V1 DONE

MP2/peer.py

@@ -8,8 +8,8 @@ import json
 def utc_time():
     return datetime.now(timezone.utc).timestamp()
 
-INTRODUCER_IP = "172.22.156.3"
+INTRODUCER_IP = "172.22.156.3" #hardcoded ip
-IP = socket.gethostbyname(socket.gethostname())
+IP = socket.gethostbyname(socket.gethostname()) #the vm IP address
 SERVER_PORT = 8989
 INTRODUCER_FLAG = (INTRODUCER_IP == IP)
 HEART_BEAT_INTERVAL = 0.25
@@ -19,10 +19,25 @@ FAILURE_T_CLEANUP = 10.0
 RETRY_INTERVAL = 5.0
 FANOUT = 1
 
+#message json example:
+# {
+#     type: "GOSSIP", or "JOIN", ...
+#     sender_id: (ip, port, timestamp),
+#     members: [
+#         {
+#             ip: "
+#             port: 8989,
+#             timestamp: 1234567890.123456,
+#             heart_beat: 1,
+#             state: "alive"
+#         },
+#         ...
+
 members_list = {}
-dead_members = set()
+dead_members = set() #[BASICALLY VERSION TRACKING]this tracks members that have been marked as failed and removed from the membership list.
 members_list_lock = threading.Lock()
 
+#adding its self to the membership list
 SELF_ID = (IP, SERVER_PORT, utc_time())
 members_list[SELF_ID] = {
     "heart_beat": 1,
@@ -31,19 +46,21 @@ members_list[SELF_ID] = {
     "local_failed_since" : None,
     "local_suspected_since" : None
 }
-print(f"Starting peer: IP={IP}, port={SERVER_PORT}, introducer={INTRODUCER_FLAG}, self_id={SELF_ID}")
 
-stop_event = threading.Event()
+stop_event = threading.Event() #trigger to stop all threads when the program is exiting
 
+#one socket for all threads to use
 server_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
 server_socket.bind((IP, SERVER_PORT))
 server_socket.settimeout(1.0)
 
+#responsible for handling incoming gossip messages, join requests on the introducer, and updating the membership list based on the received messages
 def worker_1():
-    has_joined = INTRODUCER_FLAG
+    has_joined = INTRODUCER_FLAG #if this is the introducer, it has already joined
-    last_join_time = 0
+    last_join_time = 0 #flag to track the last time a join request was sent to retry
     
     while not stop_event.is_set():
+        # If the node has not joined and enough time has passed since the last join attempt, send a JOIN request to the introducer
         if not has_joined and (utc_time() - last_join_time > RETRY_INTERVAL):
             join_payload = {
                 "type": "JOIN",
@@ -59,11 +76,13 @@ def worker_1():
                 
             msg_type = msg.get("type")
             
+            #handle join type
             if msg_type == "JOIN":
                 join_ip, join_port, join_timestamp = msg["sender_id"]
                 join_id = (join_ip, join_port, join_timestamp)
                 
                 with members_list_lock:
+                    #if in dead members, ignore the join request
                     if join_id in dead_members:
                         continue
 
@@ -75,7 +94,6 @@ def worker_1():
                             "local_failed_since" : None,
                             "local_suspected_since" : None
                         }
-                        print(f"Added member: {join_id}")
                     
                     members_payload = []
                     for m_id, m_data in members_list.items():
@@ -87,15 +105,17 @@ def worker_1():
                             "state": m_data["state"]
                         })
                 
+                #send the current membership list to the joining node
                 reply_payload = {
                     "type": "GOSSIP",
                     "sender_id": SELF_ID,
                     "members": members_payload
                 }
                 server_socket.sendto(json.dumps(reply_payload).encode('utf-8'), (join_ip, join_port))
-                print(f"Sent initial membership state to {(join_ip, join_port)}")
 
+            #handle gossip type
             elif msg_type == "GOSSIP":
+                #first time receiving a gossip message, mark the node as joined
                 if not has_joined:
                     has_joined = True
 
@@ -105,32 +125,27 @@ def worker_1():
                     for member in members_json:
                         member_id = (member['ip'], member['port'], member['timestamp'])
                         
-                        if member_id == SELF_ID:
+                        if member_id == SELF_ID or member_id in dead_members:
                             continue
 
                         incoming_state = member['state']
                         incoming_hb = member['heart_beat']
                             
-                        if member_id in dead_members:
+                        local_member = members_list[member_id]
-                            continue
-
-                        if member_id not in members_list:
 
+                        if local_member is None:
                             if incoming_state == "failed":
                                 dead_members.add(member_id)
-                                continue
+                            else:
-
+                                members_list[member_id] = {
-                            members_list[member_id] = {
+                                    "heart_beat": incoming_hb,
-                                "heart_beat": incoming_hb,
+                                    "local_last_seen": utc_time(),
-                                "local_last_seen": utc_time(),
+                                    "state": incoming_state,
-                                "state": incoming_state,
+                                    "local_failed_since" : None,
-                                "local_failed_since": None,
+                                    "local_suspected_since" : None
-                                "local_suspected_since": None
+                                }
-                            }
                             continue
 
-                        local_member = members_list[member_id]
-
                         if local_member["state"] == "failed":
                             continue
 
@@ -145,12 +160,14 @@ def worker_1():
         except socket.timeout:
             continue
 
+#handles incrementing the local node's heartbeat counter at regular intervals
 def worker_2():
     while not stop_event.is_set():
         with members_list_lock:
             members_list[SELF_ID]["heart_beat"] += 1
         time.sleep(HEART_BEAT_INTERVAL)
 
+#handles sending gossip messages to a subset of alive peers at regular intervals
 def worker_3():
     peer_queue = []
     
@@ -169,14 +186,13 @@ def worker_3():
                 })
         
         if current_peers:
-            # Clean up peers from queue that might have failed or left
+            #remove any peers from the queue that are no longer alive 
             peer_queue = [p for p in peer_queue if p in current_peers]
             
             selected_peers = []
             num_to_select = min(FANOUT, len(current_peers))
             
             for _ in range(num_to_select):
-                # Reshuffle if the queue is empty
                 if not peer_queue:
                     peer_queue = list(current_peers)
                     random.shuffle(peer_queue)
@@ -198,6 +214,7 @@ def worker_3():
             
         time.sleep(GOSSIP_INTERVAL)
 
+# handle failure detection and cleanup of failed members from the membership list
 def worker_4():
     while not stop_event.is_set():
         current_time = utc_time()
@@ -226,6 +243,7 @@ def worker_4():
                 
         time.sleep(0.5)
 
+#for monitoring purposes
 def worker_monitoring():
     while not stop_event.is_set():
         with members_list_lock: