pickler override for np ndarrays

python/mxnet/gluon/data/dataloader.py

@@ -74,6 +74,38 @@ def reduce_ndarray(data):
 
 ForkingPickler.register(nd.NDArray, reduce_ndarray)
 
+if sys.platform == 'darwin' or sys.platform == 'win32':
+    def rebuild_np_ndarray(*args):
+        """Rebuild ndarray from pickled shared memory"""
+        # pylint: disable=no-value-for-parameter
+        return _mx_np.ndarray(nd.ndarray._new_from_shared_mem(*args))
+
+    def reduce_np_ndarray(data):
+        """Reduce ndarray to shared memory handle"""
+        return rebuild_np_ndarray, data._to_shared_mem()
+else:
+    def rebuild_np_ndarray(pid, fd, shape, dtype):
+        """Rebuild ndarray from pickled shared memory"""
+        # pylint: disable=no-value-for-parameter
+        if sys.version_info[0] == 2:
+            fd = multiprocessing.reduction.rebuild_handle(fd)
+        else:
+            fd = fd.detach()
+        return _mx_np.ndarray(nd.ndarray._new_from_shared_mem(pid, fd, shape, dtype))
+
+    def reduce_np_ndarray(data):
+        """Reduce ndarray to shared memory handle"""
+        # keep a local ref before duplicating fd
+        data = data.as_in_context(context.Context('cpu_shared', 0))
+        pid, fd, shape, dtype = data._to_shared_mem()
+        if sys.version_info[0] == 2:
+            fd = multiprocessing.reduction.reduce_handle(fd)
+        else:
+            fd = multiprocessing.reduction.DupFd(fd)
+        return rebuild_np_ndarray, (pid, fd, shape, dtype)
+
+ForkingPickler.register(_mx_np.ndarray, reduce_np_ndarray)
+
 
 class ConnectionWrapper(object):
     """Connection wrapper for multiprocessing that supports sending

tests/python/unittest/test_numpy_ndarray.py

@@ -1098,6 +1098,18 @@ def test_np_get_dtype():
             assert type(mx_arr.dtype) == type(np_arr.dtype)
 
 
+@use_np
+def test_np_ndarray_pickle():
+    a = np.random.uniform(size=(4, 5))
+    a_copy = a.copy()
+    import pickle
+    with open("np_ndarray_pickle_test_file", 'wb') as f:
+        pickle.dump(a_copy, f)
+    with open("np_ndarray_pickle_test_file", 'rb') as f:
+        a_load = pickle.load(f)
+    same(a.asnumpy(), a_load.asnumpy())
+
+
 if __name__ == '__main__':
     import nose
     nose.runmodule()