From bb71fa8ef1de643f8ab8ace07384b7ec4280370a Mon Sep 17 00:00:00 2001
From: vmoens <vincentmoens@gmail.com>
Date: Sat, 9 Dec 2023 06:47:34 +0000
Subject: [PATCH] amend

---
 tensordict/_td.py | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/tensordict/_td.py b/tensordict/_td.py
index 93209fc2d..40d56f3c4 100644
--- a/tensordict/_td.py
+++ b/tensordict/_td.py
@@ -1477,7 +1477,7 @@ def memmap_(
         self,
         prefix: str | None = None,
         copy_existing: bool = False,
-        num_threads: int=0,
+        num_threads: int = 0,
         executor=None,
         futures=None,
     ) -> T:
@@ -1488,7 +1488,12 @@ def memmap_(
 
             with ThreadPoolExecutor(max_workers=num_threads) as executor:
                 futures = []
-                result = self.memmap_(prefix=prefix, copy_existing=copy_existing, executor=executor, futures=futures)
+                result = self.memmap_(
+                    prefix=prefix,
+                    copy_existing=copy_existing,
+                    executor=executor,
+                    futures=futures,
+                )
                 for future in futures:
                     future.result()
                 return result
@@ -1525,22 +1530,28 @@ def save_metadata(data: TensorDictBase, filepath, metadata=None):
                     # ensure subdirectory exists
                     os.makedirs(prefix / key, exist_ok=True)
                     self._tensordict[key] = value.memmap_(
-                        prefix=prefix / key, copy_existing=copy_existing, executor=executor, futures=futures,
+                        prefix=prefix / key,
+                        copy_existing=copy_existing,
+                        executor=executor,
+                        futures=futures,
                     )
                 else:
-                    self._tensordict[key] = value.memmap_(executor=executor, futures=futures)
+                    self._tensordict[key] = value.memmap_(
+                        executor=executor, futures=futures
+                    )
                 continue
             else:
                 # user did specify location and memmap is in wrong place, so we copy
-                def _populate():
+                def _populate(value=value, key=key, copy_existing=copy_existing):
+                    filename = None if prefix is None else str(prefix / f"{key}.memmap")
                     self._tensordict[key] = MemoryMappedTensor.from_tensor(
                         value,
-                        filename=str(prefix / f"{key}.memmap")
-                        if prefix is not None
-                        else None,
+                        filename=filename,
                         copy_existing=copy_existing,
+                        existsok=True,
                         # copy_existing=copy_existing,
                     )
+
                 if executor is None:
                     _populate()
                 else:
@@ -1560,7 +1571,9 @@ def _populate():
                     metadata=metadata,
                 )
             else:
-                futures.append(executor.submit(save_metadata, args=(self, prefix / "meta.json", metadata)))
+                futures.append(
+                    executor.submit(save_metadata, self, prefix / "meta.json", metadata)
+                )
         self._is_memmap = True
         self._is_shared = False  # since they are mutually exclusive
         self._device = torch.device("cpu")