Fix multithreading stepping in 3.12 and later (#1798)

* Fix multithreaded stepping to not have 'return' events when a thread is already suspended

* Update after removing blank line

* Remove unnecessary change for start method

CONTRIBUTING.md

@@ -171,6 +171,10 @@ That will generate a log from the test run.
 
 Logging the test output can be tricky so here's some information on how to debug the tests.
 
+#### Running pydevd tests inside of VS code
+
+You can also run the pydevd tests inside of VS code using the test explorer (and debug the pytest code). To do so, set PYTHONPATH=. and open the `src/debugpy/_vendored/pydevd` folder in VS code. The test explorer should find all of the pydevd tests.
+
 #### How to add more logging
 
 The pydevd tests log everything to the console and to a text file during the test. If you scroll up in the console, it should show the log file it read the logs from:

src/debugpy/.vscode/settings.json

@@ -0,0 +1,7 @@
+{
+    "python.testing.pytestArgs": [
+        "."
+    ],
+    "python.testing.unittestEnabled": false,
+    "python.testing.pytestEnabled": true
+}

src/debugpy/_vendored/pydevd/_pydevd_sys_monitoring/_pydevd_sys_monitoring.py

@@ -1085,6 +1085,11 @@ def _return_event(code, instruction, retval):
             _plugin_stepping(py_db, step_cmd, "return", frame, thread_info)
         return
     
+    if info.pydev_state == STATE_SUSPEND:
+        # We're already suspended, don't handle any more events on this thread.
+        _do_wait_suspend(py_db, thread_info, frame, "return", None)
+        return
+    
     # Python line stepping
     stop_frame = info.pydev_step_stop
     if step_cmd in (CMD_STEP_INTO, CMD_STEP_INTO_MY_CODE, CMD_STEP_INTO_COROUTINE):

src/debugpy/_vendored/pydevd/_pydevd_sys_monitoring/_pydevd_sys_monitoring_cython.pyx

@@ -1091,6 +1091,11 @@ cdef _return_event(code, instruction, retval):
             _plugin_stepping(py_db, step_cmd, "return", frame, thread_info)
         return
     
+    if info.pydev_state == STATE_SUSPEND:
+        # We're already suspended, don't handle any more events on this thread.
+        _do_wait_suspend(py_db, thread_info, frame, "return", None)
+        return
+    
     # Python line stepping
     stop_frame = info.pydev_step_stop
     if step_cmd in (CMD_STEP_INTO, CMD_STEP_INTO_MY_CODE, CMD_STEP_INTO_COROUTINE):

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

@@ -5,12 +5,18 @@ or should keep waiting for the thread 2 to run if only thread 1 is resumed.
 """
 
 import threading
+import requests
+import time
 
 event0 = threading.Event()
 event1 = threading.Event()
 event2 = threading.Event()
 event3 = threading.Event()
 
+def request_get(url):
+    # return "abc"
+    with requests.get(url) as data:
+        return data.text
 
 def _thread1():
     _event1_set = False
@@ -19,6 +25,7 @@ def _thread1():
     while not event0.is_set():
         event0.wait(timeout=0.001)
 
+    time.sleep(.1)
     event1.set()  # Break thread 1
     _event1_set = True
 
@@ -33,6 +40,9 @@ def _thread2():
     event0.set()
 
     while not event1.is_set():
+        # Do something interesting that takes a while. This verifies we 
+        # only get stop events for the thread with a breakpoint.
+        print(len(request_get("https://dns.google//")))
         event1.wait(timeout=0.001)
 
     event2.set()

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

@@ -3359,6 +3359,9 @@ def test_step_next_step_in_multi_threads(case_setup_dap, stepping_resumes_all_th
         thread_name_to_id = dict((t["name"], t["id"]) for t in response.body.threads)
         assert json_hit.thread_id == thread_name_to_id["thread1"]
 
+        stopped_events = json_facade.mark_messages(StoppedEvent)
+        assert len(stopped_events) == 1
+
         timeout_at = time.time() + 30
         checks = 0
 

tests/debug/session.py

@@ -867,6 +867,8 @@ class Session(object):
             assert len(expected_frames) <= len(frames)
             assert expected_frames == frames[0 : len(expected_frames)]
 
+        assert len(frames) > 0
+
         fid = frames[0]("id", int)
         return StopInfo(stopped, frames, tid, fid)