[lldb] [Core] Split read thread support into ThreadedCommunication

Split the read thread support from Communication into a dedicated
ThreadedCommunication subclass.  The read thread support is used only
by a subset of Communication consumers, and it adds a lot of complexity
to the base class.  Furthermore, having a dedicated subclass makes it
clear whether a particular consumer needs to account for the possibility
of read thread being running or not.

The modules currently calling `StartReadThread()` are updated to use
`ThreadedCommunication`.  The remaining modules use the simplified
`Communication` class.

`SBCommunication` is changed to use `ThreadedCommunication` in order
to avoid changing the public API.

`CommunicationKDP` is updated in order to (hopefully) compile with
the new code.  However, I do not have a Darwin box to test it, so I've
limited the changes to the bare minimum.

`GDBRemoteCommunication` is updated to become a `Broadcaster` directly.
Since it does not inherit from `ThreadedCommunication`, its event
support no longer collides with the one used for read thread and can
be implemented cleanly.  The support for
`eBroadcastBitReadThreadDidExit` is removed from the code -- since
the read thread was not used, this event was never reported.

Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.llvm.org/D133251

1 files changed, 0 insertions, 23 deletions

diff --git a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
index 37272d3..c0765dc 100644
--- a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
@@ -285,14 +285,6 @@ ProcessGDBRemote::ProcessGDBRemote(lldb::TargetSP target_sp,
               __FUNCTION__);
   }
 
-  const uint32_t gdb_event_mask = Communication::eBroadcastBitReadThreadDidExit;
-  if (m_async_listener_sp->StartListeningForEvents(
-          &m_gdb_comm, gdb_event_mask) != gdb_event_mask) {
-    LLDB_LOGF(log,
-              "ProcessGDBRemote::%s failed to listen for m_gdb_comm events",
-              __FUNCTION__);
-  }
-
   const uint64_t timeout_seconds =
       GetGlobalPluginProperties().GetPacketTimeout();
   if (timeout_seconds > 0)
@@ -3575,21 +3567,6 @@ thread_result_t ProcessGDBRemote::AsyncThread() {
           done = true;
           break;
         }
-      } else if (event_sp->BroadcasterIs(&m_gdb_comm)) {
-        switch (event_type) {
-        case Communication::eBroadcastBitReadThreadDidExit:
-          SetExitStatus(-1, "lost connection");
-          done = true;
-          break;
-
-        default:
-          LLDB_LOGF(log,
-                    "ProcessGDBRemote::%s(pid = %" PRIu64
-                    ") got unknown event 0x%8.8x",
-                    __FUNCTION__, GetID(), event_type);
-          done = true;
-          break;
-        }
       }
     } else {
       LLDB_LOGF(log,