File: dnsd
Type: inuse_objects
Time: Dec 25, 2020 at 11:56am (MSK)
No samples were found with the default sample value type.
Try "sample_index" command to analyze different sample values.
Entering interactive mode (type "help" for commands, "o" for options)
(pprof) top
Showing nodes accounting for 0, 0% of 0 total
      flat  flat%   sum%        cum   cum%
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

() . . " " .

.

, "" ( ""). () , .. "" ( "" ).

golang, , " ". ( ) :

• . ( " ") "", . — …

  
  
  
  
  

• "" goroutine ( "" ).

  
  
  
  
  

• "defer …" ( - goroutine, ).

  
  
  
  
  

• "" ( "signal.Notify()") .

  
  
  
  
  

go1.14. 1.8. 1.8 30 . .

I had to refrain from trying go1.15. Because the hipsters who sneaked in broke the X.509 "CommonName" support when checking certificates. (Traditionally) not knowing that apart from the public Internet there are also all sorts of "closed" segments, with high lags for making changes.

So that is all.

Constructive criticism and finger pointing "where am I a fool" is welcome.

Taking this opportunity, everyone with the coming year 2021!