[BUGFIX] WAR the dataloader issue with forked processes holding stale references

python/mxnet/gluon/data/dataloader.py

@@ -650,6 +650,10 @@ def __init__(self, dataset, batch_size=None, shuffle=False, sampler=None,
                 pin_device_id=self._pin_device_id,
                 prefetch=self._prefetch, **mx_iter_args)
         else:
+            nd.waitall()
+            import gc
+            gc.collect()
+            nd.waitall()
             if self._num_workers > 0:
                 if self._thread_pool:
                     self._worker_pool = ThreadPool(self._num_workers,