Please answer these questions before submitting your issue. Thanks!

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

1.8.1

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

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/drgomesp/go"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.8/libexec"
GOTOOLDIR="/usr/local/Cellar/go/1.8/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/7j/l9t66rwd06d64lrgffpbct1m0000gn/T/go-build463779310=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

I have a simple implementation that uses context.WithTimeout, more or less like:

ctx, cancelFn := context.WithTimeout(context.Background(), time.Duration(time.Minute*1))
defer cancelFn()

select {
    case <-ctx.Done():
        // ...
        return
}

When I monitor the number of currently existing goroutines (using runtime.NumGoroutines()), it seems that whenever the WithTimeout() function gets called, it internally creates a goroutine to keep track of the time and eventually cancel the context (which makes sense, if you look at the internals (https://github.com/golang/go/blob/master/src/context/context.go#L401 and https://github.com/golang/go/blob/master/src/time/sleep.go#L170).

However, when the context is finished and the case statement is reached, the goroutine is not being released. It seems that it keeps running forever and the resources are not released properly.

If I change the implementation to use a simpler version of a timeout, without the context.WithTimeout(), more or less like:

select {
    case <-time.After(time.Minute*1):
        // ...
        return
}

Then the number of goroutines is the expected in the first place and nothing seems to leak.

What could be the problem? What am I missing?

What did you expect to see?

Expect the goroutine created internally to be released

What did you see instead?

Seems that the goroutine created internally is never released