[BugFix] Read-only compatibility in MemoryMappedTensor

tensordict/memmap.py

@@ -9,6 +9,7 @@
 
 import mmap
 import os
+import stat
 
 import sys
 import tempfile
@@ -266,7 +267,7 @@ def from_tensor(
                 result = result.view(shape)
             result = cls(result)
         result._handler = handler
-        result._filename = filename
+        result.filename = filename
         result.index = None
         result.parent_shape = shape
         if copy_data:
@@ -321,7 +322,7 @@ def from_storage(
 
         tensor = cls(tensor)
         if filename is not None:
-            tensor._filename = filename
+            tensor.filename = filename
         elif handler is not None:
             tensor._handler = handler
         if index is not None:
@@ -339,6 +340,17 @@ def filename(self):
             raise RuntimeError("The MemoryMappedTensor has no file associated.")
         return filename
 
+    @filename.setter
+    def filename(self, value):
+        if value is None and self._filename is None:
+            return
+        value = str(Path(value).absolute())
+        if self._filename is not None and value != self._filename:
+            raise RuntimeError(
+                "the MemoryMappedTensor has already a filename associated."
+            )
+        self._filename = value
+
     @classmethod
     def empty_like(cls, input, *, filename=None):
         # noqa: D417
@@ -596,7 +608,7 @@ def empty(cls, *args, **kwargs):
                     *offsets_strides,
                 )
                 result = cls(result)
-                result._filename = filename
+                result.filename = filename
                 return result
             return result
 
@@ -712,6 +724,8 @@ def from_filename(cls, filename, dtype, shape, index=None):
                 tensor.
 
         """
+        writable = _is_writable(filename)
+
         if isinstance(shape, torch.Tensor):
             func_offset_stride = getattr(
                 torch, "_nested_compute_contiguous_strides_offsets", None
@@ -724,24 +738,40 @@ def from_filename(cls, filename, dtype, shape, index=None):
                     "nested tensors. Please upgrade to a more recent "
                     "version."
                 )
-            tensor = torch.from_file(
-                str(filename), shared=True, dtype=dtype, size=shape.prod(-1).sum().int()
-            )
+            if writable:
+                tensor = torch.from_file(
+                    str(filename),
+                    shared=True,
+                    dtype=dtype,
+                    size=shape.prod(-1).sum().int(),
+                )
+            else:
+                with open(str(filename), "rb") as f:
+                    mm = mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ)
+                    tensor = torch.frombuffer(mm, dtype=dtype)
+                    # mm.close()
             tensor = torch._nested_view_from_buffer(
                 tensor,
                 shape,
                 *offsets_strides,
             )
         else:
             shape = torch.Size(shape)
-            tensor = torch.from_file(
-                str(filename), shared=True, dtype=dtype, size=shape.numel()
-            ).view(shape)
+            # whether the file already existed
+            if writable:
+                tensor = torch.from_file(
+                    str(filename), shared=True, dtype=dtype, size=shape.numel()
+                )
+            else:
+                with open(str(filename), "rb") as f:
+                    mm = mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ)
+                    tensor = torch.frombuffer(mm, dtype=dtype)
+            tensor = tensor.view(shape)
 
         if index is not None:
             tensor = tensor[index]
         out = cls(tensor)
-        out._filename = filename
+        out.filename = filename
         out._handler = None
         out.index = index
         out.parent_shape = shape
@@ -787,7 +817,7 @@ def from_handler(cls, handler, dtype, shape, index=None):
         if index is not None:
             out = out[index]
         out = cls(out)
-        out._filename = None
+        out.filename = None
         out._handler = handler
         out.index = index
         out.parent_shape = shape
@@ -880,7 +910,7 @@ def _index_wrap(self, tensor, item, check=False):
             return tensor
         tensor = MemoryMappedTensor(tensor)
         tensor._handler = getattr(self, "_handler", None)
-        tensor._filename = getattr(self, "_filename", None)
+        tensor.filename = getattr(self, "_filename", None)
         tensor.index = item
         tensor.parent_shape = getattr(self, "parent_shape", None)
         return tensor
@@ -1038,3 +1068,12 @@ def _unbind(tensor, dim):
 @implements_for_memmap(torch.chunk)
 def _chunk(input, chunks, dim=0):
     return input.chunk(chunks, dim=dim)
+
+
+def _is_writable(file_path):
+    file_path = str(file_path)
+    if os.path.exists(file_path):
+        st = os.stat(file_path)
+        return bool(st.st_mode & (stat.S_IWUSR | stat.S_IWGRP | stat.S_IWOTH))
+    # Assume that the file can be written in the directory
+    return True

test/test_memmap.py

@@ -4,6 +4,8 @@
 # LICENSE file in the root directory of this source tree.
 import argparse
 import gc
+import os
+import stat
 from contextlib import nullcontext
 from pathlib import Path
 
@@ -12,7 +14,7 @@
 from _utils_internal import get_available_devices
 from tensordict import TensorDict
 
-from tensordict.memmap import MemoryMappedTensor
+from tensordict.memmap import _is_writable, MemoryMappedTensor
 from torch import multiprocessing as mp
 
 TIMEOUT = 100
@@ -157,7 +159,7 @@ def test_zeros(self, shape, dtype, device, tmp_path, from_path, shape_arg):
         if dtype is not None:
             assert t.dtype is dtype
         if filename is not None:
-            assert t.filename == filename
+            assert t.filename == str(Path(filename).absolute())
         assert (t == 0).all()
 
     @pytest.mark.parametrize("shape_arg", ["expand", "arg", "kwarg"])
@@ -191,7 +193,7 @@ def test_ones(self, shape, dtype, device, tmp_path, from_path, shape_arg):
         if dtype is not None:
             assert t.dtype is dtype
         if filename is not None:
-            assert t.filename == filename
+            assert t.filename == str(Path(filename).absolute())
         assert (t == 1).all()
 
     @pytest.mark.parametrize("shape_arg", ["expand", "arg", "kwarg"])
@@ -225,7 +227,7 @@ def test_empty(self, shape, dtype, device, tmp_path, from_path, shape_arg):
         if dtype is not None:
             assert t.dtype is dtype
         if filename is not None:
-            assert t.filename == filename
+            assert t.filename == str(Path(filename).absolute())
 
     @pytest.mark.parametrize("shape_arg", ["expand", "arg", "kwarg"])
     def test_full(self, shape, dtype, device, tmp_path, from_path, shape_arg):
@@ -258,7 +260,7 @@ def test_full(self, shape, dtype, device, tmp_path, from_path, shape_arg):
         if dtype is not None:
             assert t.dtype is dtype
         if filename is not None:
-            assert t.filename == filename
+            assert t.filename == str(Path(filename).absolute())
         assert (t == 2).all()
 
     def test_zeros_like(self, shape, dtype, device, tmp_path, from_path):
@@ -272,7 +274,7 @@ def test_zeros_like(self, shape, dtype, device, tmp_path, from_path):
         if dtype is not None:
             assert t.dtype is dtype
         if filename is not None:
-            assert t.filename == filename
+            assert t.filename == str(Path(filename).absolute())
         assert (t == 0).all()
 
     def test_ones_like(self, shape, dtype, device, tmp_path, from_path):
@@ -286,7 +288,7 @@ def test_ones_like(self, shape, dtype, device, tmp_path, from_path):
         if dtype is not None:
             assert t.dtype is dtype
         if filename is not None:
-            assert t.filename == filename
+            assert t.filename == str(Path(filename).absolute())
         assert (t == 1).all()
 
     def test_full_like(self, shape, dtype, device, tmp_path, from_path):
@@ -300,7 +302,7 @@ def test_full_like(self, shape, dtype, device, tmp_path, from_path):
         if dtype is not None:
             assert t.dtype is dtype
         if filename is not None:
-            assert t.filename == filename
+            assert t.filename == str(Path(filename).absolute())
         assert (t == 2).all()
 
     def test_from_filename(self, shape, dtype, device, tmp_path, from_path):
@@ -715,6 +717,80 @@ def test_save_td_with_nested(self, tmpdir):
                 assert (td[i, j] == tdsave[i, j]).all()
 
 
+class TestReadWrite:
+    def test_read_only(self, tmpdir):
+        tmpdir = Path(tmpdir)
+        file_path = tmpdir / "elt.mmap"
+        mmap = MemoryMappedTensor.from_filename(
+            filename=file_path, shape=[2, 3], dtype=torch.float64
+        )
+        mmap.copy_(torch.arange(6).view(2, 3))
+
+        file_path = str(file_path.absolute())
+
+        assert _is_writable(file_path)
+        # Modify the permissions field to set the desired permissions
+        new_permissions = stat.S_IREAD  # | stat.S_IWRITE | stat.S_IEXEC
+
+        # change permission
+        os.chmod(file_path, new_permissions)
+
+        # Get the current file status
+        assert not _is_writable(file_path)
+
+        del mmap
+
+        # load file
+        mmap = MemoryMappedTensor.from_filename(
+            filename=file_path, shape=[2, 3], dtype=torch.float64
+        )
+        assert (mmap.reshape(-1) == torch.arange(6)).all()
+
+    @pytest.mark.skipif(not HAS_NESTED_TENSOR, reason="Nested tensor incomplete")
+    def test_read_only_nested(self, tmpdir):
+        tmpdir = Path(tmpdir)
+        file_path = tmpdir / "elt.mmap"
+        data = MemoryMappedTensor.from_tensor(torch.arange(26), filename=file_path)
+        mmap = MemoryMappedTensor.from_storage(
+            data.untyped_storage(),
+            filename=file_path,
+            shape=torch.tensor([[2, 3], [4, 5]]),
+            dtype=data.dtype,
+        )
+
+        file_path = str(file_path.absolute())
+        assert _is_writable(file_path)
+
+        # Modify the permissions field to set the desired permissions
+        new_permissions = stat.S_IREAD  # | stat.S_IWRITE | stat.S_IEXEC
+
+        # change permission
+        os.chmod(file_path, new_permissions)
+
+        # Get the current file status
+        assert not _is_writable(file_path)
+
+        # load file
+        mmap1 = MemoryMappedTensor.from_filename(
+            filename=file_path, shape=torch.tensor([[2, 3], [4, 5]]), dtype=data.dtype
+        )
+        assert (mmap1[0].view(-1) == torch.arange(6)).all()
+        assert (mmap1[1].view(-1) == torch.arange(6, 26)).all()
+        # test filename
+        assert mmap1.filename == mmap.filename
+        assert mmap1.filename == data.filename
+        assert mmap1.filename == data.untyped_storage().filename
+        with pytest.raises(AssertionError):
+            assert mmap1.untyped_storage().filename == data.untyped_storage().filename
+
+        os.chmod(str(file_path), 0o444)
+        data.fill_(0)
+        os.chmod(str(file_path), 0o444)
+
+        assert (mmap1[0].view(-1) == 0).all()
+        assert (mmap1[1].view(-1) == 0).all()
+
+
 if __name__ == "__main__":
     args, unknown = argparse.ArgumentParser().parse_known_args()
     pytest.main([__file__, "--capture", "no", "--exitfirst"] + unknown)