Add optional file-based listings caching

Author: gutzbenj

ci/environment-win.yml

@@ -20,3 +20,5 @@ dependencies:
   - python-libarchive-c
   - numpy
   - nomkl
+  - diskcache
+  - appdirs

docs/source/api.rst

@@ -41,7 +41,8 @@ Base Classes
    fsspec.core.BaseCache
    fsspec.core.get_fs_token_paths
    fsspec.core.url_to_fs
-   fsspec.dircache.DirCache
+   fsspec.dircache.MemDirCache
+   fsspec.dircache.FileDirCache
    fsspec.registry.ReadOnlyRegistry
    fsspec.registry.register_implementation
    fsspec.callbacks.Callback
@@ -75,7 +76,10 @@ Base Classes
 
 .. autofunction:: fsspec.core.url_to_fs
 
-.. autoclass:: fsspec.dircache.DirCache
+.. autoclass:: fsspec.dircache.MemDirCache
+   :members: __init__
+
+.. autoclass:: fsspec.dircache.FileDirCache
    :members: __init__
 
 .. autoclass:: fsspec.registry.ReadOnlyRegistry

docs/source/changelog.rst

@@ -1,6 +1,14 @@
 Changelog
 =========
 
+Dev
+---------
+
+Enhancements
+
+- add filebased listing cache using diskcache
+
+
 2022.01.0
 ---------
 

docs/source/features.rst

@@ -179,15 +179,18 @@ Listings Caching
 ----------------
 
 For some implementations, getting file listings (i.e., ``ls`` and anything that
-depends on it) is expensive. These implementations use dict-like instances of
-:class:`fsspec.dircache.DirCache` to manage the listings.
-
-The cache allows for time-based expiry of entries with the ``listings_expiry_time``
-parameter, or LRU expiry with the ``max_paths`` parameter. These can be
-set on any implementation instance that uses listings caching; or to skip the
-caching altogether, use ``use_listings_cache=False``. That would be appropriate
-when the target location is known to be volatile because it is being written
-to from other sources.
+depends on it) is expensive. These implementations use either dict-like instances of
+:class:`fsspec.dircache.MemDirCache` or file-based caching with instances of
+:class:`fsspec.dircache.FileDirCache` to manage the listings.
+
+The type of cache that is used, can be controlled via the keyword ``listings_cache_type``
+that has to be one of `memdircache` or `filedircache`. The cache allows for time-based expiry
+of entries with the ``listings_expiry_time`` parameter, or LRU expiry with the ``max_paths``
+parameter. These can be set on any implementation instance that uses listings caching; or to
+skip the caching altogether, use ``use_listings_cache=False``. That would be appropriate
+when the target location is known to be volatile because it is being written to from other
+sources. If you want to use the file-based caching, you can also provide the argument
+``listings_cache_location`` to determine where the cache file is stored.
 
 When the ``fsspec`` instance writes to the backend, the method ``invalidate_cache``
 is called, so that subsequent listing of the given paths will force a refresh. In

fsspec/dircache.py

@@ -1,9 +1,13 @@
+import logging
 import time
 from collections.abc import MutableMapping
 from functools import lru_cache
+from pathlib import Path
 
+logger = logging.getLogger("fsspec")
 
-class DirCache(MutableMapping):
+
+class MemDirCache(MutableMapping):
     """
     Caching of directory listings, in a structure like::
 
@@ -91,6 +95,95 @@ def __iter__(self):
 
     def __reduce__(self):
         return (
-            DirCache,
+            MemDirCache,
             (self.use_listings_cache, self.listings_expiry_time, self.max_paths),
         )
+
+
+class FileDirCache(MutableMapping):
+    def __init__(
+        self,
+        use_listings_cache=True,
+        listings_expiry_time=None,
+        listings_cache_location=None,
+        **kwargs,
+    ):
+        """
+
+        Parameters
+        ----------
+        use_listings_cache: bool
+            If False, this cache never returns items, but always reports KeyError,
+            and setting items has no effect
+        listings_expiry_time: int or float (optional)
+            Time in seconds that a listing is considered valid. If None,
+            listings do not expire.
+        listings_cache_location: str (optional)
+            Directory path at which the listings cache file is stored. If None,
+            an autogenerated path at the user folder is created.
+
+        """
+        import appdirs
+        from diskcache import Cache
+
+        listings_expiry_time = listings_expiry_time and float(listings_expiry_time)
+
+        if listings_cache_location:
+            listings_cache_location = Path(listings_cache_location) / str(
+                listings_expiry_time
+            )
+            listings_cache_location.mkdir(exist_ok=True, parents=True)
+        else:
+            listings_cache_location = Path(
+                appdirs.user_cache_dir(appname="fsspec_dircache")
+            ) / str(listings_expiry_time)
+
+        try:
+            listings_cache_location.mkdir(exist_ok=True, parents=True)
+        except Exception:
+            logger.error(
+                f"folder for dircache could not be created at {listings_cache_location}"
+            )
+
+        self.cache_location = listings_cache_location
+
+        logger.info(f"Dircache located at {listings_cache_location}")
+
+        self._cache = Cache(directory=listings_cache_location)
+        self.use_listings_cache = use_listings_cache
+        self.listings_expiry_time = listings_expiry_time
+
+    def __getitem__(self, item):
+        """Draw item as fileobject from cache, retry if timeout occurs"""
+        return self._cache.get(key=item, read=True, retry=True)
+
+    def clear(self):
+        self._cache.clear()
+
+    def __len__(self):
+        return len(list(self._cache.iterkeys()))
+
+    def __contains__(self, item):
+        value = self._cache.get(item, retry=True)  # None, if expired
+        if value:
+            return True
+        return False
+
+    def __setitem__(self, key, value):
+        if not self.use_listings_cache:
+            return
+        self._cache.set(
+            key=key, value=value, expire=self.listings_expiry_time, retry=True
+        )
+
+    def __delitem__(self, key):
+        del self._cache[key]
+
+    def __iter__(self):
+        return (k for k in self._cache.iterkeys() if k in self)
+
+    def __reduce__(self):
+        return (
+            FileDirCache,
+            (self.use_listings_cache, self.listings_expiry_time, self.cache_location),
+        )

fsspec/implementations/http.py

@@ -102,6 +102,8 @@ def __init__(
         request_options.pop("listings_expiry_time", None)
         request_options.pop("max_paths", None)
         request_options.pop("skip_instance_cache", None)
+        request_options.pop("listings_cache_type", None)
+        request_options.pop("listings_cache_location", None)
         self.kwargs = request_options
 
         if not asynchronous:

fsspec/implementations/tests/test_http.py

@@ -170,14 +170,30 @@ def test_list_invalid_args(server):
         h.glob(server + "/index/*")
 
 
-def test_list_cache(server):
-    h = fsspec.filesystem("http", use_listings_cache=True)
+@pytest.mark.parametrize("listings_cache_type", ["memdircache", "filedircache"])
+def test_list_cache(server, listings_cache_type):
+    h = fsspec.filesystem(
+        "http", use_listings_cache=True, listings_cache_type=listings_cache_type
+    )
+
+    h.dircache.clear()  # Needed for filedircache
+
     out = h.glob(server + "/index/*")
     assert out == [server + "/index/realfile"]
 
+    h.dircache.clear()  # clean up
+
+
+@pytest.mark.parametrize("listings_cache_type", ["memdircache", "filedircache"])
+def test_list_cache_with_expiry_time_cached(server, listings_cache_type):
+    h = fsspec.filesystem(
+        "http",
+        use_listings_cache=True,
+        listings_expiry_time=30,
+        listings_cache_type=listings_cache_type,
+    )
 
-def test_list_cache_with_expiry_time_cached(server):
-    h = fsspec.filesystem("http", use_listings_cache=True, listings_expiry_time=30)
+    h.dircache.clear()  # Needed for filedircache
 
     # First, the directory cache is not initialized.
     assert not h.dircache
@@ -193,9 +209,19 @@ def test_list_cache_with_expiry_time_cached(server):
     out = h.glob(server + "/index/*")
     assert out == [server + "/index/realfile"]
 
+    h.dircache.clear()  # clean up
+
+
+@pytest.mark.parametrize("listings_cache_type", ["memdircache", "filedircache"])
+def test_list_cache_with_expiry_time_purged(server, listings_cache_type):
+    h = fsspec.filesystem(
+        "http",
+        use_listings_cache=True,
+        listings_expiry_time=0.3,
+        listings_cache_type=listings_cache_type,
+    )
 
-def test_list_cache_with_expiry_time_purged(server):
-    h = fsspec.filesystem("http", use_listings_cache=True, listings_expiry_time=0.3)
+    h.dircache.clear()  # Needed for filedircache
 
     # First, the directory cache is not initialized.
     assert not h.dircache
@@ -224,9 +250,20 @@ def test_list_cache_with_expiry_time_purged(server):
     cached_items = h.dircache.get(server + "/index/")
     assert len(cached_items) == 1
 
+    h.dircache.clear()  # clean up
 
-def test_list_cache_reuse(server):
-    h = fsspec.filesystem("http", use_listings_cache=True, listings_expiry_time=5)
+
+@pytest.mark.parametrize("listings_cache_type", ["memdircache", "filedircache"])
+def test_list_cache_reuse(server, listings_cache_type):
+    h = fsspec.filesystem(
+        "http",
+        use_listings_cache=True,
+        listings_expiry_time=5,
+        listings_cache_type=listings_cache_type,
+    )
+
+    # Needed for filedircache
+    h.dircache.clear()
 
     # First, the directory cache is not initialized.
     assert not h.dircache
@@ -245,14 +282,26 @@ def test_list_cache_reuse(server):
 
     # Verify that yet another new instance, with caching enabled,
     # will see the same cache content again.
-    h = fsspec.filesystem("http", use_listings_cache=True, listings_expiry_time=5)
+    h = fsspec.filesystem(
+        "http",
+        use_listings_cache=True,
+        listings_expiry_time=5,
+        listings_cache_type=listings_cache_type,
+    )
     assert len(h.dircache) == 1
 
     # However, yet another instance with a different expiry time will also not have
     # any valid cache content.
-    h = fsspec.filesystem("http", use_listings_cache=True, listings_expiry_time=666)
+    h = fsspec.filesystem(
+        "http",
+        use_listings_cache=True,
+        listings_expiry_time=666,
+        listings_cache_type=listings_cache_type,
+    )
     assert len(h.dircache) == 0
 
+    h.dircache.clear()  # clean up
+
 
 def test_ls_raises_filenotfound(server):
     h = fsspec.filesystem("http")
@@ -267,8 +316,14 @@ def test_list_cache_with_max_paths(server):
     assert out == [server + "/index/realfile"]
 
 
-def test_list_cache_with_skip_instance_cache(server):
-    h = fsspec.filesystem("http", use_listings_cache=True, skip_instance_cache=True)
+@pytest.mark.parametrize("listings_cache_type", ["memdircache", "filedircache"])
+def test_list_cache_with_skip_instance_cache(server, listings_cache_type):
+    h = fsspec.filesystem(
+        "http",
+        use_listings_cache=True,
+        skip_instance_cache=True,
+        listings_cache_type=listings_cache_type,
+    )
     out = h.glob(server + "/index/*")
     assert out == [server + "/index/realfile"]
 

fsspec/spec.py

@@ -10,7 +10,7 @@
 
 from .callbacks import _DEFAULT_CALLBACK
 from .config import apply_config, conf
-from .dircache import DirCache
+from .dircache import FileDirCache, MemDirCache
 from .transaction import Transaction
 from .utils import _unstrip_protocol, other_paths, read_block, stringify_path, tokenize
 
@@ -113,7 +113,7 @@ def __init__(self, *args, **storage_options):
         Parameters
         ----------
         use_listings_cache, listings_expiry_time, max_paths:
-            passed to ``DirCache``, if the implementation supports
+            passed to ``MemDirCache``, if the implementation supports
             directory listing caching. Pass use_listings_cache=False
             to disable such caching.
         skip_instance_cache: bool
@@ -130,7 +130,16 @@ def __init__(self, *args, **storage_options):
         self._intrans = False
         self._transaction = None
         self._invalidated_caches_in_transaction = []
-        self.dircache = DirCache(**storage_options)
+
+        listings_cache_type = storage_options.get("listings_cache_type", "memdircache")
+        if listings_cache_type not in ("memdircache", "filedircache"):
+            raise ValueError(
+                "'listings_cache_type' has to be one of ('memdircache', 'filedircache')"
+            )
+        if listings_cache_type == "memdircache":
+            self.dircache = MemDirCache(**storage_options)
+        else:
+            self.dircache = FileDirCache(**storage_options)
 
         if storage_options.pop("add_docs", None):
             warnings.warn("add_docs is no longer supported.", FutureWarning)

setup.py

@@ -54,6 +54,7 @@
         "fuse": ["fusepy"],
         "libarchive": ["libarchive-c"],
         "gui": ["panel"],
+        "dircache": ["diskcache", "appdirs"],
     },
     zip_safe=False,
 )

tox.ini

@@ -37,6 +37,8 @@ conda_deps=
     numpy
     nomkl
     jinja2
+    diskcache
+    appdirs
 deps=
     hadoop-test-cluster==0.1.0
     smbprotocol