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| <div id="app" data-server-rendered="true"><div class="theme-container vuepress-theme-fast"><header class="navbar"><div class="sidebar-button"><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" role="img" viewBox="0 0 448 512" class="icon"><path fill="currentColor" d="M436 124H12c-6.627 0-12-5.373-12-12V80c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12zm0 160H12c-6.627 0-12-5.373-12-12v-32c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12zm0 160H12c-6.627 0-12-5.373-12-12v-32c0-6.627 5.373-12 12-12h424c6.627 0 12 5.373 12 12v32c0 6.627-5.373 12-12 12z"></path></svg></div><a href="/zh/" class="home-link router-link-active"><img src="/logo@2x.svg" alt="WEEX" class="logo"></a><span class="version"><a href="/download/download.html" class="version-bg"><img src="/assets/img/version-bg.ab65ded9.svg" alt="v0.28"><span class="version-no">v0.28</span></a></span><div class="links"><form id="search-form" class="algolia-search-wrapper search-box"><input id="algolia-search-input" class="search-query"></form><nav class="nav-links can-hide"><div class="nav-item"><a href="/zh/guide/" class="nav-link">指南</a></div><div class="nav-item"><a href="/zh/docs/" class="nav-link">文档</a></div><div class="nav-item"><a href="/zh/tools/" class="nav-link">第三方工具</a></div><div class="nav-item"><a href="/zh/download/" class="nav-link">下载</a></div><div class="nav-item"><a href="/zh/community/" class="nav-link">社区</a></div><div class="nav-item"><a href="/zh/blog/" class="nav-link router-link-active">博客</a></div><div class="nav-item"><div class="dropdown-wrapper"><a class="dropdown-title"><span class="title">选择语言</span><span class="arrow right"></span></a><ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----><a href="/" class="nav-link">English</a></li><li class="dropdown-item"><!----><a href="/zh/blog/weexcore-multiprocess-evolution.html" class="nav-link router-link-exact-active router-link-active">简体中文</a></li></ul></div></div></nav><a href="https://github.com/apache/incubator-weex" target="_blank" rel="noopener noreferrer" class="repo-link"><img src="/assets/img/github.7cb484a9.svg" alt="github" class="github-icon"></a></div></header><div class="sidebar-mask"></div><div class="sidebar"><nav class="nav-links"><div class="nav-item"><a href="/zh/guide/" class="nav-link">指南</a></div><div class="nav-item"><a href="/zh/docs/" class="nav-link">文档</a></div><div class="nav-item"><a href="/zh/tools/" class="nav-link">第三方工具</a></div><div class="nav-item"><a href="/zh/download/" class="nav-link">下载</a></div><div class="nav-item"><a href="/zh/community/" class="nav-link">社区</a></div><div class="nav-item"><a href="/zh/blog/" class="nav-link router-link-active">博客</a></div><div class="nav-item"><div class="dropdown-wrapper"><a class="dropdown-title"><span class="title">选择语言</span><span class="arrow right"></span></a><ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----><a href="/" class="nav-link">English</a></li><li class="dropdown-item"><!----><a href="/zh/blog/weexcore-multiprocess-evolution.html" class="nav-link router-link-exact-active router-link-active">简体中文</a></li></ul></div></div></nav><ul class="sidebar-links"><li><a href="/zh/blog/write-a-blog.html" class="sidebar-link">写一篇博客</a></li><li><a href="/zh/blog/weex-auto-test-locating.html" class="sidebar-link">Weex自动化测试元素定位方案</a></li><li><a href="/zh/blog/ios-weexcore.html" class="sidebar-link">iOS WeexSDK 接入 WeexCore</a></li><li><a href="/zh/blog/weexcore-multiprocess-evolution.html" class="active sidebar-link">WeexCore 多进程多线程架构演进</a><ul class="sidebar-sub-headers"></ul></li><li><a href="/zh/blog/interaction-optimization.html" class="sidebar-link">可交互时间的探索和首屏时间的改进之路</a></li><li><a href="/zh/blog/what_is_the_most_important_assest_to_an_open_souce_project.html" class="sidebar-link">什么是一个开源项目最重要的资产？</a></li><li><a href="/zh/blog/weex-third-party-extensions.html" class="sidebar-link">Weex 三方插件</a></li></ul></div><div class="page"><div class="content"><h1 id="weexcore-多进程多线程架构演进"><a href="#weexcore-多进程多线程架构演进" class="header-anchor">#</a> WeexCore 多进程多线程架构演进</h1><h3 id="_1-背景"><a href="#_1-背景" class="header-anchor">#</a> 1. 背景</h3><p><code>Weex Android</code> 早在 2016 年时就采用了多线程的模型来提升 <code>Weex</code> 的渲染能力. <code>DomThread</code>, <code>JSThread</code>, <code>UIThread</code> . 去年双十一 <code>Weex</code> 进化成多进程模式来提升 <code>Weex</code> 的稳定性. 所以理论上来说, Weex 早就是多进程多线程的模式了, 为什么现在还在谈这个事情. 且听我慢慢重新介绍一些目前的 <code>WeexCore</code></p><p><code>WeexCore</code> 在今年三月份的时候, 加入了一个新的成员, 叫 <code>LayoutEngine</code>, 它的算法都沉到 c++ 层. 而且一同带下来的还有它的合作伙伴 <code>Parser</code>. 这样, <code>DOM 解析</code>和 <code>Layout</code> 全家桶就全部进入了 <code>JSThread</code>. 在减少一个线程的情况下, Weex 的渲染性能还能有所提升, 足以说明目前的 <code>LayoutEngine</code> 的强大.</p><p>演变过程大致如下图所示, 黄色 DOMParser 本来在一个独立的线程里, 现在和绿色块合成了一个线程. |
| <img src="/blog/weexcore-multiprocess-evolution/f31103153fd160ae4723069f88c61e34.png" alt="2018-12-07 at 13.18.png"></p><p>再说说多进程, Weex 的 jsEngine 从 V8 切到了 JavaScriptCore. 但由于以下几个问题, 所以将 JSC 引擎放到了子进程里运行.</p><ol><li>在JSC引擎上线出现许多无定位的稳定性问题，威胁手淘等使用Weex的客户端的稳定性。</li><li>JSC容易耗TLS（Thread Local Storage），导致TLS slot耗尽，易引起其他模块的崩溃。</li><li>JSC引擎性能虽好，但是占用内存较大，在低端机容易引起内存吃紧，导致手淘进程被杀。</li></ol><p>这套多进程架构在当时来看是非常完美的, 采用多进程模型切到 jscEngine, 既提升了渲染能力, 也提升了 Weex 的整体稳定性.</p><p>但这种模型在某些方面还是存在不足, 例如虽然是多进程, 但实际上还是单线程的运作模式, 且子进程无法主动向主进程发送消息. 而且 Native 定时器也无法友好的实现.</p><p>先说说为什么多进程下, 为什么还是单线程的模型.</p><p><img src="/blog/weexcore-multiprocess-evolution/872298694d6e7f1a311ade626da0f0f8.png" alt="2018-12-07 at 11.29.png"></p><p>如上图所示, 一块共享内存分为16份, 父进程(WeexCore) 写偶数块, 读奇数块. 子进程(JSS) 写奇数块, 读偶数块.</p><p>初始化时, 父进程锁住 0 内存块. 子进程锁住 1 内存块, 子进程启动监听, 请求锁 0 内存块. 但此时 0 内存块被父进程锁着, 所以子进程请求锁 0 内存块失败, wait 父进程释放 0 内存块. 就这样, 两个进程因为互相竞争一块共享内存, 所以变相的成为单线程模式. 既同一时间只有一个进程能够保持活跃状态.</p><p>这意味着当前模型下, <strong>Weex 所有的操作入口只能是 Platform 层, 子进程只能响应父进程的任务, 不能主动的执行某个任务, 且父进程在执行 Layout 或 parser 操作时, JSEngine 是处于挂起的状态的.</strong></p><p>所以, WeexCore 的线程模型演变成下面这个样子.</p><p><img src="/blog/weexcore-multiprocess-evolution/cc6710bafd8edd87a577c72d89a764fb.png" alt="2018-12-07 at 12.23.png"></p><p>从架构上来说, 主要有以下几个变动</p><ul><li><ol><li>WeexCore 演变成消息驱动的线程异步交互模型.</li></ol></li></ul><ul><li>新增 I/O Thread 来拓展原有单向的 IPC, 使子进程可主动的向父进程发送消息. I/O Thread 只用来任务转发, 相比之前还需 wait 任务执行完毕, 效率提升非常明显.</li><li>新增 JS Thread 来专门的执行 js 任务. 不再受上层 Layout 和 Parser 任务的阻塞.</li><li>针对 NativeTimer 新增一个 Timer 线程来做定时器计算, 这个后面会具体讲到.</li></ul><ul><li><ol start="2"><li>WeexCore 分层设计. IPC 可热插拔的自由切换</li></ol></li></ul><h3 id="_2-详解"><a href="#_2-详解" class="header-anchor">#</a> 2. 详解</h3><h4 id="_2-1-消息驱动的异步通信模型"><a href="#_2-1-消息驱动的异步通信模型" class="header-anchor">#</a> 2.1. 消息驱动的异步通信模型</h4><p>线程的异步通信模型可以避免线程间互不阻塞，提⾼高线程的并发性 |
| <img src="/blog/weexcore-multiprocess-evolution/937def357b6528b0d78f0e948560e5dc.png" alt="2018-12-07 at 12.36.png"></p><p>异步通信可以通过简单的控制线程共享的 volatile 变量或者信号量 mutex 和条件异步调⽤用到其他线程 的函数块，然⽽简单粗暴的使⽤用这些⽅式时，线程的边界会变得不明显或者代码块都充斥着锁和信号量的控制，如果数据需要线程公用，还需要对数据块上锁，导致死锁或异步能⼒下降，对本身代码的维护和程序的稳定性都有影响。 |
| 消息驱动的异步通信模型结是常用的线程循环模型，是一种非侵⼊式设计，消息结构耦合度底，线程中的循环实现灵活度高。尽管它也是基于上述的⽅式去进⾏线程切换，但相⽐起直接对⽅法⽤锁，或者直接利用 volatile，通过消息使代码块和数据边界明显，提⾼了程序的线程安全性，线程间互不阻塞，提⾼线程的并发性。它代表着⼀种设计哲学，但是这并不是代表它没有任何锁控制，只是可以把锁限制在⼀个极⼩的范围内。 |
| 技术要点</p><ol><li>跨平台、⾼高效、易易⽤用的消息驱动的异步通信模型。</li><li>能适应当前 Weex 的线程模型——不不改变上层 Platform 层的线程模型，WeexCore 能兼容上层 |
| 的消息循环机制，例例如 Android Handler。</li></ol><h5 id="_2-1-1-总体设计"><a href="#_2-1-1-总体设计" class="header-anchor">#</a> 2.1.1 总体设计</h5><p><img src="/blog/weexcore-multiprocess-evolution/4545bcabcdac57acfe0be1692a8b9cc5.png" alt="2018-12-07 at 12.40.png"></p><p>上图是消息驱动框架的简要类关系图，整体的流程是创建或者依附到 Thread 环境，通过消息泵 MessagePump 完成线程切换，驱动消息循环体 MessageLoop 进⾏消息循环，在当前线程中执⾏来自于其他线程丢进池⼦中的消息。</p><ul><li>Thread ⽤用于构建当前线程环境，当模式是依附到 Android 或 iOS 的线程时，Thread 是⼀一个⽤用 来装载 MessageLoop 的壳⼦，不会新构建任何线程环境。</li><li>MessageLoop 是真正进⾏消息执⾏和存储的对象。它实现了 MessagePump::Delegate 的接⼝，表示它能接受来⾃消息泵的驱动</li><li>MessagePump 是⼀个消息泵，即驱动器，负责及时或定时切换线程环境，驱动消息循环，完成 消息从⼀个线程传递到另⼀个线程的执⾏的过程</li></ul><h5 id="_2-1-2-具体流程"><a href="#_2-1-2-具体流程" class="header-anchor">#</a> 2.1.2 具体流程</h5><p>下⾯将从 Thread 创建过程中相关对象的创建流程图、消息循环初始化流程图和消息驱动流程图上分 析，通过具体流程可以了解内部对跨平台和对当前 Weex 的上层线程模型的适配机制。</p><p><img src="/blog/weexcore-multiprocess-evolution/7d0c65a3a4b79ac3d990dfaa8f203be1.png" alt="2018-12-07 at 12.42.png"></p><p>上图是 Thread 创建过程中相关对象的创建流程图。当外界通过 new 创建 Thread 时，需要带上 MessageLoop::Type 的参数（关键：⽤于创建 MessagePump，启动时会根据类型判断是否要创建线 程环境）。ThreadImpl 是 Thread 的实现类，是真正⽤于创建 Thread 环境的对象，它是⼀个抽象类，它的⼦类后缀分别是 Android / iOS / Posix。这些⼦类分别代表了各个环境下的实现。Android 和 iOS 都是 Unix-like 系统，因此他们使⽤的都是 Posix 线程，但是在 pthread 的操作上会有不⼀致 的地⽅，例如 pthread_setname_np 在 Android 和 iOS 上传递的参数不⼀样。因此根据不同系统去 对应的对实现类做出调整。Thread 在初始化 Impl 时会根据宏定义确定初始化的 Impl ⼦类，从⽽做到平台适应。</p><p>ThreadImpl 持有⼀个维护消息队列的 MessageLoop，再初始化时也会⼀并创建。MessageLoop 中 持有⼀个驱动器 MessagePump，MessagePump 是⼀个接⼝类，具体实现类由 MessageLoop::Type 决定。MessageLoop::Type 具有两种类型，DEFAULT 指驱动器由默认的 Posix Thread ⽅式进⾏，PLATFORM 指驱动器由兼容 Android 或 iOS 的线程环境和消息循环⽅式实现（具体循环请继续向后）。</p><p><img src="/blog/weexcore-multiprocess-evolution/950b476fb53468ba2f309b73435a9e15.png" alt="2018-12-07 at 12.43.png"></p><p>上图是消息循环初始化流程图。当 Thread 创建完成后，需要通过 Thread::Start ⽅法完成内部消息循 环的构建流程。Thread::Start ⽅法会通过实现类 ThreadImpl::Run 完成，ThreadImplPosix 是 Android / iOS 的基类，基类中 Run ⽅法会对 MessageLoop::Type 进⾏判断：</p><ul><li>如果是 PLATFORM ⽆需创建新的线程环境，⽽是直接依附到当前线程，紧接着调⽤ MessageLoop::Run</li><li>如果是 DEFAULT 类型，则需要通过 pthread_create 初始化线程环境，并在新线程中执⾏ MessageLoop::Run。这⾥有⼀个⼩点，为了确保外部执⾏完 Start 后可以执⾏抛消息操作 ，当 前线程会通过 WaitableEvent 同步等待新线程完成初始化。</li></ul><p>MessageLoop 在这⾥的作⽤只是⽤于执⾏消息和存储消息，因此 MessageLoop::Run 并不会进⼊⽆ 限循环，它将这个动作交由驱动器 MessagePump 决定是进⼊⽆限循环还是依附上层。</p><ul><li>在 MessagePumpPosix 情况下，必然是⼀个不依附与上层的新线程，整体的循环由⾃⼰把控， Run ⽅法内部通过信号量 mutex 和条件 condition 进⼊等待消息状态。</li><li>在 MessagePumpAndroid 情况下，Run ⽅法内部主要通过 jni ⽅法创建和绑定 java 层 SystemMessageHandler 对象，建⽴和上层 Android 消息循环机制的关联。</li><li>在 MessagePumpDarwin 情况下，Run ⽅法内部通过获取当前线程的 CFRunLoopRef 和创建 CFRunLoopSourceRef 对象，建⽴和上层 iOS 消息循环机制的关联。</li></ul><p>到此消息循环的初始化流程完成，DEFAULT 类型进⼊了线程阻塞等待唤醒，⽽ PLATFORM 类型进⼊ 了等待来⾃ Android / iOS 的调度。</p><p><img src="/blog/weexcore-multiprocess-evolution/965358b8880bc1e1547654ca3f26b79a.png" alt="2018-12-07 at 12.45.png"></p><p>上图是消息驱动流程图。当外界在其他线程通过指定线程的 MessageLoop 进⾏ PostTask 传进来了⼀ 个任务 closure，内部会对 DelayedTaskQueue 上锁，确保安全的添加操作，此时 closure 会变成 DelayedTask 扔进池⼦⾥，释放锁。通知消息泵有消息进来：</p><ul><li>如果是 MessagePumpPosix，将会通过 condiion::notify_one 唤醒对应线程，对应线程将进⼊ MessageLoop::DoWork</li><li>如果是 MessagePumpAndroid，将会通过 jni 到上层 SystemMessageHandler 的 scheduleWork ，向 Android handler 抛消息，切换到对应线程，再回调到底层的 MessageLoop::DoWork</li><li>如果是 MessagePumpDarwin，将对 CFRunLoopSourceRef 对象标记待处理，再通过 CFRunLoopWakeUp 唤醒线程，切换到对应线程，再回调到底层的 MessageLoop::DoWork</li></ul><p>MessageLoop::DoWork 中⾸先对 DelayedTaskQueue 上锁，通过对⽐ DelayedTask 时间和当前时 间获取需要执⾏的 closure 列表，如果还有任务，则通知消息泵定时驱动，接着释放锁，执⾏ closure 列表。结束后如果是 MessagePumpPosix，则需阻塞当前线程，等待下次唤醒。</p><h5 id="_2-1-3-closure-设计"><a href="#_2-1-3-closure-设计" class="header-anchor">#</a> 2.1.3 closure 设计</h5><p><img src="/blog/weexcore-multiprocess-evolution/1b94848aaa731b146228090093b5cc92.png" alt="2018-12-07 at 12.47.png"></p><p>closure 是⼀个任务的载体，它实际是⼀个 std::function。它在被扔进任务池⼦⾥⾯时，它的⽣命周 期就跟随着线程，除⾮它离开了执⾏队列被执⾏，那么它的⽣命周期将在执⾏后被销毁，否则未被执 ⾏的任务将在执⾏完后⾃动析构。⽽这个可以拷⻉的 function 是通过 CopyableLambda 实现的， CopyableLambda 通过创建⼀个指向数据的共享指针，然后创建⼀个可复制的 lambda 来捕获该共享 指针，然后将该可复制的 lambda 包装成 std::function 请求的签名，赋予 std::function 函数拷⻉的 功能，可供 MessageLoop 持有调度。</p><p>由于涉及了跨线程传递参数对象，因此参数对象尤其是指针的⽣命周期管理需要异常⼩⼼。 std::function ⽀持使⽤ lambda 表达式，在 lambda 表达式中要善⽤智能指针，确保指针的⽣命周期 在 task 结束仍然有效，例如使⽤ unique_ptr 将指针的⽣命周期转移交给 task。</p><h5 id="_2-1-4-使⽤姿势"><a href="#_2-1-4-使⽤姿势" class="header-anchor">#</a> 2.1.4 使⽤姿势</h5><p>以 WeexCore 的例⼦为例，当 JSS 从 IO 线程向 WeexCore 发送了 CallNative 的指令，那么在 WeexCore 中回到 JS 线程的⽅式是：</p><div class="language-c++ extra-class"><pre class="language-text"><code>WeexCoreManager::Instance()->script_thread()->message_loop()->PostTask( |
| weex::base::MakeCopyable([page_id = std::string(page_id), task = std::string(task), callback = std::string(callback)] { |
| |
| // CallNative |
| |
| })); |
| </code></pre></div><h4 id="_2-2-weexcore-分层设计"><a href="#_2-2-weexcore-分层设计" class="header-anchor">#</a> 2.2. WeexCore 分层设计</h4><p>IPC 可热插拔, 单双进程自由切换</p><p><img src="/blog/weexcore-multiprocess-evolution/22195f7e61b2267f50dc78226d98aff3.png" alt="2018-12-07 at 13.05.png"></p><p>如图所示.</p><p>Weex 目前整体可以分为三层</p><ol><li>Platform(Android, iOS, ..)</li><li>WeexCore(Layout, Parser)</li><li>JSS(JSEngine 子进程).</li></ol><p>我们在每个层面之间加入了一个 Bridge, 每个 Bridge 对应两个 Side. 每个 Side 对应三种模式</p><ol><li>Multi Process: 多进程模式, 通过IPC 通信.</li><li>Multi So: 多 So 模式, 通过函数指针互相调用.</li><li>Simple: 内部模式, 可以互相调用.</li></ol><p>例如目前 Weex 的多进程模式是 PlatformBridge 对应的Side 为 Simple, ScriptBridge 的 side 都是 MultiProcess.</p><p>如果 IPC 上移, 或者切换单进程不使用 IPC, 只需要切对应的 Side 即可.</p><h3 id="_3-效果"><a href="#_3-效果" class="header-anchor">#</a> 3. 效果</h3><p>多线程架构完成之时, 测试同学进行了一次完整的性能测试, 在复杂的页面下,性能提升比较明显, 多线程架构上线之后, 通过线上埋点观察到性能也有了不小的提升.</p><p>多线程架构给 Weex 带来的不仅仅是性能上的提升, 个人认为高拓展性才是最大的收益. |
| 例如 NativeTimer 和未来即将做的 Native DomAPI 在老的架构下是无法做出来的.</p><p>目前 Weex 的很多逻辑都沉入了 c 层, JSFramework 的能力也上浮到客户端来做, |
| 不久的将来 WeexCore 将做到平台无关, JSFramework 全 Native 化, 欢迎有兴趣的同学一起来共建 WeexCore.</p></div><div class="page-nav"><p class="inner"><span class="prev"> |
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