goroutine leaks

README.md

goroutine がリークする

goroutineは終了しているものの、goroutineがGCされていないようです。

即座にgoroutineが終了(つまり同時に存在するgoroutineの数が多くない)する場合は、ちゃんとGCするみたい。 大量のgoroutineが同時に存在するとGCできずにリークするみたい。

complile.md

ヒープとスタック

routine3

スタックにallocateされている スタックにallocateされたものは、goroutineがGCされていないため余分にリークしている。(47MB)

$ go build -gcflags -m main.go 
# command-line-arguments
./main.go:56: can inline subroutine4
./main.go:46: wghoge escapes to heap
./main.go:44: routine3 make([]byte, 1000) does not escape // <-ここ
./main.go:20: func literal escapes to heap
./main.go:20: func literal escapes to heap
./main.go:23: "start" escapes to heap
./main.go:25: wghoge escapes to heap
./main.go:28: "num goroutine: " escapes to heap
./main.go:28: runtime.NumGoroutine() escapes to heap
./main.go:29: wghoge escapes to heap
./main.go:30: "done" escapes to heap
./main.go:31: "num goroutine: " escapes to heap
./main.go:31: runtime.NumGoroutine() escapes to heap
./main.go:21: http.ListenAndServe("localhost:6060", nil) escapes to heap
./main.go:23: test ... argument does not escape
./main.go:28: test ... argument does not escape
./main.go:30: test ... argument does not escape
./main.go:31: test ... argument does not escape
./main.go:21: test.func1 ... argument does not escape
./main.go:35: wghoge escapes to heap
./main.go:40: wghoge escapes to heap
./main.go:56: subroutine4 buf does not escape
./main.go:50: make([]byte, 1000) escapes to heap
./main.go:53: wghoge escapes to heap

routine4

[]byteはヒープにallocateされている。 ヒープは正しくGCされている。(29MB)

$ go build -gcflags -m main.go 
# command-line-arguments
./main.go:56: can inline subroutine4
./main.go:56: subroutine4 buf does not escape
./main.go:50: make([]byte, 1000) escapes to heap // <- ここ
./main.go:53: wghoge escapes to heap
./main.go:20: func literal escapes to heap
./main.go:20: func literal escapes to heap
./main.go:23: "start" escapes to heap
./main.go:25: wghoge escapes to heap
./main.go:28: "num goroutine: " escapes to heap
./main.go:28: runtime.NumGoroutine() escapes to heap
./main.go:29: wghoge escapes to heap
./main.go:30: "done" escapes to heap
./main.go:31: "num goroutine: " escapes to heap
./main.go:31: runtime.NumGoroutine() escapes to heap
./main.go:21: http.ListenAndServe("localhost:6060", nil) escapes to heap
./main.go:23: test ... argument does not escape
./main.go:28: test ... argument does not escape
./main.go:30: test ... argument does not escape
./main.go:31: test ... argument does not escape
./main.go:21: test.func1 ... argument does not escape
./main.go:35: wghoge escapes to heap
./main.go:40: wghoge escapes to heap
./main.go:46: wghoge escapes to heap
./main.go:44: routine3 make([]byte, 1000) does not escape

main.go

package main

import (
	"log"
	"net/http"
	_ "net/http/pprof"
	"runtime"
	"sync"
	"time"
	"runtime/debug"
)

func main() {
	test()
	runtime.GC()
	debug.FreeOSMemory()
	time.Sleep(3600 * time.Second)
}

var wghoge sync.WaitGroup

func test() {
	go func() {
		log.Println(http.ListenAndServe("localhost:6060", nil))
	}()
	log.Println("start")
	for i := 0; i < 10000; i++ {
		wghoge.Add(1)
		go routine3()
	}
	log.Println("num goroutine: ", runtime.NumGoroutine())
	wghoge.Wait()
	log.Println("done")
	log.Println("num goroutine: ", runtime.NumGoroutine())
}

func routine1() {
	wghoge.Done()
}

func routine2() {
	time.Sleep(time.Second)
	wghoge.Done()
}

func routine3() {
	_ = make([]byte, 10000)
	time.Sleep(time.Second)
	wghoge.Done()
}

func routine4() {
	hello := make([]byte, 1000)
	go subroutine4(hello)
	time.Sleep(time.Second)
	wghoge.Done()
}

func subroutine4(buf []byte) {
	buf[0] = 1
}

result.md

結果

routine1

$ go run main.go 
2017/08/23 18:08:29 start
2017/08/23 18:08:29 num goroutine:  21
2017/08/23 18:08:29 done
2017/08/23 18:08:29 num goroutine:  4

routine2

$ go run main.go 
2017/08/23 18:09:32 start
2017/08/23 18:09:32 num goroutine:  10003
2017/08/23 18:09:33 done
2017/08/23 18:09:33 num goroutine:  3

routine3

$ go run main.go 
2017/08/23 18:10:32 start
2017/08/23 18:10:32 num goroutine:  10003
2017/08/23 18:10:33 done
2017/08/23 18:10:33 num goroutine:  3

routine4

$ go run main.go 
2017/08/23 18:27:53 start
2017/08/23 18:27:53 num goroutine:  10004
2017/08/23 18:27:54 done
2017/08/23 18:27:54 num goroutine:  3