Keep block caches usable after pickling

Author: fallenmi

docs/source/changelog.rst

@@ -1,6 +1,14 @@
 Changelog
 =========
 
+Dev
+---
+
+Fixes
+
+- Avoid mutating live ``BlockCache`` and ``BackgroundBlockCache`` instances
+  when pickling (#2102)
+
 2026.7.0
 --------
 

fsspec/caching.py

@@ -375,7 +375,7 @@ def cache_info(self):
         return self._fetch_block_cached.cache_info()
 
     def __getstate__(self) -> dict[str, Any]:
-        state = self.__dict__
+        state = self.__dict__.copy()
         del state["_fetch_block_cached"]
         return state
 
@@ -832,7 +832,7 @@ def close(self) -> None:
         del self._fetch_block_cached
 
     def __getstate__(self) -> dict[str, Any]:
-        state = self.__dict__
+        state = self.__dict__.copy()
         del state["_fetch_block_cached"]
         del state["_thread_executor"]
         del state["_fetch_future_block_number"]

fsspec/tests/test_caches.py

@@ -194,7 +194,9 @@ def test_cache_pickleable(Cache_imp):
     size = 100
     cache = Cache_imp(blocksize, _fetcher, size)
     cache._fetch(0, 5)  # fill in cache
-    unpickled = pickle.loads(pickle.dumps(cache))
+    payload = pickle.dumps(cache)
+    assert cache._fetch(0, 10) == b"0" * 10
+    unpickled = pickle.loads(payload)
     assert isinstance(unpickled, Cache_imp)
     assert unpickled.blocksize == blocksize
     assert unpickled.size == size