make ItemCache file ops threadsafe

Author: ThomasWaldmann

src/borg/fuse.py

@@ -120,6 +120,7 @@ def __init__(self, decrypted_repository):
         self.indirect_items = 0
         # Count of direct items, i.e. data is in self.fd
         self.direct_items = 0
+        self.lock = threading.Lock()
 
     def get(self, inode):
         offset = inode - self.offset
@@ -140,8 +141,9 @@ def get(self, inode):
             return Item(internal_dict=next(unpacker))
         elif self.meta[offset] == ord(b'S'):
             fd_offset = int.from_bytes(self.meta[offset + 1:offset + 9], 'little')
-            self.fd.seek(fd_offset, io.SEEK_SET)
-            return Item(internal_dict=next(msgpack.Unpacker(self.fd, read_size=1024)))
+            with self.lock:
+                self.fd.seek(fd_offset, io.SEEK_SET)
+                return Item(internal_dict=next(msgpack.Unpacker(self.fd, read_size=1024)))
         else:
             raise ValueError('Invalid entry type in self.meta')
 
@@ -218,8 +220,9 @@ def iter_archive_items(self, archive_item_ids, filter=None, consider_part_files=
                 #      ^------ offset ----------^
 
                 if current_spans_chunks:
-                    pos = self.fd.seek(0, io.SEEK_END)
-                    self.fd.write(current_item)
+                    with self.lock:
+                        pos = self.fd.seek(0, io.SEEK_END)
+                        self.fd.write(current_item)
                     self.meta[self.write_offset:self.write_offset + 9] = b'S' + pos.to_bytes(8, 'little')
                     self.direct_items += 1
                 else: