Optionally defer responding to a QUIC ACK until all ACK processing has completed for an EpollServer…

net/quic/quic_connection.cc

Index: net/quic/quic_connection.cc
diff --git a/net/quic/quic_connection.cc b/net/quic/quic_connection.cc
index 46636fae13f9e6ec0be2b186b3a860d950578baa..75640a3fd9dd6a3658b6d6b4d3928a9883c32fb3 100644
--- a/net/quic/quic_connection.cc
+++ b/net/quic/quic_connection.cc
@@ -129,7 +129,7 @@ class SendAlarm : public QuicAlarm::Delegate {
   explicit SendAlarm(QuicConnection* connection) : connection_(connection) {}
 
   QuicTime OnAlarm() override {
-    connection_->WriteIfNotBlocked();
+    connection_->WriteAndBundleAcksIfNotBlocked();
     // Never reschedule the alarm, since CanWrite does that.
     return QuicTime::Zero();
   }
@@ -284,6 +284,7 @@ QuicConnection::QuicConnection(QuicConnectionId connection_id,
       ack_mode_(TCP_ACKING),
       delay_setting_retransmission_alarm_(false),
       pending_retransmission_alarm_(false),
+      defer_send_in_response_to_packets_(false),
       arena_(),
       ack_alarm_(helper->CreateAlarm(arena_.New<AckAlarm>(this), &arena_)),
       retransmission_alarm_(
@@ -1135,11 +1136,14 @@ void QuicConnection::MaybeSendInResponseToPacket() {
   if (!connected_) {
     return;
   }
-  ScopedPacketBundler bundler(this, ack_queued_ ? SEND_ACK : NO_ACK);
-
   // Now that we have received an ack, we might be able to send packets which
   // are queued locally, or drain streams which are blocked.
-  WriteIfNotBlocked();
+  if (defer_send_in_response_to_packets_) {
+    send_alarm_->Cancel();
+    send_alarm_->Set(clock_->ApproximateNow());
+  } else {
+    WriteAndBundleAcksIfNotBlocked();
+  }
 }
 
 void QuicConnection::SendVersionNegotiationPacket() {
@@ -1400,6 +1404,13 @@ void QuicConnection::WriteIfNotBlocked() {
   }
 }
 
+void QuicConnection::WriteAndBundleAcksIfNotBlocked() {
+  if (!writer_->IsWriteBlocked()) {
+    ScopedPacketBundler bundler(this, ack_queued_ ? SEND_ACK : NO_ACK);
+    OnCanWrite();
+  }
+}
+
 bool QuicConnection::ProcessValidatedPacket(const QuicPacketHeader& header) {
   if (FLAGS_check_peer_address_change_after_decryption) {
     if (perspective_ == Perspective::IS_SERVER &&