確保enqueue的atomic

atomic.py

import redis

r = redis.Redis(host='localhost', port=6379, db=0)

lua_script = """
local queue_length = redis.call('llen', KEYS[1])
if queue_length > 0 then
    -- get the last number
    local last_number = redis.call('lindex', KEYS[1], -1)
    local new_number = tonumber(last_number) + 1
    -- add new number to the queue
    redis.call('rpush', KEYS[1], new_number)
    -- return the new number and the queue length
    return {new_number, queue_length}
else
    -- handle empty queue exception
    return {nil, 0}
end
"""

queue_name = f'waiting:store:{3}:capacity:{2}'
result = r.eval(lua_script, 1, queue_name)
new_number, queue_length = result[0], result[1]

if new_number:
    print(f"下一個號碼是: {new_number}, 當前等待桌數: {queue_length}")
else:
    # handle_empty_queue_exception()

singleton.py

class Singleton:
    _instance = None # 底線表示 private

    @classmethod
    def get_instance(cls):
        if not cls._instance:
            # 如果不存在，則創建一個新的instance
            cls._instance = cls()
        return cls._instance