Rewriting TestMultithreaded.py to solve flakyness on Linux

[ravitheja]

Summary

test_listener_event_process_state checks for Threads
and Frames in the multithreaded_queue. The listener_func has
more computational load, which may be latter executed than the
pop leading to the failure. This patch tries to only check for
frames in listener_func as presence of frames also confirms
prescence of threads and avoids the second push into the
multithreaded_queue.

[labath]

I am somewhat surprised that this solves anything (I mean, you claim that the problem is the ordering between the push and pop, but I don't see how this could change that ordering). If the problem was that the check_listener was not waiting long enough, then it should be sufficient to increase the timeout...

That said, I don't think it should make things any worse either, so I'm ready to give it a go...

[ravitheja]

@labath, Well the other tests in TestMultithreaded.py are not flaky and I see the only difference as an extra push operation, so I thought the push operation could be potential bottleneck.

packages/Python/lldbsuite/test/api/multithreaded/TestMultithreaded.py

def test_sb_api_listener_event_description(self):
         self.build_and_test('driver.cpp listener_test.cpp test_listener_event_description.cpp',
                             'test_listener_event_description')
         pass
 
     @skipIfRemote
     @skipIfNoSBHeaders
     @skipIfWindows # clang-cl does not support throw or catch (llvm.org/pr24538)
     @expectedFlakeyFreeBSD
-    @expectedFlakeyLinux # Driver occasionally returns '1' as exit status
     @expectedFailureAll("llvm.org/pr23139", oslist=["linux"], compiler="gcc", compiler_version=[">=","4.9"], archs=["x86_64"])
     def test_sb_api_listener_event_process_state(self):
         """ Test that a registered SBListener receives events when a process
             changes state.
         """
         self.build_and_test('driver.cpp listener_test.cpp test_listener_event_process_state.cpp',
                             'test_listener_event_process_state')
         pass

packages/Python/lldbsuite/test/api/multithreaded/test_listener_event_process_state.cpp

 #include "common.h"
 
 using namespace lldb;
 using namespace std;
 
 // listener thread control
 extern atomic<bool> g_done;
 
-multithreaded_queue<string> g_thread_descriptions;
 multithreaded_queue<string> g_frame_functions;
 
 extern SBListener g_listener;
 
 void listener_func() {
   while (!g_done) {
     SBEvent event;
     bool got_event = g_listener.WaitForEvent(1, event);
     if (got_event) {
       if (!event.IsValid())
         throw Exception("event is not valid in listener thread");
-
         // send process description
         SBProcess process = SBProcess::GetProcessFromEvent(event);
         SBStream description;
 
         for (int i = 0; i < process.GetNumThreads(); ++i) {
             // send each thread description
-        description.Clear();
             SBThread thread = process.GetThreadAtIndex(i);
-        thread.GetDescription(description);
-        g_thread_descriptions.push(description.GetData());
-
             // send each frame function name
             uint32_t num_frames = thread.GetNumFrames();
             for(int j = 0; j < num_frames; ++j) {
                 const char* function_name = thread.GetFrameAtIndex(j).GetSymbol().GetName();
                 if (function_name)
-            g_frame_functions.push(function_name);
+                    g_frame_functions.push(string(function_name));
             }
         }
     }
   }
 }
 
 void check_listener(SBDebugger &dbg) {
   // check thread description
   bool got_description = false;
-  string desc = g_thread_descriptions.pop(5, got_description);
-  if (!got_description)
-    throw Exception("Expected at least one thread description string");
-
-  // check at least one frame has a function name
-  desc = g_frame_functions.pop(5, got_description);
-  if (!got_description)
-    throw Exception("Expected at least one frame function name string");
+  string func_name = g_frame_functions.pop(5, got_description);
+  
+  if(got_description == false)
+    throw Exception("Expected at least one frame function");
 }