【Android 性能引擎】安装加速

提升App安装速度。

方案：把dex文件优化流程延迟处理。

效果：大型应用2-3s即可安装完毕。

影响：dex文件未处理完成前启动应用，会略微影响启动速度。多次连续安装App安装时间可能会变长。

关键代码：

PackageDexOptimizer#performDexOpt

@DexOptResult
    int performDexOpt(AndroidPackage pkg, @NonNull PackageStateInternal pkgSetting,
            String[] instructionSets, CompilerStats.PackageStats packageStats,
            PackageDexUsage.PackageUseInfo packageUseInfo, DexoptOptions options) {
        if (PLATFORM_PACKAGE_NAME.equals(pkg.getPackageName())) {
            throw new IllegalArgumentException("System server dexopting should be done via "
                    + " DexManager and PackageDexOptimizer#dexoptSystemServerPath");
        }
        if (pkg.getUid() == -1) {
            throw new IllegalArgumentException("Dexopt for " + pkg.getPackageName()
                    + " has invalid uid.");
        }
        if (!canOptimizePackage(pkg)) {
            return DEX_OPT_SKIPPED;
        }
        synchronized (mInstallLock) {
            final long acquireTime = acquireWakeLockLI(pkg.getUid());
            try {//此处可立即返回DEX_OPT_SKIPPED状态，并延迟处理performDexOptLI
                return performDexOptLI(pkg, pkgSetting, instructionSets,
                        packageStats, packageUseInfo, options);
            } finally {
                releaseWakeLockLI(acquireTime);
            }
        }
    }

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