[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/shared_uwsgi.py

@@ -0,0 +1,62 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+import time
+import uwsgi  # pylint: disable=E0401
+from . import shared_abstract
+
+
+_last_signal = 10
+
+
+class UwsgiCacheSharedDict(shared_abstract.SharedDict):
+
+    def get_int(self, key):
+        value = uwsgi.cache_get(key)
+        if value is None:
+            return value
+        else:
+            return int.from_bytes(value, 'big')
+
+    def set_int(self, key, value):
+        b = value.to_bytes(4, 'big')
+        uwsgi.cache_update(key, b)
+
+    def get_str(self, key):
+        value = uwsgi.cache_get(key)
+        if value is None:
+            return value
+        else:
+            return value.decode('utf-8')
+
+    def set_str(self, key, value):
+        b = value.encode('utf-8')
+        uwsgi.cache_update(key, b)
+
+
+def schedule(delay, func, *args):
+    """
+    Can be implemented using a spooler.
+    https://uwsgi-docs.readthedocs.io/en/latest/PythonDecorators.html
+
+    To make the uwsgi configuration simple, use the alternative implementation.
+    """
+    global _last_signal
+
+    def sighandler(signum):
+        now = int(time.time())
+        uwsgi.lock()
+        try:
+            updating = uwsgi.cache_get('updating')
+            if updating is not None:
+                updating = int.from_bytes(updating, 'big')
+                if now - updating < delay:
+                    return
+            uwsgi.cache_update('updating', now.to_bytes(4, 'big'))
+        finally:
+            uwsgi.unlock()
+        func(*args)
+
+    signal_num = _last_signal
+    _last_signal += 1
+    uwsgi.register_signal(signal_num, 'worker', sighandler)
+    uwsgi.add_timer(signal_num, delay)