Implement block transfer logic

observer.py

@@ -0,0 +1,31 @@
+from multiprocessing import Lock, Queue
+
+class Observer:
+    def __init__(self):
+        self.__receivers_list = {}
+        self.__lock = Lock()
+    def listen(self, identifier):
+        with self.__lock:
+            queue = Queue()
+            self.__receivers_list.setdefault(identifier, set())
+            self.__receivers_list[identifier].add(queue)
+            return Subscription(self, identifier, queue)
+    def publish(self, identifier, message):
+        if identifier in self.__receivers_list:
+            for queue in self.__receivers_list[identifier]:
+                queue.put(message)
+    def quit(self, identifer, queue):
+        with self.__lock:
+            self.__receivers_list[identifer].remove(queue)
+            if len(self.__receivers_list[identifer]) == 0:
+                del self.__receivers_list[identifer]
+
+class Subscription:
+    def __init__(self, observer, identifier, queue):
+        self.__observer = observer
+        self.__identifier = identifier
+        self.__queue = queue
+    def receive(self, timeout):
+        return self.__queue.get(timeout=timeout)
+    def __del__(self):
+        self.__observer.quit(self.__identifier, self.__queue)