syscall/js: implement GC of refs

[hajimehoshi]

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

$ go version
go version go1.13.1 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=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
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"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/ht/ky_bwgzs4bd5z1hh02k34x_h0000gn/T/go-build424384589=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Build this program with GOOS=js GOARCH=wasm and see the browser (with wasm_exec.js and so on). I tested this with Chrome Version 77.0.3865.120 (Official Build) (64-bit)

package main

import (
        "syscall/js"
)

var (
        requestAnimationFrame = js.Global().Get("requestAnimationFrame")
)

func main() {
        var cf js.Func
        f := func(this js.Value, args []js.Value) interface{} {
                requestAnimationFrame.Invoke(cf)
                return nil
        }
        cf = js.FuncOf(f)
        f(js.Value{}, nil)
        select {}
}

What did you expect to see?

No memory leak

What did you see instead?

The memory usage keeps increasing in the long run.

The memory usage rises and falls in a cycle fashion, but it seems that the peak memory usage keeps increasing.

crbug.com/120186 might be related.

CC @agnivade

[hajimehoshi]

I could not reproduce this issue on Firefox (69.0.1 (64-bit)) Reproduced also on Firefox

[hajimehoshi]

I inserted a debug printing like this:

@@ -182,6 +182,7 @@
                                if (ref === undefined) {
                                        ref = this._values.length;
                                        this._values.push(v);
+                                        console.log("value", v, "length", this._values.length);
                                        this._refs.set(v, ref);
                                }
                                let typeFlag = 0;

And it looks like _values in wasm_exec.js is bloating.

...
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 716
wasm_exec.js:185 value Arguments [6393.862, callee: (...), Symbol(Symbol.iterator): ƒ] length 717
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 718
wasm_exec.js:185 value Arguments [6410.528, callee: (...), Symbol(Symbol.iterator): ƒ] length 719
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 720
wasm_exec.js:185 value Arguments [6427.194, callee: (...), Symbol(Symbol.iterator): ƒ] length 721
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 722
wasm_exec.js:185 value Arguments [6443.86, callee: (...), Symbol(Symbol.iterator): ƒ] length 723
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 724
wasm_exec.js:185 value Arguments [6460.526, callee: (...), Symbol(Symbol.iterator): ƒ] length 725
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 726
wasm_exec.js:185 value Arguments [6477.192, callee: (...), Symbol(Symbol.iterator): ƒ] length 727
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 728
wasm_exec.js:185 value Arguments [6493.858, callee: (...), Symbol(Symbol.iterator): ƒ] length 729
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 730
wasm_exec.js:185 value Arguments [6510.524, callee: (...), Symbol(Symbol.iterator): ƒ] length 731
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 732
wasm_exec.js:185 value Arguments [6527.19, callee: (...), Symbol(Symbol.iterator): ƒ] length 733
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 734
wasm_exec.js:185 value Arguments [6543.856, callee: (...), Symbol(Symbol.iterator): ƒ] length 735
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 736
wasm_exec.js:185 value Arguments [6560.522, callee: (...), Symbol(Symbol.iterator): ƒ] length 737
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 738
wasm_exec.js:185 value Arguments [6577.188, callee: (...), Symbol(Symbol.iterator): ƒ] length 739
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 740
wasm_exec.js:185 value Arguments [6593.854, callee: (...), Symbol(Symbol.iterator): ƒ] length 741
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 742
wasm_exec.js:185 value Arguments [6610.52, callee: (...), Symbol(Symbol.iterator): ƒ] length 743
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 744
wasm_exec.js:185 value Arguments [6627.186, callee: (...), Symbol(Symbol.iterator): ƒ] length 745
wasm_exec.js:185 value {id: 1, this: undefined, args: Arguments(1)} length 746
...

[dmitshur]

/cc @neelance

[hajimehoshi]

What is 'Backlog'?

[dmitshur]

It's a recently introduced new milestone. Read about it in #34376.

[agnivade]

Yeah, it's a known issue and a marked TODO item in wasm_exec.js. From my investigation, it does not appear to be trivial. The stuff at wasm_exec side is simple though. Finalizing the ref from syscall/js side is where the problem lies.

Re-titling the issue to reflect that.

[hajimehoshi]

Thanks.

I understand GC is a TODO item, but besides, I was wondering what are the accumulated objects every frame (Arguments and objects including them).

[gopherbot]

Change https://golang.org/cl/203600 mentions this issue: syscall/js: garbage collect references to JavaScript values