go (original) (raw)

Please answer these questions before submitting your issue. Thanks!

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

go version go1.7.1 linux/amd64

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

GOARCH="amd64"
GOBIN="/home/cy/go/go-1.7.1/gopath/bin"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/cy/go/go-1.7.1/gopath"
GORACE=""
GOROOT="/home/cy/go/go-1.7.1"
GOTOOLDIR="/home/cy/go/go-1.7.1/pkg/tool/linux_amd64"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build525622235=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"

What did you do?

package main

import (
        "compress/flate"
        "fmt"
        "io/ioutil"
        "runtime"
        "runtime/debug"
)

const limit = 1024 * 16

func printss() {
        m := runtime.MemStats{}
        runtime.ReadMemStats(&m)
        fmt.Printf("inuse: %d sys: %d\n", m.StackInuse, m.StackSys)
}

func doflate() {
        z := make([]byte, limit*1000, limit*1000)
        fl, _ := flate.NewWriter(ioutil.Discard, 3)
        printss()
        fl.Write(z) // boom.
}

func main() {
        fmt.Println("hi")
        debug.SetMaxStack(limit) // comment out for more detail.
        doflate()                // boom.
        printss()
        runtime.GC()
        printss()
}

What did you expect to see?

Passing a large input to flate.Write() would not cause the stack to grow beyond the limit provided.

What did you see instead?

The stack grows very large.

Also, if I comment out this line:
debug.SetMaxStack(limit)

I get the following output:

hi
inuse: 393216 sys: 393216
inuse: 1474560 sys: 1474560
inuse: 950272 sys: 950272

Which suggests the runtime managed to shrink the stack a bit, but not nearly close enough to the original size.

Now imagine you have written a server that has lots of long running goroutines that occasionally compress a large blob. After introducing this code path, our stack usage increased ~10x.