x/net/http2: allow setting MaxConcurrentStreams on client #63196
Description
What version of Go are you using (go version)?
$ go version go version go1.19.13 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="/root/.cache/go-build" GOENV="/root/.config/go/env" GOEXE="" GOEXPERIMENT="" GOFLAGS="" GOHOSTARCH="amd64" GOHOSTOS="linux" GOINSECURE="" GOMODCACHE="/root/go/pkg/mod" GOOS="linux" GOPATH="/root/go" GOPROXY="https://proxy.golang.org,direct" GOROOT="/usr/local/go" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64" GOVCS="" GOVERSION="go1.19.13" GCCGO="gccgo" GOAMD64="v1" AR="ar" CC="gcc" CXX="g++" CGO_ENABLED="1" 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 -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build2198329798=/tmp/go-build -gno-record-gcc-switches"
What did you do?
I downloaded 9M files using 100 goroutines from http2.transport.
What did you expect to see?
There are currently more than 100 active streams in http2. I thought the connection would be newly opened, but it didn't.
What did you see instead?
After checking the http2.transport connection pool, we are reusing a single connection.
The netstat -nap check shows that there is 1 connection, rx full, tx full a lot.
The following modifications improve performance by creating connections in units of 20 active streams.
func (cc *ClientConn) State() ClientConnState {
cc.wmu.Lock()
maxConcurrent := cc.maxConcurrentStreams
if !cc.seenSettings {
maxConcurrent = 0
}
cc.wmu.Unlock()
+ // cc.mu.Lock()
+ // defer cc.mu.Unlock()
return ClientConnState{
Closed: cc.closed,
Closing: cc.closing || cc.singleUse || cc.doNotReuse || cc.goAway != nil,
StreamsActive: len(cc.streams),
StreamsReserved: cc.streamsReserved,
StreamsPending: cc.pendingRequests,
LastIdle: cc.lastIdle,
MaxConcurrentStreams: maxConcurrent,
}
}
func (cc *ClientConn) idleStateLocked() (st clientConnIdleState) {
if cc.singleUse && cc.nextStreamID > 1 {
return
}
var maxConcurrentOkay bool
if cc.t.StrictMaxConcurrentStreams {
// We'll tell the caller we can take a new request to
// prevent the caller from dialing a new TCP
// connection, but then we'll block later before
// writing it.
maxConcurrentOkay = true
} else {
maxConcurrentOkay = int64(len(cc.streams)+cc.streamsReserved+1) <= int64(cc.maxConcurrentStreams)
}
st.canTakeNewRequest = cc.goAway == nil && !cc.closed && !cc.closing && maxConcurrentOkay &&
!cc.doNotReuse &&
int64(cc.nextStreamID)+2*int64(cc.pendingRequests) < math.MaxInt32 &&
!cc.tooIdleLocked()
+ if st.canTakeNewRequest {
+ if cc.State().StreamsActive > 20 {
+ st.canTakeNewRequest = false
+ }
+ }
return
}As the number of active streams increases, http2 becomes slower and slower.