ActivityThread：
它管理 应用步调进程 中主线程的实验，调理和实验Activity，广播，
以及ActivityManager 哀求的其他操纵。
简朴的说，可以通过这个类，获取到当前应用的一些信息
TIPS:
(1).可以使用以下的开源代码网站检察源码
http://aosp.opersys.com/xref/android-12.0.0_r2/xref/frameworks/base/core/java/android/app/ActivityThread.java
(2).也可以通过AndroidStudio 下载SDK Source code 检察
1 代码目次分析
它在源码的目次是在framework下： /frameworks/base/core/java/android/app/
包名为 android.app;
但它有 @hide 标记，则在app无法直接访问，但是可以通过反射获取(如Hook 技能中常用)
package android.app;/** * This manages the execution of the main thread in an * application process, scheduling and executing activities, * broadcasts, and other operations on it as the activity * manager requests. * * {@hide} */public final class ActivityThread extends ClientTransactionHandler implements ActivityThreadInternal {2. 获取当前应用 currentApplication()
Application application = ActivityThread.currentApplication();即可以获取到当前代码运行到的地方，它所属的 应用.
application.mLoadedApk 直接获取到当前 加载的应用对象
3. 获取当前 已加载的应用(LoadedApk) 对象 (getPackageInfo())
3. 1 资源目次成员变量 mResourcePackages
是一个map, 表现1个大概多个路径.
同时，相当于一个缓存， 后续纵然App 更改了 LoadedApk里的内容，但是在这里生存的对象大概是稳定的.
@GuardedBy("mResourcesManager") @UnsupportedAppUsage final ArrayMap<String, WeakReference<LoadedApk>> mResourcePackages = new ArrayMap<>();PS: 尚有别的一个变量mPackages是生存 代码所在的目次
@GuardedBy("mResourcesManager")
@UnsupportedAppUsage
final ArrayMap<String, WeakReference<LoadedApk>> mPackages = new ArrayMap<>();
3. 2 public 方法
在通过API getPackageInfo 获取 LoadedApk ，由几个public 的方法，参数差别处置惩罚流程略有差别.
都是不公开的，@UnsupportedAppUsage
public final LoadedApk getPackageInfo(ApplicationInfo ai, CompatibilityInfo compatInfo, int flags) {} public final LoadedApk getPackageInfo(String packageName, CompatibilityInfo compatInfo, int flags) {} public final LoadedApk getPackageInfo(String packageName, CompatibilityInfo compatInfo, int flags, int userId) { public final LoadedApk getPackageInfoNoCheck(ApplicationInfo ai, CompatibilityInfo compatInfo) {} 3. 3 private 实现方法
内部的私有方法， 会根据packageName 查询 mResourcePackages 实验获取 LoadedApk 对象
假如不存在，大概会创建并生存(当进步程 和 传入的 appinfo 的userId差别时除外!!!)
判定userId的关键代码：
final boolean differentUser = (UserHandle.myUserId() != UserHandle.getUserId(aInfo.uid));重点在于是从哪个进程调用这个方法的， 即UserHandle.myUserId() 的值取决于 !!调用者!! 的进程
私有API(1) 仅仅是获取：
private LoadedApk getPackageInfo(ApplicationInfo aInfo, CompatibilityInfo compatInfo, ClassLoader baseLoader, boolean securityViolation, boolean includeCode, boolean registerPackage, boolean isSdkSandbox, boolean isCallFromReceiver) { /* APK_OPTIMIZATION } */ final boolean differentUser = (UserHandle.myUserId() != UserHandle.getUserId(aInfo.uid)); synchronized (mResourcesManager) { WeakReference<LoadedApk> ref; if (differentUser || isSdkSandbox) { // Caching not supported across users and for sdk sandboxes ref = null; } else if (includeCode) { ref = mPackages.get(aInfo.packageName); } else { ref = mResourcePackages.get(aInfo.packageName); } 私有方法API(2)： 会举行创建 LoadedApk 并缓存起来 ()
假如缓存中没有，则会根据传入的 appInfo 创建一个新的 loadedApk 对象。
当进步程 和 appInfo是同个用户的话， 生存到mResourcePackages
2485 private LoadedApk getPackageInfo(ApplicationInfo aInfo, CompatibilityInfo compatInfo,2486 ClassLoader baseLoader, boolean securityViolation, boolean includeCode,2487 boolean registerPackage) {2488 final boolean differentUser = (UserHandle.myUserId() != UserHandle.getUserId(aInfo.uid));2489 synchronized (mResourcesManager) {2490 WeakReference<LoadedApk> ref;2491 if (differentUser) { ////>>>>>>>>>>>>>>>>>> 查抄用户userId2492 // Caching not supported across users2493 ref = null;2494 } else if (includeCode) {2495 ref = mPackages.get(aInfo.packageName);2496 } else {2497 ref = mResourcePackages.get(aInfo.packageName);2498 }24992500 LoadedApk packageInfo = ref != null ? ref.get() : null;25012502 if (packageInfo != null) {2503 if (!isLoadedApkResourceDirsUpToDate(packageInfo, aInfo)) {2504 List<String> oldPaths = new ArrayList<>();2505 LoadedApk.makePaths(this, aInfo, oldPaths);2506 packageInfo.updateApplicationInfo(aInfo, oldPaths);2507 }25082509 return packageInfo; //////>>>>>>>>>>>>>>>>>> 非空则返回2510 }25112512 if (localLOGV) {2513 Slog.v(TAG, (includeCode ? "Loading code package "2514 : "Loading resource-only package ") + aInfo.packageName2515 + " (in " + (mBoundApplication != null2516 ? mBoundApplication.processName : null)2517 + ")");2518 }25192520 packageInfo =2521 new LoadedApk(this, aInfo, compatInfo, baseLoader,2522 securityViolation, includeCode2523 && (aInfo.flags & ApplicationInfo.FLAG_HAS_CODE) != 0, registerPackage); //////>>创建新的25242525 if (mSystemThread && "android".equals(aInfo.packageName)) {2526 packageInfo.installSystemApplicationInfo(aInfo,2527 getSystemContext().mPackageInfo.getClassLoader());2528 }25292530 if (differentUser) {2531 // Caching not supported across users2532 } else if (includeCode) {2533 mPackages.put(aInfo.packageName,2534 new WeakReference<LoadedApk>(packageInfo));2535 } else {2536 mResourcePackages.put(aInfo.packageName,2537 new WeakReference<LoadedApk>(packageInfo));//////>>做缓存2538 }25392540 return packageInfo;2541 }2542 }3.4 调用 ActivityThread.getPackageInfo() 的地方：
（1） 通过 ApplicationInfo 创建 Context的时候
Context.createApplicationContext(mApplication, Context.CONTEXT_RESTRICTED);
---> ContextWrapper -> ContextImpl
此中 mApplication 为ApplicationInfo 对象.
//ContextImpl.java @Override public Context createApplicationContext(ApplicationInfo application, int flags) throws NameNotFoundException { LoadedApk pi = mMainThread.getPackageInfo(application, mResources.getCompatibilityInfo(), flags | CONTEXT_REGISTER_PACKAGE); if (pi != null) { ContextImpl c = new ContextImpl(this, mMainThread, pi, ContextParams.EMPTY, mAttributionSource.getAttributionTag(), mAttributionSource.getNext(), null, mToken, new UserHandle(UserHandle.getUserId(application.uid)), flags, null, null); final int displayId = getDisplayId(); final Integer overrideDisplayId = mForceDisplayOverrideInResources ? displayId : null; c.setResources(createResources(mToken, pi, null, overrideDisplayId, null, getDisplayAdjustments(displayId).getCompatibilityInfo(), null)); if (c.mResources != null) { return c; } } throw new PackageManager.NameNotFoundException( "Application package " + application.packageName + " not found"); }从上面可以看出，会先通过 ActivityThread.getPackageInfo 获取到 LoadedApk 实例对象.
3.5 拓展
ContextImpl 有几个通过差别参数，获取Context 的方法：
这里关注的是createApplicationContext 和 createPackageContextAsUser，
紧张差别在于前者传入 applicationInfo ，而后者是 packageName。
以是，差别会提如今 ActivityThread.getPackageInfo 获取 LoadedApk 对象上，
在根据 packageName查找缓存数组mResourcePackage， 后
假如不存在，前者会根据 applicationInfo 创建对象loadedApk对象, 后者则是通过packageName获取applicationInfo再创建.
//ContextImpl.java 获取Context 的几个方法 @Override public Context createApplicationContext(ApplicationInfo application, int flags) throws NameNotFoundException { LoadedApk pi = mMainThread.getPackageInfo(application, mResources.getCompatibilityInfo(), flags | CONTEXT_REGISTER_PACKAGE); if (pi != null) { ContextImpl c = new ContextImpl(this, mMainThread, pi, ContextParams.EMPTY, mAttributionSource.getAttributionTag(), mAttributionSource.getNext(), null, mToken, new UserHandle(UserHandle.getUserId(application.uid)), flags, null, null); final int displayId = getDisplayId(); final Integer overrideDisplayId = mForceDisplayOverrideInResources ? displayId : null; c.setResources(createResources(mToken, pi, null, overrideDisplayId, null, getDisplayAdjustments(displayId).getCompatibilityInfo(), null)); if (c.mResources != null) { return c; } } throw new PackageManager.NameNotFoundException( "Application package " + application.packageName + " not found"); } @Override public Context createPackageContext(String packageName, int flags) throws NameNotFoundException { return createPackageContextAsUser(packageName, flags, mUser); } @Override public Context createPackageContextAsUser(String packageName, int flags, UserHandle user) throws NameNotFoundException { if (packageName.equals("system") || packageName.equals("android")) { // The system resources are loaded in every application, so we can safely copy // the context without reloading Resources. return new ContextImpl(this, mMainThread, mPackageInfo, mParams, mAttributionSource.getAttributionTag(), mAttributionSource.getNext(), null, mToken, user, flags, null, null); } LoadedApk pi = mMainThread.getPackageInfo(packageName, mResources.getCompatibilityInfo(), flags | CONTEXT_REGISTER_PACKAGE, user.getIdentifier()); if (pi != null) { ContextImpl c = new ContextImpl(this, mMainThread, pi, mParams, mAttributionSource.getAttributionTag(), mAttributionSource.getNext(), null, mToken, user, flags, null, null); final int displayId = getDisplayId(); final Integer overrideDisplayId = mForceDisplayOverrideInResources ? displayId : null; c.setResources(createResources(mToken, pi, null, overrideDisplayId, null, getDisplayAdjustments(displayId).getCompatibilityInfo(), null)); if (c.mResources != null) { return c; } } // Should be a better exception. throw new PackageManager.NameNotFoundException( "Application package " + packageName + " not found"); } @Override public Context createContextAsUser(UserHandle user, @CreatePackageOptions int flags) { try { return createPackageContextAsUser(getPackageName(), flags, user); } catch (NameNotFoundException e) { throw new IllegalStateException("Own package not found: package=" + getPackageName()); } }createPackageContextAsUser 涉及在ActivityThread获取applicationInfo 的逻辑如下
（终极照旧回归到 包罗applicationInfo参数 的 getPackageInfo方法）
@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P, trackingBug = 115609023) public final LoadedApk getPackageInfo(String packageName, CompatibilityInfo compatInfo, int flags) { return getPackageInfo(packageName, compatInfo, flags, UserHandle.myUserId()); } public final LoadedApk getPackageInfo(String packageName, CompatibilityInfo compatInfo, int flags, int userId) { final boolean differentUser = (UserHandle.myUserId() != userId); ApplicationInfo ai = PackageManager.getApplicationInfoAsUserCached( packageName, PackageManager.GET_SHARED_LIBRARY_FILES | PackageManager.MATCH_DEBUG_TRIAGED_MISSING, (userId < 0) ? UserHandle.myUserId() : userId); synchronized (mResourcesManager) { WeakReference<LoadedApk> ref; if (differentUser) { // Caching not supported across users ref = null; } else if ((flags & Context.CONTEXT_INCLUDE_CODE) != 0) { ref = mPackages.get(packageName); } else { ref = mResourcePackages.get(packageName); } LoadedApk packageInfo = ref != null ? ref.get() : null; if (ai != null && packageInfo != null) { if (!isLoadedApkResourceDirsUpToDate(packageInfo, ai)) { List<String> oldPaths = new ArrayList<>(); LoadedApk.makePaths(this, ai, oldPaths); packageInfo.updateApplicationInfo(ai, oldPaths); } if (packageInfo.isSecurityViolation() && (flags&Context.CONTEXT_IGNORE_SECURITY) == 0) { throw new SecurityException( "Requesting code from " + packageName + " to be run in process " + mBoundApplication.processName + "/" + mBoundApplication.appInfo.uid); } return packageInfo; } } if (ai != null) { return getPackageInfo(ai, compatInfo, flags); } return null; } @UnsupportedAppUsage(trackingBug = 171933273) public final LoadedApk getPackageInfo(ApplicationInfo ai, CompatibilityInfo compatInfo, int flags) { boolean includeCode = (flags&Context.CONTEXT_INCLUDE_CODE) != 0; boolean securityViolation = includeCode && ai.uid != 0 && ai.uid != Process.SYSTEM_UID && (mBoundApplication != null ? !UserHandle.isSameApp(ai.uid, mBoundApplication.appInfo.uid) : true); boolean registerPackage = includeCode && (flags&Context.CONTEXT_REGISTER_PACKAGE) != 0; if ((flags&(Context.CONTEXT_INCLUDE_CODE |Context.CONTEXT_IGNORE_SECURITY)) == Context.CONTEXT_INCLUDE_CODE) { if (securityViolation) { String msg = "Requesting code from " + ai.packageName + " (with uid " + ai.uid + ")"; if (mBoundApplication != null) { msg = msg + " to be run in process " + mBoundApplication.processName + " (with uid " + mBoundApplication.appInfo.uid + ")"; } throw new SecurityException(msg); } } return getPackageInfo(ai, compatInfo, null, securityViolation, includeCode, registerPackage); }4. App 创建 Application对象
(20230322更新)
单进程，创建1个application对象，实验一次onCreate()方法
多进程(N)，创建N个application对象，实验N次onCreate()方法
固然Application的假造内存地址类似（打印出来的），但它们的真实物理地址却差别
反射去调用Java的 "sun.misc.Unsafe" 类，获取物理内存地址.
参考>https://juejin.cn/post/7208345469658415159
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