http2: fix leak in activeRes by removing activeRes

AFAICT, activeRes serves no real purpose. It is used in just two ways:

- To reduce the number of calls to closeIfIdle, which reduces the number
  of acquires of cc.mu when there are many concurrent streams. I dug
  through the CL history and could not find any benchmarks showing that
  this is necessary.

- To avoid redundant calls to cs.bufPipe.CloseWithError(err) when a read
  loop is shutdown. This is unnecessary, since redundant CloseWithError
  calls are ignored.

Since there isn't a good reason to have activeRes, the simplest way to
fix the leak is to remove activeRes entirely.

Updates golang/go#21543

Change-Id: I1d1d2dc6c946425a2772c8bf71436707021ac269
Reviewed-on: https://go-review.googlesource.com/80137Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

http2/transport.go

@@ -1376,17 +1376,12 @@ func (cc *ClientConn) streamByID(id uint32, andRemove bool) *clientStream {
 // clientConnReadLoop is the state owned by the clientConn's frame-reading readLoop.
 type clientConnReadLoop struct {
 	cc            *ClientConn
-	activeRes     map[uint32]*clientStream // keyed by streamID
 	closeWhenIdle bool
 }
 
 // readLoop runs in its own goroutine and reads and dispatches frames.
 func (cc *ClientConn) readLoop() {
-	rl := &clientConnReadLoop{
-		cc:        cc,
-		activeRes: make(map[uint32]*clientStream),
-	}
-
+	rl := &clientConnReadLoop{cc: cc}
 	defer rl.cleanup()
 	cc.readerErr = rl.run()
 	if ce, ok := cc.readerErr.(ConnectionError); ok {
@@ -1441,10 +1436,8 @@ func (rl *clientConnReadLoop) cleanup() {
 	} else if err == io.EOF {
 		err = io.ErrUnexpectedEOF
 	}
-	for _, cs := range rl.activeRes {
-		cs.bufPipe.CloseWithError(err)
-	}
 	for _, cs := range cc.streams {
+		cs.bufPipe.CloseWithError(err) // no-op if already closed
 		select {
 		case cs.resc <- resAndError{err: err}:
 		default:
@@ -1522,7 +1515,7 @@ func (rl *clientConnReadLoop) run() error {
 			}
 			return err
 		}
-		if rl.closeWhenIdle && gotReply && maybeIdle && len(rl.activeRes) == 0 {
+		if rl.closeWhenIdle && gotReply && maybeIdle {
 			cc.closeIfIdle()
 		}
 	}
@@ -1578,9 +1571,6 @@ func (rl *clientConnReadLoop) processHeaders(f *MetaHeadersFrame) error {
 		// (nil, nil) special case. See handleResponse docs.
 		return nil
 	}
-	if res.Body != noBody {
-		rl.activeRes[cs.ID] = cs
-	}
 	cs.resTrailer = &res.Trailer
 	cs.resc <- resAndError{res: res}
 	return nil
@@ -1919,7 +1909,6 @@ func (rl *clientConnReadLoop) endStreamError(cs *clientStream, err error) {
 		rl.closeWhenIdle = true
 	}
 	cs.bufPipe.closeWithErrorAndCode(err, code)
-	delete(rl.activeRes, cs.ID)
 
 	select {
 	case cs.resc <- resAndError{err: err}:
@@ -2046,7 +2035,6 @@ func (rl *clientConnReadLoop) processResetStream(f *RSTStreamFrame) error {
 		cs.bufPipe.CloseWithError(err)
 		cs.cc.cond.Broadcast() // wake up checkResetOrDone via clientStream.awaitFlowControl
 	}
-	delete(rl.activeRes, cs.ID)
 	return nil
 }