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Ensure that updating the vl_book cache is both thread safe and recursion safe.

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This commit is contained in:
Charles Haley 2021-05-05 18:59:45 +01:00
parent 0a6010e712
commit 312e44dc3b
1 changed files with 31 additions and 22 deletions
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53
src/calibre/db/cache.py
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@ -15,6 +15,7 @@ import traceback
from collections import MutableSet, Set, defaultdict
from functools import partial, wraps
from io import BytesIO
from threading import Lock
from time import time
from calibre import as_unicode, isbytestring
@ -142,7 +143,7 @@ class Cache(object):
self.formatter_template_cache = {}
self.dirtied_cache = {}
self.vls_for_books_cache = None
self.vls_for_books_cache_is_loading = False
self.vls_cache_lock = Lock()
self.dirtied_sequence = 0
self.cover_caches = set()
self.clear_search_cache_count = 0
@ -252,7 +253,6 @@ class Cache(object):
self.clear_search_cache_count += 1
self._search_api.update_or_clear(self, book_ids)
self.vls_for_books_cache = None
self.vls_for_books_cache_is_loading = False
@read_api
def last_modified(self):
@ -2232,26 +2232,35 @@ class Cache(object):
if self.vls_for_books_cache is None:
# Using a list is slightly faster than a set.
c = defaultdict(list)
if self.vls_for_books_cache_is_loading:
# We get here if resolving the books in a VL triggers another VL
# calculation. This can be 'real' recursion, in which case the
# eventual answer will be wrong. It can also be a search using
# a location of 'all' that causes evaluation of a composite that
# references virtual libraries. If the composite isn't used in a
# VL then the eventual answer will be correct because get_metadata
# will clear the caches.
return c
self.vls_for_books_cache_is_loading = True
libraries = self._pref('virtual_libraries', {})
for lib, expr in libraries.items():
book = None
try:
for book in self._search(expr, virtual_fields=virtual_fields):
c[book].append(lib)
except Exception as e:
if book:
c[book].append(_('[Error in Virtual library {0}: {1}]').format(lib, str(e)))
self.vls_for_books_cache = {b:tuple(sorted(libs, key=sort_key)) for b, libs in c.items()}
got_lock = False
try:
# use a primitive lock to ensure that only one thread is updating
# the cache and that recursive calls don't do the update. This
# method can recurse via self._search()
got_lock = self.vls_cache_lock.acquire(blocking=False)
if not got_lock:
# We get here if resolving the books in a VL triggers another VL
# calculation. This can be 'real' recursion, in which case the
# eventual answer will be wrong. It can also be a search using
# a location of 'all' that causes evaluation of a composite that
# references virtual_libraries(). If the composite isn't used in a
# VL then the eventual answer will be correct because get_metadata
# will clear the caches.
return c
self.vls_for_books_cache_is_loading = True
libraries = self._pref('virtual_libraries', {})
for lib, expr in libraries.items():
book = None
try:
for book in self._search(expr, virtual_fields=virtual_fields):
c[book].append(lib)
except Exception as e:
if book:
c[book].append(_('[Error in Virtual library {0}: {1}]').format(lib, str(e)))
self.vls_for_books_cache = {b:tuple(sorted(libs, key=sort_key)) for b, libs in c.items()}
finally:
if got_lock:
self.vls_cache_lock.release()
if not book_ids:
book_ids = self._all_book_ids()
# book_ids is usually 1 long. The loop will be faster than a comprehension