Implement Monotonic Clock Wrapper - The Timekeeper

                      TASK
                    

Implementation

A MonotonicClock wraps the system clock and guarantees the returned value never decreases. Implement this wrapper and track what information is lost.

Request:  {"type": "mono_read", "msg_id": 1}
Response: {"type": "mono_read_ok", "in_reply_to": 1, "time_ms": 1234567, "corrections": 0}

Sample Test Cases

Mono read returns timeTimeout: 5000ms

Input

{"src":"c0","dest":"n1","body":{"type":"init","msg_id":1,"node_id":"n1","node_ids":["n1"]}}
{"src":"c1","dest":"n1","body":{"type":"mono_read","msg_id":2}}

Expected Output

{"src": "n1", "dest": "c0", "body": {"type": "init_ok", "in_reply_to": 1, "msg_id": 0}}

Two reads are non-decreasingTimeout: 5000ms

Input

{"src":"c0","dest":"n1","body":{"type":"init","msg_id":1,"node_id":"n1","node_ids":["n1"]}}
{"src":"c1","dest":"n1","body":{"type":"mono_read","msg_id":2}}
{"src":"c1","dest":"n1","body":{"type":"mono_read","msg_id":3}}

Expected Output

{"src": "n1", "dest": "c0", "body": {"type": "init_ok", "in_reply_to": 1, "msg_id": 0}}

Hints

Hint 1▾

Wrap the system clock to always return >= previous value

Hint 2▾

Use max(current, last_returned) as the strategy

Hint 3▾

Track how many times the wrapper prevented a backward jump

Hint 4▾

Information lost: you cannot detect when time actually went backward

Hint 5▾

time.monotonic() in Python provides this natively

Resources

Monotonic Clocks

Python docs on monotonic clock guarantees

                      OVERVIEW
                    

Theoretical Hub

Concept overview coming soon

Key Concepts

monotonic clockclock wrapperinformation lossordering guarantee

main.py

python

#!/usr/bin/env python3
import sys, json, time
class MonotonicClock:
    def __init__(self): self.last = 0; self.corrections = 0
    def read(self, raw_ms):
        # TODO: Return max(raw_ms, self.last), track corrections
        pass
class Node:
    def __init__(self):
        self.node_id=None;self.node_ids=[];self.next_msg_id=0;self.
        clock=MonotonicClock();self.offset=0
    def send(self,d,b):b["msg_id"]=self.next_msg_id;self.next_msg_id+=1;print
    (json.dumps({"src":self.node_id,"dest":d,"body":b}),flush=True)
    def reply(self,r,b):b["in_reply_to"]=r["body"]["msg_id"];self.send(r
    ["src"],b)
    def now_ms(self):return int(time.time()*1000)+self.offset
def main():
    node=Node()
    for line in sys.stdin:
        line=line.strip()
        if not line:continue
        msg=json.loads(line);body=msg["body"];t=body["type"]
        if t=="init":node.node_id=body["node_id"];node.node_ids=body
        ["node_ids"];node.reply(msg,{"type":"init_ok"})
        elif t=="mono_read":pass
        elif t=="simulate_ntp":node.offset+=body["offset_ms"];node.reply(msg,
        {"type":"simulate_ntp_ok"})
if __name__=="__main__":main()