HF_HUB_KEEP_LOCK_FILES to prevent rare concurrency issue

The lock file could be removed when the 2nd process gets the lock.
And then the 3rd process will lock on a different lock file handle.
Although the lock path stays the same.

1st proc gets the lock
2nd proc waits for the lock
1st proc releases the lock
1st proc removes the lock file
2nd proc gets the lock
3rd proc creates a new lock file and gets the lock

Add ENV 'HF_HUB_KEEP_LOCK_FILES' to give user option to keep the lock
files to prevent concurrency issues.

docs/source/en/package_reference/environment_variables.md

@@ -74,6 +74,12 @@ small files will be duplicated to ease user experience while bigger files are sy
 
 For more details, see the [download guide](../guides/download#download-files-to-local-folder).
 
+### HF_HUB_KEEP_LOCK_FILES
+
+Lock files are used to ensure the downloading in parallel won't overwrite. By default, the lock file will be deleted
+automatically. However, the deletion would cause concurrency issues in rare cases. Set this to `True` to prevent this
+kind of concurrency issue.
+
 ## Boolean values
 
 The following environment variables expect a boolean value. The variable will be considered

src/huggingface_hub/constants.py

@@ -130,6 +130,11 @@ def _as_int(value: Optional[str]) -> Optional[int]:
     _as_int(os.environ.get("HF_HUB_LOCAL_DIR_AUTO_SYMLINK_THRESHOLD")) or 5 * 1024 * 1024
 )
 
+# Lock files are used to ensure the downloading in parallel won't overwrite. By default, the lock file will be deleted
+# automatically. However, the deletion would cause concurrency issues in rare cases. Set this to TRUE to prevent this
+# kind of concurrency issue.
+HF_HUB_KEEP_LOCK_FILES: bool = _is_true(os.environ.get("HF_HUB_KEEP_LOCK_FILES"))
+
 # List frameworks that are handled by the InferenceAPI service. Useful to scan endpoints and check which models are
 # deployed and running. Since 95% of the models are using the top 4 frameworks listed below, we scan only those by
 # default. We still keep the full list of supported frameworks in case we want to scan all of them.

src/huggingface_hub/file_download.py

@@ -29,6 +29,7 @@
     ENDPOINT,
     HF_HUB_DISABLE_SYMLINKS_WARNING,
     HF_HUB_ENABLE_HF_TRANSFER,
+    HF_HUB_KEEP_LOCK_FILES,
     HUGGINGFACE_CO_URL_TEMPLATE,
     HUGGINGFACE_HEADER_X_LINKED_ETAG,
     HUGGINGFACE_HEADER_X_LINKED_SIZE,
@@ -1475,10 +1476,11 @@ def _resumable_file_manager() -> Generator[io.BufferedWriter, None, None]:
                 _chmod_and_replace(temp_file.name, local_dir_filepath)
             pointer_path = local_dir_filepath  # for return value
 
-    try:
-        os.remove(lock_path)
-    except OSError:
-        pass
+    if not HF_HUB_KEEP_LOCK_FILES:
+        try:
+            os.remove(lock_path)
+        except OSError:
+            pass
 
     return pointer_path