x/mobile/cmd/gomobile: iOS app built with gomobile-build freezes after switching apps

[hajimehoshi]

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

go version go1.10 darwin/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="/Users/hajimehoshi/Library/Caches/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/hajimehoshi/go"
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/7t/qw3np69559591s1v0mk5_p1m0000gn/T/go-build572694656=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

1. gomobile build -target=ios -bundleid=com.hajimehoshi.gomobiletest -work golang.org/x/mobile/example/basic
2. Open the Xcode project in the work directory
3. Fix the singing to be able to install the app
4. Install and run the 'basic' app
5. Try to switch to another app and go back to the basic app

What did you expect to see?

The app continues to run

What did you see instead?

The app freezes

[hajimehoshi]

CC @eliasnaur