[lldb] Add OS plugin property for reporting all threads (#123145)

Currently, an LLDB target option controls whether plugins report all
threads. However, it seems natural for this knowledge could come from
the plugin itself. To support this, this commits adds a virtual method
to the plugin base class, making the Python OS query the target option
to preserve existing behavior.

Author: felipepiovezan

lldb/include/lldb/Interpreter/Interfaces/OperatingSystemInterface.h

@@ -27,6 +27,8 @@ class OperatingSystemInterface : virtual public ScriptedThreadInterface {
   virtual std::optional<std::string> GetRegisterContextForTID(lldb::tid_t tid) {
     return std::nullopt;
   }
+
+  virtual std::optional<bool> DoesPluginReportAllThreads() { return {}; }
 };
 } // namespace lldb_private
 

lldb/include/lldb/Target/OperatingSystem.h

@@ -61,6 +61,8 @@ class OperatingSystem : public PluginInterface {
 
   virtual bool IsOperatingSystemPluginThread(const lldb::ThreadSP &thread_sp);
 
+  virtual bool DoesPluginReportAllThreads() = 0;
+
 protected:
   // Member variables.
   Process

lldb/source/Plugins/OperatingSystem/Python/OperatingSystemPython.cpp

@@ -386,4 +386,12 @@ lldb::ThreadSP OperatingSystemPython::CreateThread(lldb::tid_t tid,
   return ThreadSP();
 }
 
+bool OperatingSystemPython::DoesPluginReportAllThreads() {
+  // If the python plugin has a "DoesPluginReportAllThreads" method, use it.
+  if (std::optional<bool> plugin_answer =
+          m_operating_system_interface_sp->DoesPluginReportAllThreads())
+    return *plugin_answer;
+  return m_process->GetOSPluginReportsAllThreads();
+}
+
 #endif // #if LLDB_ENABLE_PYTHON

lldb/source/Plugins/OperatingSystem/Python/OperatingSystemPython.h

@@ -60,6 +60,8 @@ class OperatingSystemPython : public lldb_private::OperatingSystem {
   // Method for lazy creation of threads on demand
   lldb::ThreadSP CreateThread(lldb::tid_t tid, lldb::addr_t context) override;
 
+  bool DoesPluginReportAllThreads() override;
+
 protected:
   bool IsValid() const {
     return m_script_object_sp && m_script_object_sp->IsValid();

lldb/source/Plugins/ScriptInterpreter/Python/Interfaces/OperatingSystemPythonInterface.cpp

@@ -82,6 +82,16 @@ OperatingSystemPythonInterface::GetRegisterContextForTID(lldb::tid_t tid) {
   return obj->GetAsString()->GetValue().str();
 }
 
+std::optional<bool> OperatingSystemPythonInterface::DoesPluginReportAllThreads() {
+  Status error;
+  StructuredData::ObjectSP obj = Dispatch("does_plugin_report_all_threads", error);
+  if (!ScriptedInterface::CheckStructuredDataObject(LLVM_PRETTY_FUNCTION, obj,
+                                                    error))
+    return {};
+
+  return obj->GetAsBoolean()->GetValue();
+}
+
 void OperatingSystemPythonInterface::Initialize() {
   const std::vector<llvm::StringRef> ci_usages = {
       "settings set target.process.python-os-plugin-path <script-path>",

lldb/source/Plugins/ScriptInterpreter/Python/Interfaces/OperatingSystemPythonInterface.h

@@ -45,6 +45,8 @@ class OperatingSystemPythonInterface
 
   std::optional<std::string> GetRegisterContextForTID(lldb::tid_t tid) override;
 
+  std::optional<bool> DoesPluginReportAllThreads() override;
+
   static void Initialize();
 
   static void Terminate();

lldb/source/Target/Process.cpp

@@ -1182,7 +1182,7 @@ void Process::UpdateThreadListIfNeeded() {
           // See if the OS plugin reports all threads.  If it does, then
           // it is safe to clear unseen thread's plans here.  Otherwise we
           // should preserve them in case they show up again:
-          clear_unused_threads = GetOSPluginReportsAllThreads();
+          clear_unused_threads = os->DoesPluginReportAllThreads();
 
           // Turn off dynamic types to ensure we don't run any expressions.
           // Objective-C can run an expression to determine if a SBValue is a

lldb/source/Target/TargetProperties.td

@@ -223,7 +223,7 @@ let Definition = "process_experimental" in {
   def OSPluginReportsAllThreads: Property<"os-plugin-reports-all-threads", "Boolean">,
     Global,
     DefaultTrue,
-    Desc<"Set to False if your OS Plugins doesn't report all threads on each stop.">;
+    Desc<"Set to False if your Python OS Plugin doesn't report all threads on each stop.">;
 }
 
 let Definition = "process" in {

lldb/test/API/functionalities/plugins/python_os_plugin/stepping_plugin_threads/TestOSPluginStepping.py

@@ -40,11 +40,6 @@ def is_os_thread(self, thread):
     def run_python_os_step_missing_thread(self, do_prune):
         """Test that the Python operating system plugin works correctly"""
 
-        # Our OS plugin does NOT report all threads:
-        result = self.dbg.HandleCommand(
-            "settings set process.experimental.os-plugin-reports-all-threads false"
-        )
-
         python_os_plugin_path = os.path.join(self.getSourceDir(), "operating_system.py")
         (target, self.process, thread, thread_bkpt) = lldbutil.run_to_source_breakpoint(
             self, "first stop in thread - do a step out", self.main_file

lldb/test/API/functionalities/plugins/python_os_plugin/stepping_plugin_threads/operating_system.py

@@ -34,6 +34,9 @@ def __init__(self, process):
             if not self.g_value.IsValid():
                 print("Could not find g_value")
 
+    def does_plugin_report_all_threads(self):
+        return False
+
     def create_thread(self, tid, context):
         print("Called create thread with tid: ", tid)
         return None