Always wait for threads in subinterpreters.

ericsnowcurrently · Oct 2, 2023 · Sep 25, 2023 · Sep 26, 2023 · Sep 26, 2023 · Sep 26, 2023
commit 4e88c2b6d1b953b9ee9ea7fc21e1ed192b973df5
diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
@@ -26,6 +26,11 @@
 from test import lock_tests
 from test import support
 
+try:
+    from test.support import interpreters
+except ModuleNotFoundError:
+    interpreters = None
+
 threading_helper.requires_working_threading(module=True)
 
 # Between fork() and exec(), only async-safe functions are allowed (issues
@@ -35,6 +40,12 @@
 platforms_to_skip = ('netbsd5', 'hp-ux11')
 
 
+def requires_subinterpreters(meth):
+    """Decorator to skip a test if subinterpreters are not supported."""
+    return unittest.skipIf(interpreters is None,
+                           'subinterpreters required')(meth)
+
+
 def restore_default_excepthook(testcase):
     testcase.addCleanup(setattr, threading, 'excepthook', threading.excepthook)
     threading.excepthook = threading.__excepthook__
@@ -1298,6 +1309,45 @@ def f():
         # The thread was joined properly.
         self.assertEqual(os.read(r, 1), b"x")
 
+    @requires_subinterpreters
+    def test_threads_join_with_no_main(self):
+#        r_thread, w_thread = self.pipe()
+        r_interp, w_interp = self.pipe()
+
+        INTERP = b'I'
+        FINI = b'F'
+        DONE = b'D'
+
+        interp = interpreters.create()
+        interp.run(f"""if True:
+            import os
+            import threading
+            import time
+
+            done = False
+
+            def notify_fini():
+                global done
+                done = True
+                os.write({w_interp}, {FINI!r})
+                t.join()
+            threading._register_atexit(notify_fini)
+
+            def task():
+                while not done:
+                    time.sleep(0.1)
+                os.write({w_interp}, {DONE!r})
+            t = threading.Thread(target=task)
+            t.start()
+
+            os.write({w_interp}, {INTERP!r})
+            """)
+        interp.close()
+
+        self.assertEqual(os.read(r_inerp, 1), INTERP)
+        self.assertEqual(os.read(r_inerp, 1), FINI)
+        self.assertEqual(os.read(r_inerp, 1), DONE)
+
     @cpython_only
     def test_daemon_threads_fatal_error(self):
         subinterp_code = f"""if 1:

diff --git a/Lib/threading.py b/Lib/threading.py
@@ -38,6 +38,7 @@
 _allocate_lock = _thread.allocate_lock
 _set_sentinel = _thread._set_sentinel
 get_ident = _thread.get_ident
+_is_main_interpreter = _thread._is_main_interpreter
 try:
     get_native_id = _thread.get_native_id
     _HAVE_THREAD_NATIVE_ID = True
@@ -1567,7 +1568,7 @@ def _shutdown():
     # the main thread's tstate_lock - that won't happen until the interpreter
     # is nearly dead.  So we release it here.  Note that just calling _stop()
     # isn't enough:  other threads may already be waiting on _tstate_lock.
-    if _main_thread._is_stopped:
+    if _main_thread._is_stopped and _is_main_interpreter():
         # _shutdown() was already called
         return
 

diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
@@ -1590,6 +1590,18 @@ PyDoc_STRVAR(excepthook_doc,
 \n\
 Handle uncaught Thread.run() exception.");
 
+static PyObject *
+thread__is_main_interpreter(PyObject *module, PyObject *Py_UNUSED(ignored))
+{
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    return PyBool_FromLong(_Py_IsMainInterpreter(interp));
+}
+
+PyDoc_STRVAR(thread__is_main_interpreter_doc,
+"_is_main_interpreter()\n\
+\n\
+Return True if the current interpreter is the main Python interpreter.");
+
 static PyMethodDef thread_methods[] = {
     {"start_new_thread",        (PyCFunction)thread_PyThread_start_new_thread,
      METH_VARARGS, start_new_doc},
@@ -1619,8 +1631,10 @@ static PyMethodDef thread_methods[] = {
      METH_VARARGS, stack_size_doc},
     {"_set_sentinel",           thread__set_sentinel,
      METH_NOARGS, _set_sentinel_doc},
-    {"_excepthook",              thread_excepthook,
+    {"_excepthook",             thread_excepthook,
      METH_O, excepthook_doc},
+    {"_is_main_interpreter",    thread__is_main_interpreter,
+     METH_NOARGS, thread__is_main_interpreter_doc},
     {NULL,                      NULL}           /* sentinel */
 };