Closed
Description
What version of Go are you using (go version
)?
$ go version go version go1.15.2 linux/amd64
Does this issue reproduce with the latest release?
yes
What operating system and processor architecture are you using (go env
)?
go env
Output
$ go env GO111MODULE="" GOARCH="amd64" GOBIN="" GOCACHE="/home/hiroaki-m/.cache/go-build" GOENV="/home/hiroaki-m/.config/go/env" GOEXE="" GOFLAGS="" GOHOSTARCH="amd64" GOHOSTOS="linux" GOINSECURE="" GOMODCACHE="/home/hiroaki-m/go/pkg/mod" GONOPROXY="" GONOSUMDB="" GOOS="linux" GOPATH="/home/hiroaki-m/go" GOPRIVATE="" GOPROXY="https://proxy.golang.org,direct" GOROOT="/usr/local/go" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64" GCCGO="gccgo" AR="ar" CC="gcc" CXX="g++" CGO_ENABLED="1" GOMOD="" 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-build121864325=/tmp/go-build -gno-record-gcc-switches"
What did you do?
package main
import (
"context"
"fmt"
"net/http"
"net/http/httptest"
)
type handler struct{}
func (h handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
w.Header().Add("Content-Length", "0")
}
func requestAndCancel(url string) {
for {
wait := make(chan struct{})
done := make(chan struct{})
ctx, cancel := context.WithCancel(context.Background())
req, _ := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
go func() {
close(wait)
http.DefaultTransport.RoundTrip(req)
close(done)
}()
<-wait
cancel()
<-done
}
}
func main() {
ts := httptest.NewServer(&handler{})
defer ts.Close()
http.DefaultTransport.(*http.Transport).MaxConnsPerHost = 1
// request and cancel
for i := 0; i < 8; i++ {
go requestAndCancel(ts.URL)
}
// request only
for {
req, _ := http.NewRequest(http.MethodGet, ts.URL, nil)
if _, err := http.DefaultTransport.RoundTrip(req); err != nil {
fmt.Printf("An unexpected error has occurred: %#v\n", err)
break
}
}
}
I'm gussing that the keep-alived tcp connection is used simultaneously by multiple goroutine.
Early return to connection pool https://go.googlesource.com/go/+/refs/tags/go1.15.2/src/net/http/transport.go#2089
What did you expect to see?
No error response and loop infinity.
What did you see instead?
$ date -u; go run context_cancel_race.go ; date -u
Thu 24 Sep 2020 03:28:55 AM UTC
An unexpected error has occurred: &errors.errorString{s:"context canceled"}
Thu 24 Sep 2020 03:30:00 AM UTC