答: PackageManagerService（简称 【PKMS】），是 Android 系统中核心服务之一，负责应用程序的安装，卸载，信息查询，解析等工作。与apk相关的信息都在这个服务里可以查询到。
a、简单来需知：PKMS 与 AMS 一样，也是Android系统核心服务之一，非常非常的重要，主要完成以下核心功能：
说白了，就是解析apk，扫描apk，管理apk，三部曲进行的；
b、分析的核心源码路径地址如下：
/frameworks/base/core/java/android/app/ApplicationPackageManager.java
/frameworks/base/services/java/com/android/server/SystemServer.java
/frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java
/frameworks/base/services/core/java/com/android/server/pm/PackageDexOptimizer.java
/frameworks/base/services/core/java/com/android/server/pm/Installer.java
/frameworks/base/services/core/java/com/android/server/pm/Settings.java
/frameworks/base/services/core/java/com/android/server/pm/permission/BasePermission.java
/frameworks/base/services/core/java/com/android/server/pm/PackageManagerService.java
/frameworks/base/services/core/java/com/android/server/pm/permission/DefaultPermissionGrantPolicy.java
/frameworks/base/services/core/java/com/android/server/pm/permission/PermissionManagerService.java
/frameworks/base/core/java/android/content/pm/IPackageManager.aidl
/frameworks/base/core/java/android/content/pm/PackageManager.java
/frameworks/base/core/java/com/android/server/SystemConfig.java
a、代码的结构如下：
public class PackageManagerService extends IPackageManager.Stub
implements PackageSender {
......
}
public abstract class PackageManager {
......
}
public class ApplicationPackageManager extends PackageManager {
......
}
public interface IPackageManager extends android.os.IInterface {
/** Local-side IPC implementation stub class. */
public static abstract class Stub extends android.os.Binder
implements android.content.pm.IPackageManager {
private static final java.lang.String DESCRIPTOR = "android.content.pm.IPackageManager";
/** Construct the stub at attach it to the interface. */
public Stub() {
this.attachInterface(this, DESCRIPTOR);
}
......
}
private static class Proxy implements android.content.pm.IPackageManager {
private android.os.IBinder mRemote;
Proxy(android.os.IBinder remote) {
mRemote = remote;
}
@Override public android.os.IBinder asBinder() {
return mRemote;
}
......
}
......
}
b、客户端可通过【Context.getPackageManager()】获得【ApplicationPackageManager】对象, 而【mPM】指向的是【Proxy代理】，当调用到mPM.方法后，将会调用到IPackageManager的Proxy代理方法，然后通过Binder机制中的【mRemote】与服务端【PackageManagerService】通信 并调用到PackageManagerService的方法；
public class ContextWrapper extends Context {
Context mBase;
public PackageManager getPackageManager() {
return mBase.getPackageManager();
}
}
public class ContextImpl extends Context {
public PackageManager getPackageManager() {
if (mPackageManager != null) {
return mPackageManager;
}
//通过ActivityThread类获取的；
IPackageManager pm = ActivityThread.getPackageManager();
if (pm != null) {
// Doesn't matter if we make more than one instance.
return (mPackageManager = new ApplicationPackageManager(this, pm));
}
return null;
}
}
// 应用程序的入口类
public final class ActivityThread {
//静态可见的接口类
static volatile IPackageManager sPackageManager;
public static IPackageManager getPackageManager() {
if (sPackageManager != null) {
//Slog.v("PackageManager", "returning cur default = " + sPackageManager);
return sPackageManager;
}
IBinder b = ServiceManager.getService("package");
//Slog.v("PackageManager", "default service binder = " + b);
sPackageManager = IPackageManager.Stub.asInterface(b);
//Slog.v("PackageManager", "default service = " + sPackageManager);
return sPackageManager;
}
}
public class ApplicationPackageManager extends PackageManager {
private final IPackageManager mPM;//真正的接口
protected ApplicationPackageManager(ContextImpl context,
IPackageManager pm) {
mContext = context;
mPM = pm;
}
}c、自我总结：PKMS是属于Binder机制的服务端角色，客户端通过Context对象获取接口类对象
a、PKMS的过程图如下：
b、PKMS启动过程描述：
b.1、SystemServer启动PKMS： 先是在【SystemServer.startBootstrapServices()】函数中启动PKMS服务，
b.2、再调用【startOtherServices()】函数中对dex优化，磁盘管理功能，让PKMS进入【systemReady】状态。
c、SystemServer调用PKMS的七步流程：
c.0、SystemServer.java中的run函数，通过调用SystemServer.startBootstrapServices()函数中启动PKMS服务，在调用startOtherServices()函数；
c.1、第一步：startBootstrapServices()首先启动Installer服务，也就是【安装器】，随后判断当前的设备是否处于加密状态，如果是则只是【解析核心应用】，接着调用PackageManagerService的静态方法main来【创建pkms对象】
// 第一步：启动Installer
// 阻塞等待installd完成启动，以便有机会创建具有适当权限的关键目录，如/data/user。
// 我们需要在初始化其他服务之前完成此任务。
traceBeginAndSlog("StartInstaller");
Installer installer = mSystemServiceManager.startService(Installer.class);
traceEnd();c.2、第二部：通过系统属性【"vold.decrypt"】，获取是否有加密设备，同时判断是否仅仅处理核心服务
// 第二步：获取设别是否加密(手机设置密码)，如果设备加密了，则只解析"core"应用，mOnlyCore
= true，后面会频繁使用该变量进行条件判断
String cryptState = SystemProperties.get("vold.decrypt");
if (ENCRYPTING_STATE.equals(cryptState)) {
Slog.w(TAG, "Detected encryption in progress - only parsing core apps");
mOnlyCore = true;
} else if (ENCRYPTED_STATE.equals(cryptState)) {
Slog.w(TAG, "Device encrypted - only parsing core apps");
mOnlyCore = true;
}c.3、第三部：调用PKMS.main方法，实例化PKMS
/
/ 第三步：调用main方法初始化PackageManagerService
traceBeginAndSlog("StartPackageManagerService");
mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
// PKMS是否是第一次启动
mFirstBoot = mPackageManagerService.isFirstBoot();
// 定义一个引用；
mPackageManager = mSystemContext.getPackageManager();
traceEnd();PKMS.main方法：
public static PackageManagerService main(Context context, Installer installer,
boolean factoryTest, boolean onlyCore) {
// Self-check for initial settings.自检查初始化设置的属性
PackageManagerServiceCompilerMapping.checkProperties();
// 新建PKMS的对象，
PackageManagerService m = new PackageManagerService(context, installer,
factoryTest, onlyCore);
m.enableSystemUserPackages();
ServiceManager.addService("package", m);//将服务添加到SM中
final PackageManagerNative pmn = m.new PackageManagerNative();
ServiceManager.addService("package_native", pmn);//将服务添加到SM中
return m;
}c.4、第四步：如果设备没有加密，操作它，管理A/B OTA dexopting,主要依据mOnlyCore来做判断，为false表没有加密
// Manages A/B OTA dexopting. This is a bootstrap service as we need it to rename
// A/B artifacts after boot, before anything else might touch/need them.
// Note: this isn't needed during decryption (we don't have /data anyways).
// 第四步：如果设备没有加密，操作它。管理A/B OTA dexopting。
if (!mOnlyCore) {
boolean disableOtaDexopt = SystemProperties.getBoolean("config.disable_otadexopt",
false);
if (!disableOtaDexopt) {
traceBeginAndSlog("StartOtaDexOptService");
try {//激活OTA服务
OtaDexoptService.main(mSystemContext, mPackageManagerService);
} catch (Throwable e) {
reportWtf("starting OtaDexOptService", e);
} finally {
traceEnd();
}
}
}c.5、第五步：如果设备没有加密，执行【updatePackagesIfNeeded】函数，调用PKMS的【performDexOptUpgrade】完成dex优化；
if (!mOnlyCore) {
traceBeginAndSlog("UpdatePackagesIfNeeded");
try {//啥事情都没有干，只是转掉
// 第五步：如果设备没有加密，执行performDexOptUpgrade，完成dex优化；
mPackageManagerService.updatePackagesIfNeeded();
} catch (Throwable e) {
reportWtf("update packages", e);
}
traceEnd();
}c.6、第六步：执行【performFstrimIfNeeded】函数，这里有一个显示UI,是否需要显示："正在优化存储空间。"
traceBeginAndSlog("PerformFstrimIfNeeded");
try {
// 第六步：最终执行performFstrim，完成磁盘维护
mPackageManagerService.performFstrimIfNeeded();
} catch (Throwable e) {
reportWtf("performing fstrim", e);
}
traceEnd();c.7、第七步：执行【systemReady()】，说明PKMS已经准备就绪，这里就是做最后的工作
traceBeginAndSlog("MakePackageManagerServiceReady");
try {
// 第七步：PKMS准备就绪
mPackageManagerService.systemReady();
} catch (Throwable e) {
reportWtf("making Package Manager Service ready", e);
}
traceEnd();c.8、分析PKSM，重点需要从第三部开始，下一篇继续分析；
PackageManagerService Android 8.1 源码解读 02