Make various global caches used by the server thread-safe

src/calibre/srv/content.py

@@ -8,6 +8,7 @@ __copyright__ = '2015, Kovid Goyal <kovid at kovidgoyal.net>'
 
 import os
 from io import BytesIO
+from threading import Lock
 
 from calibre import fit_image
 from calibre.constants import config_dir
@@ -27,6 +28,7 @@ from calibre.utils.magick.draw import thumbnail, Image
 plugboard_content_server_value = 'content_server'
 plugboard_content_server_formats = ['epub', 'mobi', 'azw3']
 update_metadata_in_fmts = frozenset(plugboard_content_server_formats)
+lock = Lock()
 
 # Get book formats/cover as a cached filesystem file {{{
 
@@ -45,6 +47,8 @@ def create_file_copy(ctx, rd, prefix, library_id, book_id, ext, mtime, copy_func
     fname = os.path.join(base, bname)
     do_copy = True
     mtime = timestampfromdt(mtime)
+
+    # TODO: Implement locking for this cache
     try:
         ans = lopen(fname, 'r+b')
         do_copy = os.fstat(ans.fileno()).st_mtime < mtime
@@ -167,6 +171,7 @@ def icon(ctx, rd, which):
             return lopen(path, 'rb')
         except EnvironmentError:
             raise HTTPNotFound()
+    with lock:
         tdir = os.path.join(rd.tdir, 'icons')
         cached = os.path.join(tdir, '%d-%s.png' % (sz, which))
         try:

src/calibre/srv/handler.py

@@ -67,6 +67,7 @@ class Context(object):
         self.opts = opts
         self.library_broker = LibraryBroker(libraries)
         self.testing = testing
+        self.lock = Lock()
 
     def init_session(self, endpoint, data):
         pass
@@ -80,6 +81,7 @@ class Context(object):
     def allowed_book_ids(self, data, db):
         # TODO: Implement this based on data.username caching result on the
         # data object
+        with self.lock:
             ans = data.allowed_book_ids.get(db.server_library_id)
             if ans is None:
                 ans = data.allowed_book_ids[db.server_library_id] = db.all_book_ids()
@@ -88,6 +90,7 @@ class Context(object):
     def get_categories(self, data, db, restrict_to_ids=None):
         if restrict_to_ids is None:
             restrict_to_ids = self.allowed_book_ids(data, db)
+        with self.lock:
             cache = self.library_broker.category_caches[db.server_library_id]
             old = cache.pop(restrict_to_ids, None)
             if old is None or old[0] <= db.last_modified():
@@ -102,6 +105,7 @@ class Context(object):
     def search(self, data, db, query, restrict_to_ids=None):
         if restrict_to_ids is None:
             restrict_to_ids = self.allowed_book_ids(data, db)
+        with self.lock:
             cache = self.library_broker.search_caches[db.server_library_id]
             key = (query, restrict_to_ids)
             old = cache.pop(key, None)