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cmd/compile: a slice captured by a closure might leak #48254

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hajimehoshi opened this issue Sep 8, 2021 · 2 comments
Closed

cmd/compile: a slice captured by a closure might leak #48254

hajimehoshi opened this issue Sep 8, 2021 · 2 comments

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@hajimehoshi
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@hajimehoshi hajimehoshi commented Sep 8, 2021

What version of Go are you using (go version)?

$ go version
go version go1.17 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/hajimehoshi/Library/Caches/go-build"
GOENV="/Users/hajimehoshi/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/hajimehoshi/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/hajimehoshi/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.17"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/hajimehoshi/test/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/60/khbk2xqn1c5bml1byjn89dwc0000gn/T/go-build3631899530=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Run this and see the memory usage (I saw "Real Private Memory" on Activity on macOS):

package main

import (
        "time"
        "runtime"
)

var f func()

func foo(bs []byte) {
        if f == nil {
                copied := make([]byte, len(bs))
                copy(copied, bs)
                f = func() {
                        foo(copied)
                }
                return
        }

        println(len(bs))
}

func main() {
        bs := make([]byte, 100*1024*1024)
        foo(bs)

        f()
        f = nil
        bs = nil

        for {
                runtime.GC()
                time.Sleep(time.Second)
        }
}

What did you expect to see?

The private memory usage should be the same as this program (less than 10[MB] maybe):

func main() {
        for {
                runtime.GC()
                time.Sleep(time.Second)
        }
}

What did you see instead?

The private memory usage keeps about 200[MB]

@randall77
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@randall77 randall77 commented Sep 8, 2021

Seems ok to me:

% top -ncols 8 | grep issue48254
76731  issue48254       0.0  00:00.19 7      0   16+    208M+ 
76731  issue48254       2.2  00:00.21 8      0   17+    203M- 
76731  issue48254       4.5  00:00.26 8      0   17     192M- 
76731  issue48254       4.5  00:00.30 8      0   17     182M- 
76731  issue48254       4.5  00:00.35 8      0   17     171M- 
76731  issue48254       4.4  00:00.40 8      0   17     160M- 
76731  issue48254       4.4  00:00.44 8/1    0   17     149M- 
76731  issue48254       4.5  00:00.50 8      0   17     138M- 
76731  issue48254       4.4  00:00.54 8      0   17     128M- 
76731  issue48254       4.4  00:00.59 8      0   17     118M- 
76731  issue48254       4.5  00:00.64 8      0   17     107M- 
76731  issue48254       6.3  00:00.70 8      0   17     88M-  
76731  issue48254       5.7  00:00.76 8      0   17     71M-  
76731  issue48254       4.7  00:00.81 8      0   17     60M-  
76731  issue48254       4.7  00:00.86 8      0   17     48M-  
76731  issue48254       4.7  00:00.91 8      0   17     37M-  
76731  issue48254       4.7  00:00.96 8      0   17     26M-  
76731  issue48254       4.7  00:01.02 8      0   17     12M-  
76731  issue48254       1.5  00:01.03 8      0   17     8480K-
76731  issue48254       0.0  00:01.03 8      0   17     8512K+
76731  issue48254       0.1  00:01.03 8      0   17     8416K-
76731  issue48254       0.0  00:01.04 8      0   17     8416K 

I see the same memory reduction pattern when using Activity Monitor.

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@hajimehoshi
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@hajimehoshi hajimehoshi commented Sep 8, 2021

Ah OK, I didn't realized the memory usage is decreased gradually... Thanks!

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@hajimehoshi hajimehoshi closed this Sep 8, 2021
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