Fix multi-thread resume when in-process debug adapter is used

Per the DAP spec, a ContinueRequest should resume all threads unless
singleThread=True is explicitly set. Previously, only the out-of-process
adapter path worked correctly (it transformed threadId to '*' before
forwarding to pydevd). With the in-process adapter, the specific threadId
reached pydevd directly but was only used to resume that one thread.

Fix on_continue_request to set thread_id='*' whenever singleThread is not
True, regardless of multi_threads_single_notification. Also update
write_continue test helper and add a regression test.

Fixes: #2009

Co-authored-by: rchiodo <19672699+rchiodo@users.noreply.github.com>

Author: Copilot

src/debugpy/_vendored/pydevd/_pydevd_bundle/pydevd_process_net_command_json.py

@@ -559,7 +559,13 @@ def on_continue_request(self, py_db, request):
         """
         arguments = request.arguments  # : :type arguments: ContinueArguments
         thread_id = arguments.threadId
-        if py_db.multi_threads_single_notification:
+
+        # Per the DAP spec, the continue request resumes execution of all threads
+        # unless singleThread is explicitly true (and the capability
+        # supportsSingleThreadExecutionRequests is advertised). Only use the
+        # specific threadId when singleThread is set; otherwise resume all.
+        single_thread = arguments.singleThread
+        if not single_thread or py_db.multi_threads_single_notification:
             thread_id = "*"
 
         def on_resumed():

src/debugpy/_vendored/pydevd/tests_python/resources/_debugger_case_multi_threads_continue.py

@@ -0,0 +1,25 @@
+"""
+Test for verifying that continuing from a breakpoint resumes all threads,
+not just the thread that hit the breakpoint.
+
+When a specific threadId is sent in the ContinueRequest without singleThread=True,
+all threads should be resumed per the DAP spec.
+"""
+import threading
+
+stop_event = threading.Event()
+
+
+def thread_func():
+    stop_event.wait()  # Thread 2 line - wait until signaled
+    print("Thread finished")
+
+
+if __name__ == "__main__":
+    t = threading.Thread(target=thread_func)
+    t.start()
+
+    stop_event.set()  # Break here - breakpoint on this line
+
+    t.join()
+    print("TEST SUCEEDED!")  # end

src/debugpy/_vendored/pydevd/tests_python/test_debugger_json.py

@@ -390,12 +390,16 @@ def _by_type(self, *msgs):
             ret[msg.__class__] = msg
         return ret
 
-    def write_continue(self, wait_for_response=True, thread_id="*"):
-        continue_request = self.write_request(pydevd_schema.ContinueRequest(pydevd_schema.ContinueArguments(threadId=thread_id)))
+    def write_continue(self, wait_for_response=True, thread_id="*", single_thread=False):
+        arguments = pydevd_schema.ContinueArguments(threadId=thread_id)
+        if single_thread:
+            arguments.singleThread = True
+        continue_request = self.write_request(pydevd_schema.ContinueRequest(arguments))
 
         if wait_for_response:
-            if thread_id != "*":
-                # event, response may be sent in any order
+            if single_thread:
+                # When singleThread=True, only the specified thread resumes.
+                # ContinuedEvent and ContinueResponse may arrive in any order.
                 msg1 = self.wait_for_json_message((ContinuedEvent, ContinueResponse))
                 msg2 = self.wait_for_json_message((ContinuedEvent, ContinueResponse))
                 by_type = self._by_type(msg1, msg2)
@@ -406,8 +410,10 @@ def write_continue(self, wait_for_response=True, thread_id="*"):
                 assert continued_ev.body.allThreadsContinued == False
                 assert continue_response.body.allThreadsContinued == False
             else:
-                # The continued event is received before the response.
-                self.wait_for_continued_event(all_threads_continued=True)
+                # Default: all threads resume regardless of the threadId sent.
+                # Per the DAP spec, singleThread must be explicitly True to
+                # resume only one thread. Wait for the continue response with
+                # allThreadsContinued=True.
                 continue_response = self.wait_for_response(continue_request)
                 assert continue_response.body.allThreadsContinued
 
@@ -800,6 +806,9 @@ def test_case_json_suspend_notification(case_setup_dap):
         json_facade.write_make_initial_run()
 
         json_hit = json_facade.wait_for_thread_stopped(line=break1_line)
+        # Per the DAP spec, a ContinueRequest without singleThread=True must resume
+        # all threads even when a specific threadId is provided. Verify the response
+        # has allThreadsContinued=True (the correct behavior).
         json_facade.write_continue(thread_id=json_hit.thread_id)
 
         json_hit = json_facade.wait_for_thread_stopped(line=break1_line)
@@ -808,6 +817,33 @@ def test_case_json_suspend_notification(case_setup_dap):
         writer.finished_ok = True
 
 
+def test_case_json_continue_all_threads(case_setup_dap):
+    """Regression test: ContinueRequest with a specific threadId (no singleThread=True)
+    must resume ALL threads, not just the requested one. This tests the fix for the
+    in-process debug adapter scenario where the adapter does not transform threadId to '*'.
+    """
+    with case_setup_dap.test_file("_debugger_case_multi_threads_continue.py") as writer:
+        json_facade = JsonFacade(writer)
+        # Simulate the in-process adapter: disable single notification mode.
+        # In this mode the server receives a specific threadId (not '*') directly
+        # from the client without the adapter transforming it.
+        json_facade.writer.write_multi_threads_single_notification(False)
+        break_line = writer.get_line_index_with_content("Break here")
+        json_facade.write_launch()
+        json_facade.write_set_breakpoints(break_line)
+        json_facade.write_make_initial_run()
+
+        # Wait for the breakpoint to be hit.
+        json_hit = json_facade.wait_for_thread_stopped(line=break_line)
+
+        # Send ContinueRequest with the specific thread's id (no singleThread=True).
+        # Per the DAP spec this must resume ALL threads, not just the specified one.
+        # The response must have allThreadsContinued=True.
+        json_facade.write_continue(thread_id=json_hit.thread_id)
+
+        writer.finished_ok = True
+
+
 def test_case_handled_exception_no_break_on_generator(case_setup_dap):
     with case_setup_dap.test_file("_debugger_case_ignore_exceptions.py") as writer:
         json_facade = JsonFacade(writer)