[Lldb-commits] [lldb] Refactor `ThreadList::WillResume()` to prepare to support reverse execution (PR #120817)

[via lldb-commits]

================
@@ -582,31 +531,92 @@ bool ThreadList::WillResume() {
   // There are two special kinds of thread that have priority for "StopOthers":
   // a "ShouldRunBeforePublicStop thread, or the currently selected thread.  If
   // we find one satisfying that critereon, put it here.
-  ThreadSP stop_others_thread_sp;
-
+  ThreadSP thread_to_run;
   for (pos = m_threads.begin(); pos != end; ++pos) {
     ThreadSP thread_sp(*pos);
     if (thread_sp->GetResumeState() != eStateSuspended &&
         thread_sp->GetCurrentPlan()->StopOthers()) {
-      if ((*pos)->IsOperatingSystemPluginThread() &&
-          !(*pos)->GetBackingThread())
+      if (thread_sp->IsOperatingSystemPluginThread() &&
+          !thread_sp->GetBackingThread())
         continue;
 
       // You can't say "stop others" and also want yourself to be suspended.
       assert(thread_sp->GetCurrentPlan()->RunState() != eStateSuspended);
       run_me_only_list.AddThread(thread_sp);
 
       if (thread_sp == GetSelectedThread())
-        stop_others_thread_sp = thread_sp;
-        
+        thread_to_run = thread_sp;
+
       if (thread_sp->ShouldRunBeforePublicStop()) {
         // This takes precedence, so if we find one of these, service it:
-        stop_others_thread_sp = thread_sp;
+        thread_to_run = thread_sp;
         break;
       }
     }
   }
 
+  if (run_me_only_list.GetSize(false) > 0 && !thread_to_run) {
+    if (run_me_only_list.GetSize(false) == 1) {
+      thread_to_run = run_me_only_list.GetThreadAtIndex(0);
+    } else {
+      int random_thread =
+          (int)((run_me_only_list.GetSize(false) * (double)rand()) /
+                (RAND_MAX + 1.0));
+      thread_to_run = run_me_only_list.GetThreadAtIndex(random_thread);
+    }
+  }
+
+  // Give all the threads that are likely to run a last chance to set up their
+  // state before we negotiate who is actually going to get a chance to run...
+  // Don't set to resume suspended threads, and if any thread wanted to stop
+  // others, only call setup on the threads that request StopOthers...
+  bool wants_solo_run = run_me_only_list.GetSize(false) > 0;
+  for (pos = m_threads.begin(); pos != end; ++pos) {
+    ThreadSP thread_sp(*pos);
+    // See if any thread wants to run stopping others.  If it does, then we
+    // won't setup the other threads for resume, since they aren't going to get
+    // a chance to run.  This is necessary because the SetupForResume might add
+    // "StopOthers" plans which would then get to be part of the who-gets-to-run
+    // negotiation, but they're coming in after the fact, and the threads that
+    // are already set up should take priority.
+    if (thread_sp->GetResumeState() != eStateSuspended &&
+        (!wants_solo_run || (*pos)->GetCurrentPlan()->StopOthers())) {
+      if (thread_sp->IsOperatingSystemPluginThread() &&
+          !thread_sp->GetBackingThread())
+        continue;
+      if (thread_sp->SetupForResume()) {
+        // You can't say "stop others" and also want yourself to be suspended.
+        assert(thread_sp->GetCurrentPlan()->RunState() != eStateSuspended);
+        run_me_only_list.AddThread(thread_sp);
----------------
jimingham wrote:

Why does this do any good?  You didn't clear the list, and you aren't going to add threads here that didn't get added in the first loop.  So you're just adding them twice.

https://github.com/llvm/llvm-project/pull/120817