add test

tests/python/unittest/test_operator.py

@@ -5198,6 +5198,49 @@ def create_operator(self, ctx, shapes, dtypes):
         x = mx.nd.Custom(length=10, depth=10, op_type="no_input_op")
     assert_almost_equal(x.asnumpy(), np.ones(shape=(10, 10), dtype=np.float32))
 
+    # test custom operator fork
+    # see https://github.com/apache/incubator-mxnet/issues/14396
+    class AdditionOP(mx.operator.CustomOp):
+        def __init__(self):
+            super(AdditionOP, self).__init__()
+        def forward(self, is_train, req, in_data, out_data, aux):
+            out_data[0][:] = in_data[0] + in_data[1]
+        def backward(self, req, out_grad, in_data, out_data, in_grad, aux):
+            in_grad[0][:] = out_grad[0]
+            in_grad[1][:] = out_grad[0]
+
+    @mx.operator.register("AdditionOP")
+    class AdditionOPProp(mx.operator.CustomOpProp):
+        def __init__(self):
+            super(AdditionOPProp, self).__init__()
+        def list_arguments(self):
+            return ['a', 'b']
+        def list_outputs(self):
+            return ['output']
+        def infer_shape(self, in_shape):
+            return in_shape, [in_shape[0]]
+        def create_operator(self, ctx, shapes, dtypes):
+            return AdditionOP()
+
+    def custom_add():
+        a = mx.nd.array([1, 2, 3])
+        b = mx.nd.array([4, 5, 6])
+        a.attach_grad()
+        b.attach_grad()
+
+        with mx.autograd.record():
+            c = mx.nd.Custom(a, b, op_type='AdditionOP')
+
+        dc = mx.nd.array([7, 8, 9])
+        c.backward(dc)
+
+    custom_add()
+    from multiprocessing import Process
+    p = Process(target=custom_add)
+    p.start()
+    p.join(5)
+    assert not p.is_alive(), "deadlock may exist in custom operator"
+
 @with_seed()
 def test_psroipooling():
     for num_rois in [1, 2]: