时间戳理解笔记

# Twitter's Snowflake algorithm implementation which is used to generate distributed IDs.
# https://github.com/twitter-archive/snowflake/blob/snowflake-2010/src/main/scala/com/twitter/service/snowflake/IdWorker.scala

import time
import logging

from .exceptions import InvalidSystemClock


# 64位ID的划分
WORKER_ID_BITS = 5  # 节点ID长度，某个数据中心的机器ID
DATACENTER_ID_BITS = 5  # 数据中心ID长度，可理解为不同地点
SEQUENCE_BITS = 12  # 序列号12位，同一个机器同一毫秒最多记录4095个

# 最大取值计算
MAX_WORKER_ID = -1 ^ (-1 << WORKER_ID_BITS)  # 2**5-1 0b11111  最大支持机器节点数0~31，一共32个
MAX_DATACENTER_ID = -1 ^ (-1 << DATACENTER_ID_BITS)  # 最大支持数据中心节点数0~31，一共32个

# 移位偏移计算
WOKER_ID_SHIFT = SEQUENCE_BITS  # 机器节点左移12位
DATACENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS  # 数据中心节点左移17位
TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATACENTER_ID_BITS  # 时间毫秒数左移22位

# 序号循环掩码
SEQUENCE_MASK = -1 ^ (-1 << SEQUENCE_BITS)

# Twitter元年时间戳
TWEPOCH = 1288834974657  # 标记时间,13位


logger = logging.getLogger('flask.app')


class IdWorker(object):
    """
    用于生成IDs
    """

    def __init__(self, datacenter_id, worker_id, sequence=0):
        """
        初始化
        :param datacenter_id: 数据中心（机器区域）ID
        :param worker_id: 机器ID
        :param sequence: 起始序号
        """
        # sanity check
        if worker_id > MAX_WORKER_ID or worker_id < 0:
            raise ValueError('worker_id值越界')

        if datacenter_id > MAX_DATACENTER_ID or datacenter_id < 0:
            raise ValueError('datacenter_id值越界')

        self.worker_id = worker_id
        self.datacenter_id = datacenter_id
        self.sequence = sequence

        self.last_timestamp = -1  # 上次计算的时间戳

    def _gen_timestamp(self):
        """
        生成整数时间戳
        :return:int timestamp
        """
        return int(time.time() * 1000)

    def get_id(self):
        """
        获取新ID
        :return:
        """
        # 生成整数时间戳
        timestamp = self._gen_timestamp()

        # 时钟回拨
        if timestamp < self.last_timestamp:
            logging.error('clock is moving backwards. Rejecting requests until {}'.format(self.last_timestamp))
            raise InvalidSystemClock

        if timestamp == self.last_timestamp:
            self.sequence = (self.sequence + 1) & SEQUENCE_MASK
            if self.sequence == 0:
                timestamp = self._til_next_millis(self.last_timestamp)
        else:
            self.sequence = 0

        self.last_timestamp = timestamp
        # new_id = ((时间戳-标记时间）41位，1位占位符 << 左位移22位补成64位bit）|（区域ID 5位 << 左位移17位）|（机器ID 5位 <<左位移12位）| 序列号12位
        # | 或，或0,得原来值，即并上
        new_id = ((timestamp - TWEPOCH) << TIMESTAMP_LEFT_SHIFT) | (self.datacenter_id << DATACENTER_ID_SHIFT) | \
                 (self.worker_id << WOKER_ID_SHIFT) | self.sequence
        return new_id

    def _til_next_millis(self, last_timestamp):
        """
        等到下一毫秒
        """
        timestamp = self._gen_timestamp()
        while timestamp <= last_timestamp:
            timestamp = self._gen_timestamp()
        return timestamp


if __name__ == '__main__':
    worker = IdWorker(1, 2, 0)
    print(worker.get_id())
``