Removed caching from AnchorGenerator (#3745)

torchvision/models/detection/anchor_utils.py

 import torch
 from torch import nn, Tensor
 
-from typing import List, Optional, Dict
+from typing import List, Optional
 from .image_list import ImageList
 
 
@@ -28,7 +28,6 @@ class AnchorGenerator(nn.Module):
 
     __annotations__ = {
         "cell_anchors": Optional[List[torch.Tensor]],
-        "_cache": Dict[str, List[torch.Tensor]]
     }
 
     def __init__(
@@ -49,7 +48,6 @@ class AnchorGenerator(nn.Module):
         self.sizes = sizes
         self.aspect_ratios = aspect_ratios
         self.cell_anchors = None
-        self._cache = {}
 
     # TODO: https://github.com/pytorch/pytorch/issues/26792
     # For every (aspect_ratios, scales) combination, output a zero-centered anchor with those values.
@@ -131,14 +129,6 @@ class AnchorGenerator(nn.Module):
 
         return anchors
 
-    def cached_grid_anchors(self, grid_sizes: List[List[int]], strides: List[List[Tensor]]) -> List[Tensor]:
-        key = str(grid_sizes) + str(strides)
-        if key in self._cache:
-            return self._cache[key]
-        anchors = self.grid_anchors(grid_sizes, strides)
-        self._cache[key] = anchors
-        return anchors
-
     def forward(self, image_list: ImageList, feature_maps: List[Tensor]) -> List[Tensor]:
         grid_sizes = list([feature_map.shape[-2:] for feature_map in feature_maps])
         image_size = image_list.tensors.shape[-2:]
@@ -146,12 +136,10 @@ class AnchorGenerator(nn.Module):
         strides = [[torch.tensor(image_size[0] // g[0], dtype=torch.int64, device=device),
                     torch.tensor(image_size[1] // g[1], dtype=torch.int64, device=device)] for g in grid_sizes]
         self.set_cell_anchors(dtype, device)
-        anchors_over_all_feature_maps = self.cached_grid_anchors(grid_sizes, strides)
+        anchors_over_all_feature_maps = self.grid_anchors(grid_sizes, strides)
         anchors: List[List[torch.Tensor]] = []
         for i in range(len(image_list.image_sizes)):
             anchors_in_image = [anchors_per_feature_map for anchors_per_feature_map in anchors_over_all_feature_maps]
             anchors.append(anchors_in_image)
         anchors = [torch.cat(anchors_per_image) for anchors_per_image in anchors]
-        # Clear the cache in case that memory leaks.
-        self._cache.clear()
         return anchors