[User-streams] Make torch.Event weakref compatible (#164522)

Pull Request resolved: https://github.com/pytorch/pytorch/pull/164522
Approved by: https://github.com/williamwen42
ghstack dependencies: #164304

test/dynamo/test_compile.py

@@ -234,27 +234,6 @@ class InPlaceCompilationTests(TestCase):
         with self.assertRaises(IndexError):
             fn(torch.randn(10), 99)
 
-    def test_list_bad_weakref(self):
-        import weakref
-
-        a = torch.Event()
-        with self.assertRaises(TypeError):
-            weakref.ref(a)
-
-        @torch.compile(backend="eager")
-        class Mod(torch.nn.Module):
-            def __init__(self, event):
-                super().__init__()
-                self.event = event
-
-            def forward(self, x):
-                return x * int(self.event.query())
-
-        e = torch.Event()
-        m = Mod(e)
-        a = torch.randn(10)
-        self.assertEqual(m(a), a)
-
 
 # The private variants of the below functions are extensively tested
 # So as long as the signatures match we're good

test/dynamo/test_streams.py

@@ -21,6 +21,11 @@ class TestStreams(torch._dynamo.test_case.TestCase):
         s = torch.Stream()
         weakref.ref(s)
 
+    @requires_cuda
+    def test_event_weakref(self):
+        e = torch.Event()
+        weakref.ref(e)
+
     @requires_cuda
     def test_run_opcheck(self):
         from torch._dynamo.variables.streams import fork_stream, join_stream

torch/csrc/Event.cpp

@@ -49,6 +49,7 @@ static PyObject* THPEvent_pynew(
   }
 
   THPEvent* self = reinterpret_cast<THPEvent*>(ptr.get());
+  self->weakreflist = nullptr;
 
   // TODO: blocking and interprocess are not supported yet. To support them, the
   // flag system of c10::Event needs to be refactored. C10::Event should also
@@ -73,6 +74,7 @@ PyObject* THPEvent_new(c10::DeviceType device_type, c10::EventFlag flag) {
   auto self = THPObjectPtr{type->tp_alloc(type, 0)};
   TORCH_CHECK(self, "Failed to allocate memory for Event");
   auto self_ = reinterpret_cast<THPEvent*>(self.get());
+  self_->weakreflist = nullptr;
   new (&self_->event) c10::Event(device_type, flag);
   return self.release();
 }
@@ -82,6 +84,7 @@ static void THPEvent_dealloc(THPEvent* self) {
     pybind11::gil_scoped_release no_gil{};
     self->event.~Event();
   }
+  PyObject_ClearWeakRefs((PyObject*)self);
   Py_TYPE(self)->tp_free(reinterpret_cast<PyObject*>(self));
 }
 
@@ -282,7 +285,8 @@ static PyMethodDef THPEvent_methods[] = {
     {"synchronize", THPEvent_synchronize, METH_NOARGS, nullptr},
     {"ipc_handle", THPEvent_ipc_handle, METH_NOARGS, nullptr},
     {nullptr}};
-
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Winvalid-offsetof"
 PyTypeObject THPEventType = {
     PyVarObject_HEAD_INIT(nullptr, 0)
     "torch.Event", /* tp_name */
@@ -308,7 +312,7 @@ PyTypeObject THPEventType = {
     nullptr, /* tp_traverse */
     nullptr, /* tp_clear */
     nullptr, /* tp_richcompare */
-    0, /* tp_weaklistoffset */
+    offsetof(THPEvent, weakreflist), /* tp_weaklistoffset */
     nullptr, /* tp_iter */
     nullptr, /* tp_iternext */
     THPEvent_methods, /* tp_methods */
@@ -323,6 +327,7 @@ PyTypeObject THPEventType = {
     nullptr, /* tp_alloc */
     THPEvent_pynew, /* tp_new */
 };
+#pragma GCC diagnostic pop
 
 void THPEvent_init(PyObject* module) {
   THPEventClass = &THPEventType;

torch/csrc/Event.h

@@ -7,6 +7,7 @@
 struct TORCH_API THPEvent {
   PyObject_HEAD
   c10::Event event;
+  PyObject* weakreflist;
 };
 TORCH_API extern PyTypeObject* THPEventClass;
 TORCH_API extern PyTypeObject THPEventType;