[lldb] Speculative fix to TestGuiExpandThreadsTree

This test relies on being able to unwind from an arbitrary place inside
libc. While I am not sure this is the cause of the observed flakyness,
it is known that we are not able to unwind correctly from some places in
(linux) libc.

This patch adds additional synchronization to ensure that the inferior
is in the main function (instead of pthread guts) when lldb tries to
unwind it. At the very least, it should make the test runs more
predictable/repeatable.

lldb/test/API/commands/gui/expand-threads-tree/Makefile

@@ -1,3 +1,3 @@
-C_SOURCES := main.c
+CXX_SOURCES := main.cpp
 ENABLE_THREADS := YES
 include Makefile.rules

lldb/test/API/commands/gui/expand-threads-tree/TestGuiExpandThreadsTree.py

@@ -22,7 +22,7 @@ class TestGuiExpandThreadsTree(PExpectTest):
         self.build()
 
         self.launch(executable=self.getBuildArtifact("a.out"), dimensions=(100,500))
-        self.expect("breakpoint set -r thread_start_routine", substrs=["Breakpoint 1", "address ="])
+        self.expect("breakpoint set -n break_here", substrs=["Breakpoint 1", "address ="])
         self.expect("run", substrs=["stop reason ="])
 
         escape_key = chr(27).encode()
@@ -33,7 +33,7 @@ class TestGuiExpandThreadsTree(PExpectTest):
         self.child.expect_exact("Threads")
 
         # The thread running thread_start_routine should be expanded.
-        self.child.expect_exact("frame #0: thread_start_routine")
+        self.child.expect_exact("frame #0: break_here")
 
         # Exit GUI.
         self.child.send(escape_key)

lldb/test/API/commands/gui/expand-threads-tree/main.c

@@ -1,10 +0,0 @@
-#include <pthread.h>
-
-void *thread_start_routine(void *arg) { return NULL; }
-
-int main() {
-  pthread_t thread;
-  pthread_create(&thread, NULL, thread_start_routine, NULL);
-  pthread_join(thread, NULL);
-  return 0;
-}

lldb/test/API/commands/gui/expand-threads-tree/main.cpp

@@ -0,0 +1,24 @@
+#include "pseudo_barrier.h"
+#include <thread>
+
+
+pseudo_barrier_t barrier_before;
+pseudo_barrier_t barrier_after;
+
+void break_here() {}
+
+void thread_func() {
+    pseudo_barrier_wait(barrier_before);
+    break_here();
+    pseudo_barrier_wait(barrier_after);
+}
+
+int main() {
+  pseudo_barrier_init(barrier_before, 2);
+  pseudo_barrier_init(barrier_after, 2);
+  std::thread thread(thread_func);
+  pseudo_barrier_wait(barrier_before);
+  pseudo_barrier_wait(barrier_after);
+  thread.join();
+  return 0;
+}