runtime: cgo program with select {} hangs

[alexbrainman]

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

go version devel +65c365b Wed May 23 23:51:30 2018 +0000 linux/amd64

Does this issue reproduce with the latest release?

yes

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

GOARCH="amd64"
GOBIN=""
GOCACHE="/home/a/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/a"
GORACE=""
GOROOT="/home/a/go"
GOTMPDIR=""
GOTOOLDIR="/home/a/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
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 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build476325891=/tmp/go-build -gno-record-gcc-switches"

What did you do?

$ cat main.go
package main

import "C"

func main() {
select {}
}
$ go build -o a && ./a

What did you expect to see?

fatal error: all goroutines are asleep - deadlock!
...

similar to what program above does without import "C".

What did you see instead?

My program hangs.

This was discovered #6751 (comment) by @billziss-gh in the search for solution for issue #6751.

/cc @aclements and @ianlancetaylor

I am not sure if this is a bug or not, so looking for advice.

Alex

[ianlancetaylor]

The deadlock detector doesn't work for programs that use cgo, and never has. I would call this a bug, but it's low priority and hard to fix.

[aclements]

Is this even possible to fix? The C code could have started threads that the Go runtime isn't aware of, so the process could still be making progress even if no goroutines are runnable and there are no calls from Go into C.

[rsc]

I agree with Austin. This program might just be a shell to let C threads execute. There's no way to know.