Ensure races between pending and new SPDY streams don't violate session concurrency.

net/spdy/spdy_session.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/spdy/spdy_session.h"
 
 #include <algorithm>
 #include <map>
 
 #include "base/basictypes.h"
@@ skipping 808 matching lines @@
         max_concurrent_streams_ -
         (active_streams_.size() + created_streams_.size());
   }
   for (size_t i = 0;
        max_requests_to_process == 0 || i < max_requests_to_process; ++i) {
     base::WeakPtr<SpdyStreamRequest> pending_request =
         GetNextPendingStreamRequest();
     if (!pending_request)
       break;
 
+    // Note that this post can race with other stream creations, and it's
+    // possible that the un-stalled stream will be stalled again if it loses.
+    // TODO(jgraettinger): Provide stronger ordering guarantees.
     base::MessageLoop::current()->PostTask(
         FROM_HERE,
         base::Bind(&SpdySession::CompleteStreamRequest,
                    weak_factory_.GetWeakPtr(),
                    pending_request));
   }
 }
 
 void SpdySession::AddPooledAlias(const SpdySessionKey& alias_key) {
   pooled_aliases_.insert(alias_key);
@@ skipping 2014 matching lines @@
   }
 }
 
 void SpdySession::CompleteStreamRequest(
     const base::WeakPtr<SpdyStreamRequest>& pending_request) {
   // Abort if the request has already been cancelled.
   if (!pending_request)
     return;
 
   base::WeakPtr<SpdyStream> stream;
-  int rv = CreateStream(*pending_request, &stream);
+  int rv = TryCreateStream(pending_request, &stream);
 
   if (rv == OK) {

[Ryan Hamilton, 2014/05/19 23:00:07]

How 'bout early return here:

if (rv == OK) {
  DCHECK(stream);
  pending_request->OnRequestCompleteSuccess(stream);
  return;
}

DCHECK(!stream);
if (rv != ERR_IO_PENDING)
  pending_request->OnRequestCompleteFailure(rv);

[Johnny, 2014/05/19 23:37:32]

Done.

     DCHECK(stream);
     pending_request->OnRequestCompleteSuccess(stream);
+  } else if (rv == ERR_IO_PENDING) {
+    DCHECK(!stream);
   } else {
     DCHECK(!stream);
     pending_request->OnRequestCompleteFailure(rv);
   }
 }
 
 SSLClientSocket* SpdySession::GetSSLClientSocket() const {
   if (!is_secure_)
     return NULL;
   SSLClientSocket* ssl_socket =
@@ skipping 191 matching lines @@
     if (!queue->empty()) {
       SpdyStreamId stream_id = queue->front();
       queue->pop_front();
       return stream_id;
     }
   }
   return 0;
 }
 
 }  // namespace net