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‎docs/blog/posts/code-complete.md

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draft: false
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authors: [huyi]
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date: 2024-08-10
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slug: chance
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slug: code-complete
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description: 记录并总结常见技术概念和技术知识。
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以下所言，或来自读书笔记，或来自书籍的勾画，或只是回忆...作为参考。
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categories:
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- 学习笔记

‎docs/blog/posts/java-concurrent.md

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---
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title: Java-Concurrent
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draft: false
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authors: [huyi]
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date: 2024-09-12
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slug: juc
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description: 关于Java并发编程的一些知识总结与整理
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以下所言，或来自读书笔记，或来自书籍的勾画，或只是回忆...作为参考。
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categories:
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- 学习笔记
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- 并发
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- Java
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---
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关于Java并发编程的一些知识总结与整理。 <!-- more -->
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# Java并发
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## 乐观锁与悲观锁
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现实生活中，有资源就有竞争，我认为锁就是对有限资源的一种争取；程序中的锁也是一样，对共享资源（内容）进行操作，需要保证操作的安全性，即保证共享资源的完整性和一致性。
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- **乐观锁**：认为共享资源每次访问的时候都不会出问题，不需要加锁，只需要**在提交修改时再判断对应的资源是否符合预期**（即在最终操作数据时做校验，而不是一上来就认为不行）。具体可以使用**数据库版本号或CAS技术**来实现。
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- **悲观锁**：认为共享资源每次访问时都会有问题，所以**每次获取数据都需要加锁（独享）**，直到自己操作完成后释放锁之后，其他线程才可以进行操作。Java中的`synchronized`和`ReentrantLock`等独占锁就是悲观锁思想的实现。
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## CAS
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**CAS（compare and swap）**是一种**乐观锁**的实现方式，全称是"**比较并交换**"，是Java中一种**无锁的原子性操作**。
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CAS操作包含**三**个操作数——内存位置（V）、期望的原值（A）和新值（B）。
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**工作原理**：当且仅当内存位置V的值等于预期原值A时，将该内存位置V的值替换为新值B。并且整个比较和更新操作都是原子操作。
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> 无锁：指的是不通过锁机制对共享数据来实现线程安全
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`java.util.concurrent.atomic`包下提供了一系列原子类（e.g. AtomicInteger、AtomicLong），它们内部都使用CAS操作来保证线程安全。底层通过sun.misc.Unsafe#compareAndSetInt方法实现（注：该方法是native方法）。
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或者说CAS机制其实是通过`native boolean compareAndSetInt()`方法实现的，AtomicLong底层调用了该方法。
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## 线程池
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> 背景：当任务比较繁重，线程创建过多会带来调度开销，即线程的频繁创建与销毁，类似于TCP连接的频繁创建与销毁
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线程池是一种线程使用模式，线程池中维护着多个线程，等待调度器分配可并发执行的任务，避免了在处理短时间任务时创建与销毁线程的代价。
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特点/好处：
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- **降低资源消耗**：重复利用已创建的线程来避免频繁的线程创建和销毁造成的消耗
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- **提高响应速度**：当出现可执行任务时，不需要等待线程的创建，任务可以立马被执行
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- **提高线程的可管理性**：线程是稀缺资源，如果无节制的创建，不仅会消耗系统资源，还会降低系统的稳定性，使用线程池可以进行统一的分配，调优和监控

‎docs/index.md

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# About
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For full documentation visit [mkdocs.org](https://www.mkdocs.org).
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Hello，Welcome to cxyhuky's blog.
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## Commands
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I am a server-side programmer.
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* `mkdocs new [dir-name]` - Create a new project.
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* `mkdocs serve` - Start the live-reloading docs server.
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* `mkdocs build` - Build the documentation site.
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* `mkdocs -h` - Print help message and exit.
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这只是一个开始！
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## Project layout
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## Hobby
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mkdocs.yml # The configuration file.
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docs/
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index.md # The documentation homepage.
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... # Other markdown pages, images and other files.
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outdoors, mountain climbing, on foot.
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I hope to complete my first snow mountain climb in 2025.
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<img src=".\assets\images\touxiang.png" style="zoom:40%;" />

‎docs/templates/main.html

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{% extends "base.html" %}
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{% block announce %}
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<center>
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You can follow <strong>@shenxiangzhuang</strong> on
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<a href="https://github.com/shenxiangzhuang">
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<span class="twemoji">
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{% include ".icons/fontawesome/brands/square-github.svg" %}
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</span>
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<strong>GitHub</strong>
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</a>
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or
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<strong>@MathewShen</strong> on
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<a href="https://twitter.com/MathewShen42">
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<span class="twemoji">
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{% include ".icons/fontawesome/brands/x-twitter.svg" %}
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</span>
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<strong>Twitter</strong>
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</a>
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and
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<a href="https://www.zhihu.com/people/shen-xiang-zhuang">
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<strong>知乎</strong>
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</a>
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or
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<strong>AI Glimpse</strong> on
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<!--暂时用 Why Beer 文章链接作为入口-->
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<a href="https://mp.weixin.qq.com/s/oq8viA9WFI87vUDtpNaV0Q">
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<span class="twemoji">
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{% include ".icons/fontawesome/brands/wechat.svg" %}
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</span>
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<strong>WeChat</strong>
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</a>
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</center>
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{% endblock %}
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{% block content %}
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{{ super() }}
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<!-- Giscus -->
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<script src="https://giscus.app/client.js"
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data-repo="shenxiangzhuang/shenxiangzhuang.github.io"
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data-repo-id="MDEwOlJlcG9zaXRvcnk4MjU0MjM1OQ=="
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data-category="Announcements"
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data-category-id="DIC_kwDOBOt_F84CTHBH"
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data-mapping="pathname"
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data-strict="0"
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data-reactions-enabled="1"
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data-emit-metadata="0"
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data-input-position="top"
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data-theme="light"
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data-lang="en"
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crossorigin="anonymous"
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async>
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</script>
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<!-- Synchronize Giscus theme with palette -->
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<script>
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var giscus = document.querySelector("script[src*=giscus]")
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/* Set palette on initial load */
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var palette = __md_get("__palette")
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if (palette && typeof palette.color === "object") {
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var theme = palette.color.scheme === "slate" ? "dark" : "light"
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giscus.setAttribute("data-theme", theme)
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}
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/* Register event handlers after documented loaded */
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document.addEventListener("DOMContentLoaded", function() {
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var ref = document.querySelector("[data-md-component=palette]")
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ref.addEventListener("change", function() {
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var palette = __md_get("__palette")
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if (palette && typeof palette.color === "object") {
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var theme = palette.color.scheme === "slate" ? "dark" : "light"
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/* Instruct Giscus to change theme */
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var frame = document.querySelector(".giscus-frame")
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frame.contentWindow.postMessage(
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{ giscus: { setConfig: { theme } } },
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"https://giscus.app"
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)
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</script>
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{% endblock %}

‎mkdocs.yml

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- navigation.indexes
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- search.suggest
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plugins:
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- autorefs
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- tags
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- search:
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# - minify:
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# - bibtex:

‎site/404.html

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<label class="md-header__button md-icon" for="__search">
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.516 6.516 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5Z"/></svg>
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<div class="md-search" data-md-component="search" role="dialog">
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<label class="md-search__overlay" for="__search"></label>
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<div class="md-search__inner" role="search">
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<form class="md-search__form" name="search">
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<input type="text" class="md-search__input" name="query" aria-label="Search" placeholder="Search" autocapitalize="off" autocorrect="off" autocomplete="off" spellcheck="false" data-md-component="search-query" required>
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.516 6.516 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5Z"/></svg>
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11h12Z"/></svg>
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M19 6.41 17.59 5 12 10.59 6.41 5 5 6.41 10.59 12 5 17.59 6.41 19 12 13.41 17.59 19 19 17.59 13.41 12 19 6.41Z"/></svg>
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Initializing search
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<script id="__config" type="application/json">{"base": "/", "features": ["navigation.tabs", "navigation.tabs.sticky", "navigation.top", "navigation.path", "navigation.instant", "navigation.indexes", "navigation.prune", "navigation.sections"], "search": "/assets/javascripts/workers/search.b8dbb3d2.min.js", "translations": {"clipboard.copied": "Copied to clipboard", "clipboard.copy": "Copy to clipboard", "search.result.more.one": "1 more on this page", "search.result.more.other": "# more on this page", "search.result.none": "No matching documents", "search.result.one": "1 matching document", "search.result.other": "# matching documents", "search.result.placeholder": "Type to start searching", "search.result.term.missing": "Missing", "select.version": "Select version"}}</script>
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<script id="__config" type="application/json">{"base": "/", "features": ["navigation.tabs", "navigation.tabs.sticky", "navigation.top", "navigation.path", "navigation.instant", "navigation.indexes", "navigation.prune", "navigation.sections", "search.suggest"], "search": "/assets/javascripts/workers/search.b8dbb3d2.min.js", "translations": {"clipboard.copied": "Copied to clipboard", "clipboard.copy": "Copy to clipboard", "search.result.more.one": "1 more on this page", "search.result.more.other": "# more on this page", "search.result.none": "No matching documents", "search.result.one": "1 matching document", "search.result.other": "# matching documents", "search.result.placeholder": "Type to start searching", "search.result.term.missing": "Missing", "select.version": "Select version"}}</script>
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