[enh] add searx.shared

shared dictionary between the workers (UWSGI or werkzeug)
scheduler: run a task once every x seconds (UWSGI or werkzeug)

searx/shared/__init__.py

@@ -0,0 +1,31 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+import logging
+
+logger = logging.getLogger('searx.shared')
+
+try:
+    import uwsgi
+except:
+    # no uwsgi
+    from .shared_simple import SimpleSharedDict as SharedDict, schedule
+    logger.info('Use shared_simple implementation')
+else:
+    try:
+        uwsgi.cache_update('dummy', b'dummy')
+        if uwsgi.cache_get('dummy') != b'dummy':
+            raise Exception()
+    except:
+        # uwsgi.ini configuration problem: disable all scheduling
+        logger.error('uwsgi.ini configuration error, add this line to your uwsgi.ini\n'
+                     'cache2 = name=searxcache,items=2000,blocks=2000,blocksize=4096,bitmap=1')
+        from .shared_simple import SimpleSharedDict as SharedDict
+
+        def schedule(delay, func, *args):
+            pass
+    else:
+        # uwsgi
+        from .shared_uwsgi import UwsgiCacheSharedDict as SharedDict, schedule
+        logger.info('Use shared_uwsgi implementation')
+
+storage = SharedDict()