x/playground: timeout running program but locally it works fine

[Ghilteras]

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

1.19 on playground

Does this issue reproduce with the latest release?

yes

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

locally where it works fine I use this

❯ go env                                                                                                                                                                ─╯
GO111MODULE="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/path/Library/Caches/go-build"
GOENV="/Users/path/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/path/go/pkg/mod"
GOOS="darwin"
GOPATH="/Users/path/go"
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/opt/go/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/opt/go/libexec/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.19.2"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
GOWORK=""
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/_w/9dtgqhsj1n13jrc_tcb_98pw0000gn/T/go-build3103171944=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

I run this playground https://go.dev/play/p/540B1xaqNzs

What did you expect to see?

I expect the program to run fine on Playground

What did you see instead?

Playground throws a weird timeout running program, but if I run it locally it works just fine.

[thanm]

@toothrot per owners.

Be advised that the playground runs program using a fake version of the time package, the idea being that if a program does a sleep for 10 seconds, we don't actually want to sleep for a real 10 seconds (that would be waste of playground resources). What this means in general is that programs that do complicated things with timers and time.Sleep calls are likely to encounter problems (as in your case here).

[Ghilteras]

@thanm @toothrot I understand so how can I make this example run if I cannot timeout? I've seen other playgrounds sleeping just fine, what's the complicated thing that playground cannot handle? Does this affect the Ticker as well?

[thanm]

A little more debugging:

$ rm -f issue57294
$ go build -tags=faketime issue57294.go
$ GODEBUG=tracebackancestors=10 \
  GOTRACEBACK=all \
   ./issue57294 1> faketime.err.txt 2>&1 &
$ PID=$!
$ sleep 5
$ kill -SEGV $PID

Seems that the program actually deadlocks, as opposed to just running slowly.

[Ghilteras]

@thanm I don't see any deadlocks locally, it compiles and runs just fine. I assume the deadlock is caused by faketime? How would I work around it?