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ARTS Week 39

凡事过往，皆为序章

Algoithm

从字符串生成二叉树

概述

你需要从一个包括括号和整数的字符串构建一棵二叉树。

输入的字符串代表一棵二叉树。它包括整数和随后的 0 ，1 或 2 对括号。整数代表根的值，一对括号内表示同样结构的子树。

若存在左子结点，则从左子结点开始构建。

示例：

输入："4(2(3)(1))(6(5))"
输出：返回代表下列二叉树的根节点:

       4
     /   \
    2     6
   / \   /
  3   1 5

提示：

输入字符串中只包含'(', ')', '-'和'0' ~ '9'

空树由""而非"()"表示。

分析

二叉树的题目，总体按照先序/中序/后序 方式进行递归生成。

  1. 首先判断终止条件：

    1. 如果为 "" ，则为 root
    2. 如果没有 "("，那么说明完整组成 root节点

  2. 进行左右子树分割

    1. 按照格"()" 进行切割
    2. 如果组合为0，且开始节点保持一致，那么就说明是左子树，否则为右子树。

  3. 递归生成

code

# Definition for a binary tree node.
class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right


class Solution:
    def str2tree(self, s: str) -> TreeNode:
        root = self.dfs(s)
        return root

    def dfs(self, s):
        if len(s) == 0:
            return None
        if '(' not in s:
            return TreeNode(int(s[:]))
        pos = s.index('(')
        root = TreeNode(int(s[0: pos]))
        start = pos  # （start是某棵子树，区间的起始index，第一个左括号）
        cnt = 0
        for i in range(pos, len(s)):
            if s[i] == '(':
                cnt += 1
            elif s[i] == ')':
                cnt -= 1

            if cnt == 0 and start == pos:  # 左子的部分
                root.left = self.str2tree(s[start + 1: i])
                start = i + 1
            elif cnt == 0 and start != pos:  # 右子的部分 这个地方必须用 elif!!!!!!
                root.right = self.str2tree(s[start + 1: i])

        return root

Review

[Tutorial, Part 1] How to develop Go gRPC microservice with HTTP/REST endpoint, middleware, Kubernetes deployment, etc.

概述

I want to provide step by step tutorial how to develop simple CRUD “To Do list” microservice with gRPC and HTTP/REST endpoints. I demonstrate how to write tests and add middleware (request-ID and logging/tracing) to microservice also. I provide example how to build and deploy this microservice to Kubernetes at the end.

Table of Content

  1. about how to create gRPC CRUD service and client
  2. about how to add HTTP/REST endpoint to the gRPC service
  3. about how to add middleware (e.g. logging/tracing) to gRPC service and HTTP/REST endpoint as well
  4. going to be dedicated how to add Kubernetes deployment configuration with health check and how to build and deploy project to Google Cloud

create gRPC CRUD service

  1. https://github.com/amsokol/go-grpc-http-rest-microservice-tutorial/tree/part1
  2. https://github.com/golang-standards/project-layout

Tip

推荐阅读：分布式系统架构经典资料

概述

分布式框架的相关资料汇总

基础概念

  • CAP 定理
  • Fallacies of Distributed Computing

经典资料

  • Distributed systems theory for the distributed systems engineer

  • FLP Impossibility Result

  • An introduction to distributed systems

  • Distributed Systems for fun and profit

  • Distributed Systems: Principles and Paradigms

  • Scalable Web Architecture and Distributed Systems

  • Principles of Distributed Systems

  • Making reliable distributed systems in the presence of software errors

  • Designing Data Intensive Applications

CAP 定理

CAP 定理是分布式系统设计中最基础，也是最为关键的理论。它指出，分布式数据存储不可能同时满足以下三个条件。

  • 一致性（Consistency）：每次读取要么获得最近写入的数据，要么获得一个错误。
  • 可用性（Availability）：每次请求都能获得一个（非错误）响应，但不保证返回的是最新写入的数据。
  • 分区容忍（Partition tolerance）：尽管任意数量的消息被节点间的网络丢失（或延迟），系统仍继续运行。

错误假设

  1. 网络是稳定的。网络传输的延迟是零。
  2. 网络的带宽是无穷大。网络是安全的。
  3. 网络的拓扑不会改变。
  4. 只有一个系统管理员。
  5. 传输数据的成本为零。
  6. 整个网络是同构的。

资料总结

Distributed systems theory for the distributed systems engineer

Distributed Systems for Fun and Profit 这是一本小书，涵盖了分布式系统中的关键问题，包括时间的作用和不同的复制策略。后文中对这本书有较详细的介绍。

Notes on distributed systems for young bloods ，这篇文章中没有理论，是一份适合新手阅读的分布式系统实践笔记。

A Note on Distributed Systems ，这是一篇经典的论文，讲述了为什么在分布式系统中，远程交互不能像本地对象那样进行。

The fallacies of distributed computing ，每个分布式系统新手都会做的 8 个错误假设，并探讨了其会带来的影响。上文中专门对这篇文章做了介绍。

Share

ORM简单的模板-Python

概述

整理了部分基于 ORM框架的同步/异步 相关组建。

PSql

import os
import asyncio
import inspect
import functools
import collections

import orjson
from blinker import signal
from sqlalchemy import exc, event, create_engine
from sqlalchemy.engine.base import Engine as SQLAlchemyEngine
from sqlalchemy.orm import UOWTransaction, sessionmaker, scoped_session
from sqlalchemy.pool import NullPool
from sqlalchemy.ext.asyncio import AsyncSession as _AsyncSession
from sqlalchemy.ext.asyncio import create_async_engine, async_scoped_session

# 相关的设置
from settings import DB_DSN, DB_POOL_SIZE, DB_MAX_OVERFLOW, DB_POOL_RECYCLE

engine: SQLAlchemyEngine = create_engine(
    DB_DSN,
    pool_size=DB_POOL_SIZE,
    max_overflow=DB_MAX_OVERFLOW,
    pool_recycle=DB_POOL_RECYCLE,
    json_serializer=lambda obj: orjson.dumps(obj).decode(),
    json_deserializer=lambda obj: orjson.loads(obj),
)

# Constructs a scoped DBSession.
Session = scoped_session(
    sessionmaker(engine, expire_on_commit=False, future=True),
)


@event.listens_for(engine, "connect")
def connect(dbapi_connection, connection_record):
    connection_record.info["pid"] = os.getpid()


@event.listens_for(engine, "checkout")
def checkout(dbapi_connection, connection_record, connection_proxy):
    pid = os.getpid()
    if connection_record.info["pid"] != pid:
        connection_record.connection = connection_proxy.connection = None
        raise exc.DisconnectionError(
            "Connection record belongs to pid %s, "
            "attempting to check out in pid %s" % (connection_record.info["pid"], pid)
        )


@event.listens_for(Session, "after_flush")
def after_flush(session, flush_context: UOWTransaction):
    if not hasattr(session, "g_changed_track_info"):
        session.g_changed_track_info = collections.defaultdict(set)

    for instances in flush_context.mappers.values():
        for instance in instances:
            session.g_changed_track_info[instance.class_.__name__].add(
                instance.identity
            )


@event.listens_for(Session, "after_commit")
def after_commit(session):
    if not hasattr(session, "g_changed_track_info"):
        return

    for model_name, primary_keys in session.g_changed_track_info.items():
        signal(model_name).send(primary_keys)
    delattr(session, "g_changed_track_info")


async_engine = create_async_engine(
    DB_DSN.replace("psycopg2", "asyncpg"),
    json_serializer=lambda obj: orjson.dumps(obj).decode(),
    json_deserializer=lambda obj: orjson.loads(obj),
    poolclass=NullPool,
)

_session_factory = sessionmaker(
    async_engine, expire_on_commit=False, class_=_AsyncSession
)


def _hooked_session_maker():
    async_session = _session_factory()

    @event.listens_for(async_session.sync_session, "after_flush")
    def _after_flush(session, flush_context: UOWTransaction):
        if not hasattr(session, "g_changed_track_info"):
            session.g_changed_track_info = collections.defaultdict(set)

        for instances in flush_context.mappers.values():
            for instance in instances:
                session.g_changed_track_info[instance.class_.__name__].add(
                    instance.identity
                )

    @event.listens_for(async_session.sync_session, "after_commit")
    def _after_commit(session):
        if not hasattr(session, "g_changed_track_info"):
            return

        for model_name, primary_keys in session.g_changed_track_info.items():
            signal(model_name).send(primary_keys)
        delattr(session, "g_changed_track_info")

    return async_session


AsyncSession = async_scoped_session(
    _hooked_session_maker,
    scopefunc=asyncio.current_task,
)


def session_scope(fn):
    """Defines session top level life time, session will be closed after scope ends."""

    if inspect.iscoroutinefunction(fn):

        @functools.wraps(fn)
        async def wrapper_decorator(*args, **kwargs):
            async with AsyncSession():
                return await fn(*args, **kwargs)

    else:

        @functools.wraps(fn)
        def wrapper_decorator(*args, **kwargs):
            with Session():
                return fn(*args, **kwargs)

    return wrapper_decorator


def commit_scope(fn):
    """Defines transaction top level life time, force begin /close transaction."""

    if inspect.iscoroutinefunction(fn):

        @functools.wraps(fn)
        async def wrapper_decorator(*args, **kwargs):
            session = AsyncSession()
            try:
                res = await fn(*args, **kwargs)
                await session.commit()
                return res

            except Exception:
                await session.rollback()
                raise

    else:

        @functools.wraps(fn)
        def wrapper_decorator(*args, **kwargs):
            session = Session()
            try:
                res = fn(*args, **kwargs)
                session.commit()
                return res
            except Exception:
                session.rollback()
                raise

    return wrapper_decorator