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BoostMultiDex是一个用于Android低版本设备(4.X及以下,SDK < 21)快速加载多DEX的解决方案,由抖音/Tiktok Android技术团队出品。

相比于Android官方原始MultiDex方案,它能够减少80%以上的黑屏等待时间,挽救低版本Android用户的升级安装体验。并且,不同于目前业界所有优化方案,BoostMultiDex方案是从Android Dalvik虚拟机底层机制入手,从根本上解决了安装APK后首次执行MultiDex耗时过长问题。

背景

我们知道,Android低版本(4.X及以下,SDK < 21)的设备,采用的Java运行环境是Dalvik虚拟机。它相比于高版本,最大的问题就是在安装或者升级更新之后,首次冷启动的耗时漫长。这常常需要花费几十秒甚至几分钟,用户不得不面对一片黑屏,熬过这段时间才能正常使用APP。

这是非常影响用户的使用体验的。尤其在海外,像东南亚以及拉美等地区,还存有着很大量的低端机。4.X以下低版本用户虽然比较少,但对于抖音及Tiktok这样有着亿级规模的用户的APP,即使占比10%,数目也有上千万。因此如果想要打通下沉市场,这部分用户的使用和升级体验是绝对无法忽视的。

这个问题的根本原因就在于,安装或者升级后首次MultiDex花费的时间过于漫长。为了解决这个问题,我们挖掘了Dalvik虚拟机的底层系统机制,对DEX相关处理逻辑进行了重新设计,最终推出了BoostMultiDex方案,挽救低版本Android用户的升级安装体验。

技术要点

BoostMultiDex方案的技术实现要点如下:

  1. 利用系统隐藏函数,直接加载原始DEX字节码,避免ODEX耗时
  2. 多级加载,在DEX字节码、DEX文件、ODEX文件中选取最合适的产物启动APP
  3. 单独进程做OPT,并实现合理的中断及恢复机制

更重要的是,BoostMultiDex已经在抖音/TikTok亿级全球用户上验证通过,可以说涵盖了各个国家、各种复杂情况的Android机型,目前业界其他大型APP都很难涉及到如此广泛的规模。由此,我们也解决了各种奇怪的兼容性问题,最大程度上确保了技术方案的稳定性。

快速接入

build.gradle的dependencies中添加依赖:

dependencies {
... ...
    // For specific version number, please refer to app demo
    implementation 'com.bytedance.boost_multidex:boost_multidex:${ARTIFACT_VERSION}'
}

与官方MultiDex类似,在Application.attachBaseContext的最前面进行初始化即可:

public class YourApplication extends Application {

    @Override
    protected void attachBaseContext(Context base) {
        super.attachBaseContext(base);
        
        BoostMultiDex.install(base);
        
... ...
    }

编译构建

如果想自行编译打包,需要使用R16B版本的NDK以支持armeabi架构,如果不需要,可以直接在boost_multidex/build.gradle中去掉此依赖。

执行以下命令即可构建本地aar包:

./gradlew :boost_multidex:assembleRelease

产物为boost_multidex/build/outputs/aar/boost_multidex-release.aar

性能对比

Android版本 厂商 机型 原始MultiDex耗时(s) BoostMultiDex耗时(s)
4.4.2 LG LGMS323 33.545 5.014
4.4.4 MOTO G 45.691 6.719
4.3 Samsung GT-N7100 24.186 3.660
4.3.0 Samsung SGH-T999 30.331 3.791
4.2.2 HUAWEI Hol-T00 崩溃 3.724
4.2.1 HUAWEI G610-U00 36.465 4.981
4.1.2 Samsung I9100 30.962 5.345

以上是在抖音上测得的实际数据,APK中共有6个Secondary DEX,显而易见,BoostMultiDex方案相比官方MultiDex方案,其耗时有着本质上的优化,基本都只到原先的11%~17%之间。 也就是说BoostMultiDex减少了原先过程80%以上的耗时。 另外我们看到,其中有一个机型,在官方MultiDex下是直接崩溃,无法启动的。使用BoostMultiDex也将使得这些机型可以焕发新生。

详细原理

请参考本项目Wiki

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BoostMultiDex is a solution for quickly loading multiple dex files on low Android version devices (4.X and below, SDK <21). 展开 收起
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