[lldb-dap] Client expects initial threads request not empty

Author: kusmour

lldb/packages/Python/lldbsuite/test/tools/lldb-dap/dap_server.py

@@ -649,6 +649,10 @@ def request_configurationDone(self):
         response = self.send_recv(command_dict)
         if response:
             self.configuration_done_sent = True
+            # Client requests the baseline of currently existing threads after
+            # a successful launch or attach.
+            # Kick off the threads request that follows
+            self.request_threads()
         return response
 
     def _process_stopped(self):

lldb/tools/lldb-dap/DAP.h

@@ -207,6 +207,9 @@ struct DAP {
   /// The set of features supported by the connected client.
   llvm::DenseSet<ClientFeature> clientFeatures;
 
+  /// The initial thread list upon attaching
+  std::optional<llvm::json::Array> initial_thread_list;
+
   /// Creates a new DAP sessions.
   ///
   /// \param[in] log

lldb/tools/lldb-dap/Handler/ConfigurationDoneRequestHandler.cpp

@@ -44,6 +44,7 @@ namespace lldb_dap {
 //             just an acknowledgement, so no body field is required."
 //             }]
 // },
+
 void ConfigurationDoneRequestHandler::operator()(
     const llvm::json::Object &request) const {
   llvm::json::Object response;
@@ -52,8 +53,15 @@ void ConfigurationDoneRequestHandler::operator()(
   dap.configuration_done_sent = true;
   if (dap.stop_at_entry)
     SendThreadStoppedEvent(dap);
-  else
+  else {
+    // Client requests the baseline of currently existing threads after
+    // a successful launch or attach by sending a 'threads' request
+    // right after receiving the configurationDone response.
+    // Obtain the list of threads before we resume the process
+    dap.initial_thread_list =
+        GetThreads(dap.target.GetProcess(), dap.thread_format);
     dap.target.GetProcess().Continue();
+  }
 }
 
 } // namespace lldb_dap

lldb/tools/lldb-dap/Handler/ThreadsRequestHandler.cpp

@@ -50,16 +50,22 @@ namespace lldb_dap {
 // }
 void ThreadsRequestHandler::operator()(
     const llvm::json::Object &request) const {
-  lldb::SBProcess process = dap.target.GetProcess();
   llvm::json::Object response;
   FillResponse(request, response);
 
-  const uint32_t num_threads = process.GetNumThreads();
   llvm::json::Array threads;
-  for (uint32_t thread_idx = 0; thread_idx < num_threads; ++thread_idx) {
-    lldb::SBThread thread = process.GetThreadAtIndex(thread_idx);
-    threads.emplace_back(CreateThread(thread, dap.thread_format));
-  }
+  // Client requests the baseline of currently existing threads after
+  // a successful launch or attach by sending a 'threads' request
+  // right after receiving the configurationDone response.
+  // If no thread has reported to the client, it prevents something
+  // like the pause request from working in the running state.
+  // Return the cache of initial threads as the process might have resumed
+  if (dap.initial_thread_list) {
+    threads = dap.initial_thread_list.value();
+    dap.initial_thread_list.reset();
+  } else
+    threads = GetThreads(dap.target.GetProcess(), dap.thread_format);
+
   if (threads.size() == 0) {
     response["success"] = llvm::json::Value(false);
   }

lldb/tools/lldb-dap/JSONUtils.cpp

@@ -870,6 +870,16 @@ llvm::json::Value CreateThread(lldb::SBThread &thread, lldb::SBFormat &format) {
   return llvm::json::Value(std::move(object));
 }
 
+llvm::json::Array GetThreads(lldb::SBProcess process, lldb::SBFormat &format) {
+  llvm::json::Array threads;
+  const uint32_t num_threads = process.GetNumThreads();
+  for (uint32_t thread_idx = 0; thread_idx < num_threads; ++thread_idx) {
+    lldb::SBThread thread = process.GetThreadAtIndex(thread_idx);
+    threads.emplace_back(CreateThread(thread, format));
+  }
+  return threads;
+}
+
 // "StoppedEvent": {
 //   "allOf": [ { "$ref": "#/definitions/Event" }, {
 //     "type": "object",

lldb/tools/lldb-dap/JSONUtils.h

@@ -414,6 +414,8 @@ llvm::json::Value CreateExtendedStackFrameLabel(lldb::SBThread &thread,
 ///     definition outlined by Microsoft.
 llvm::json::Value CreateThread(lldb::SBThread &thread, lldb::SBFormat &format);
 
+llvm::json::Array GetThreads(lldb::SBProcess process, lldb::SBFormat &format);
+
 /// Create a "StoppedEvent" object for a LLDB thread object.
 ///
 /// This function will fill in the following keys in the returned