[lldb] [llgs] Send process output asynchronously in non-stop mode

Introduce a new %Stdio notification category and use it to send process
output asynchronously when running in non-stop mode.  This is an LLDB
extension since GDB does not use the 'O' packet for process output,
just for replies to 'qRcmd' packets.

Using the async notification mechanism implies that only the first
output packet is sent immediately to the client.  The client needs
to request subsequent notifications (if any) using the new vStdio packet
(that works pretty much like vStopped for the Stop notification queue).

The packet handler in lldb-server tests is updated to handle the async
stdio packets in addition to the regular O packets.  However, due
to the implications noted above, it can only handle the first output
packet sent by the server.  Subsequent packets need to be explicitly
requested via vStdio.

Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.llvm.org/D128849

1 files changed, 31 insertions, 13 deletions

diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp
index 8edb49f..49f37ba 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunicationServerLLGS.cpp
@@ -246,6 +246,9 @@ void GDBRemoteCommunicationServerLLGS::RegisterPacketHandlers() {
       StringExtractorGDBRemote::eServerPacketType_QNonStop,
       &GDBRemoteCommunicationServerLLGS::Handle_QNonStop);
   RegisterMemberFunctionHandler(
+      StringExtractorGDBRemote::eServerPacketType_vStdio,
+      &GDBRemoteCommunicationServerLLGS::Handle_vStdio);
+  RegisterMemberFunctionHandler(
       StringExtractorGDBRemote::eServerPacketType_vStopped,
       &GDBRemoteCommunicationServerLLGS::Handle_vStopped);
   RegisterMemberFunctionHandler(
@@ -1192,6 +1195,9 @@ GDBRemoteCommunicationServerLLGS::SendONotification(const char *buffer,
   response.PutChar('O');
   response.PutBytesAsRawHex8(buffer, len);
 
+  if (m_non_stop)
+    return SendNotificationPacketNoLock("Stdio", m_stdio_notification_queue,
+                                        response.GetString());
   return SendPacketNoLock(response.GetString());
 }
 
@@ -3907,26 +3913,38 @@ GDBRemoteCommunicationServerLLGS::Handle_QNonStop(
 }
 
 GDBRemoteCommunication::PacketResult
-GDBRemoteCommunicationServerLLGS::Handle_vStopped(
-    StringExtractorGDBRemote &packet) {
+GDBRemoteCommunicationServerLLGS::HandleNotificationAck(
+    std::deque<std::string> &queue) {
   // Per the protocol, the first message put into the queue is sent
-  // immediately.  However, it remains the queue until the client ACKs
-  // it via vStopped -- then we pop it and send the next message.
-  // The process repeats until the last message in the queue is ACK-ed,
-  // in which case the vStopped packet sends an OK response.
-
-  if (m_stop_notification_queue.empty())
+  // immediately.  However, it remains the queue until the client ACKs it --
+  // then we pop it and send the next message.  The process repeats until
+  // the last message in the queue is ACK-ed, in which case the packet sends
+  // an OK response.
+  if (queue.empty())
     return SendErrorResponse(Status("No pending notification to ack"));
-  m_stop_notification_queue.pop_front();
-  if (!m_stop_notification_queue.empty())
-    return SendPacketNoLock(m_stop_notification_queue.front());
+  queue.pop_front();
+  if (!queue.empty())
+    return SendPacketNoLock(queue.front());
+  return SendOKResponse();
+}
+
+GDBRemoteCommunication::PacketResult
+GDBRemoteCommunicationServerLLGS::Handle_vStdio(
+    StringExtractorGDBRemote &packet) {
+  return HandleNotificationAck(m_stdio_notification_queue);
+}
+
+GDBRemoteCommunication::PacketResult
+GDBRemoteCommunicationServerLLGS::Handle_vStopped(
+    StringExtractorGDBRemote &packet) {
+  PacketResult ret = HandleNotificationAck(m_stop_notification_queue);
   // If this was the last notification and all the processes exited,
   // terminate the server.
-  if (m_debugged_processes.empty()) {
+  if (m_stop_notification_queue.empty() && m_debugged_processes.empty()) {
     m_exit_now = true;
     m_mainloop.RequestTermination();
   }
-  return SendOKResponse();
+  return ret;
 }
 
 GDBRemoteCommunication::PacketResult