引言

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SystemServer行程在執行startBootstrapServices方法后，首先就通過SystemServiceManager創建和啟動Installer系統服務，

以后更多精選系列文章以高度完整的系列形式發布在公眾號，真正的形成一套完整的技術堆疊，歡迎關注，目前第一個系列是關于Android系統啟動系列的文章，大概有二十幾篇干貨，

• Android 進階——系統啟動之BootLoader 簡介及內核啟動（一）
• Android 進階——系統啟動之Linux init行程的創建和啟動（二）
• Android 進階——系統啟動之Android init行程的創建和啟動（三）
• Android 進階——系統啟動之Android init.rc腳本決議（四）
• Android 進階——系統啟動之Android init行程決議init.rc腳本（五）
• Android 進階——系統啟動之Android行程造物者Zygote 行程啟動詳解（六）
• Android 進階——系統啟動之核心SystemServer行程啟動詳解（七）
• Android 進階——系統啟動之SystemServer創建并啟動Installer服務（八）

一、Intsaller系統服務概述

\frameworks\base\services\core\java\com\android\server\pm\Installer.java繼承自com.android.server.SystemService，同時持有installd守護行程對應Binder服務的代理物件，本質上就是通過Binder呼叫去與Linux底層installd守護行程通信完成真正的完成Apk檔案格式的優化和轉換、建立相關的資料目錄、洗掉檔案、安裝應用等作業，因此在其他系統核心服務啟動前首先被啟動，

    private void startBootstrapServices() {
    	...
       Installer installer = mSystemServiceManager.startService(Installer.class);

當SystemServiceManager.startService(Installer.class)觸發com.android.server.pm.Installer#onStart回呼時，首先通過ServerManager獲取名為installdBinder服務代理物件，然后呼叫這個Binder服務代理物件通過socket與Linux的installd 守護行程通信，

package com.android.server.pm;

import com.android.internal.os.BackgroundThread;
import com.android.server.SystemService;
public class Installer extends SystemService {
    private volatile IInstalld mInstalld;

    public Installer(Context context, boolean isolated) {
        super(context);
        mIsolated = isolated;
    }

    @Override
    public void onStart() {
        if (mIsolated) {
            mInstalld = null;
        } else {
            connect();
        }
    }

    private void connect() {
        IBinder binder = ServiceManager.getService("installd");
        if (binder != null) {
            try {
                binder.linkToDeath(new DeathRecipient() {
                    @Override
                    public void binderDied() {
                        Slog.w(TAG, "installd died; reconnecting");
                        connect();
                    }
                }, 0);
            }
        }

        if (binder != null) {
            mInstalld = IInstalld.Stub.asInterface(binder);
            try {
                invalidateMounts();
            }
        } else {
            Slog.w(TAG, "installd not found; trying again");
            BackgroundThread.getHandler().postDelayed(() -> {
                connect();
            }, DateUtils.SECOND_IN_MILLIS);
        }
    }
    public void dexopt(String apkPath, int uid, @Nullable String pkgName, String instructionSet,
            int dexoptNeeded, @Nullable String outputPath, int dexFlags,
            String compilerFilter, @Nullable String volumeUuid, @Nullable String sharedLibraries,
            @Nullable String seInfo, boolean downgrade, int targetSdkVersion,
            @Nullable String profileName, @Nullable String dexMetadataPath,
            @Nullable String compilationReason) throws InstallerException {
        if (!checkBeforeRemote()) return;
        try {
            mInstalld.dexopt(apkPath, uid, pkgName, instructionSet, dexoptNeeded, outputPath,
                    dexFlags, compilerFilter, volumeUuid, sharedLibraries, seInfo, downgrade,
                    targetSdkVersion, profileName, dexMetadataPath, compilationReason);
        }
    }
    public void rmdex(String codePath, String instructionSet) throws InstallerException {
        try {
            mInstalld.rmdex(codePath, instructionSet);
        }
    }
    public void createUserData(String uuid, int userId, int userSerial, int flags)
            throws InstallerException {
        if (!checkBeforeRemote()) return;
        try {
            mInstalld.createUserData(uuid, userId, userSerial, flags);
        }
    }
	...
    public void linkNativeLibraryDirectory(String uuid, String packageName, String nativeLibPath32,
            int userId) throws InstallerException {
        if (!checkBeforeRemote()) return;
        try {
            mInstalld.linkNativeLibraryDirectory(uuid, packageName, nativeLibPath32, userId);
        }
    }
    public void createOatDir(String oatDir, String dexInstructionSet)
            throws InstallerException {
        if (!checkBeforeRemote()) return;
        try {
            mInstalld.createOatDir(oatDir, dexInstructionSet);
        }
    }
    public void linkFile(String relativePath, String fromBase, String toBase)
            throws InstallerException {
        if (!checkBeforeRemote()) return;
        try {
            mInstalld.linkFile(relativePath, fromBase, toBase);
        }
    }
    public void deleteOdex(String apkPath, String instructionSet, String outputPath)
            throws InstallerException {
            mInstalld.deleteOdex(apkPath, instructionSet, outputPath);
    }
    public void installApkVerity(String filePath, FileDescriptor verityInput, int contentSize)
            throws InstallerException {
        if (!checkBeforeRemote()) return;
         mInstalld.installApkVerity(filePath, verityInput, contentSize);
    }
    public boolean reconcileSecondaryDexFile(String apkPath, String packageName, int uid,
            String[] isas, @Nullable String volumeUuid, int flags) throws InstallerException {
            return mInstalld.reconcileSecondaryDexFile(apkPath, packageName, uid, isas,
                    volumeUuid, flags);
    }

    public void invalidateMounts() throws InstallerException {
        if (!checkBeforeRemote()) return;
            mInstalld.invalidateMounts();
    }
    ...
}

二、com.android.server.SystemService概述

\frameworks\base\services\core\java\com\android\server\SystemService.java本質上就是對于一些運行在系統行程服務進行了抽象，定義了一些統一的生命周期方法和運行規則（所有方法都必須在系統服務行程的main looper thread中被呼叫），

package com.android.server;

import android.os.ServiceManager;
/**
 * The base class for services running in the system process. Override and implement
 * the lifecycle event callback methods as needed.
 * {@hide}
 */
public abstract class SystemService {
    ...
    private final Context mContext;
    public SystemService(Context context) {
        mContext = context;
    }
    public abstract void onStart();
		...
    protected final void publishBinderService(String name, IBinder service) {
        publishBinderService(name, service, false);
    }
    protected final void publishBinderService(String name, IBinder service,
            boolean allowIsolated) {
        ServiceManager.addService(name, service, allowIsolated);
    }
    protected final IBinder getBinderService(String name) {
        return ServiceManager.getService(name);
    }
    protected final <T> void publishLocalService(Class<T> type, T service) {
        LocalServices.addService(type, service);
    }
    protected final <T> T getLocalService(Class<T> type) {
        return LocalServices.getService(type);
    }

    private SystemServiceManager getManager() {
        return LocalServices.getService(SystemServiceManager.class);
    }
}

三、Intsaller系統服務的啟動

1、com.android.server.SystemServer#startBootstrapServices 觸發Installer系統服務啟動

    private void startBootstrapServices() {
        Installer installer = mSystemServiceManager.startService(Installer.class);

2、com.android.server.SystemServiceManager#startService反射創建并回呼com.android.server.pm.Installer#onStart

\frameworks\base\services\core\java\com\android\server\SystemServiceManager.java

2.1、com.android.server.SystemServiceManager#startService(String className)獲取Installer的位元組碼物件

    public SystemService startService(String className) {
        final Class<SystemService> serviceClass;
        serviceClass = (Class<SystemService>)Class.forName(className);
        return startService(serviceClass);
    }

2.2、com.android.server.SystemServiceManager#startService(java.lang.Class< T >)反射創建Installer物件

 /**
     * Creates and starts a system service. The class must be a subclass of
     * {@link com.android.server.SystemService}.
     */
    public <T extends SystemService> T startService(Class<T> serviceClass) {
        try {
            final String name = serviceClass.getName();
            // Create the service.
            final T service;
            try {
                Constructor<T> constructor = serviceClass.getConstructor(Context.class);
                service = constructor.newInstance(mContext);
            } 
            startService(service);
            return service;
        }
    }

2.3、com.android.server.SystemServiceManager#startService(SystemService) 注冊到SystemServerManager并觸發Installer#onStart回呼

 public void startService(@NonNull final SystemService service) {
        // @link ArrayList<SystemService> mServices 注冊到SystemServerManager中
        mServices.add(service);
        long time = SystemClock.elapsedRealtime();
        try {
            service.onStart();
        }
        warnIfTooLong(SystemClock.elapsedRealtime() - time, service, "onStart");
    }

3、com.android.server.pm.Installer#onStart 獲取installd 的Binder服務代理物件

3.1、com.android.server.pm.Installer#onStart 觸發獲取installd 的Binder服務代理物件

    @Override
    public void onStart() {
        if (mIsolated) {
            mInstalld = null;
        } else {
            connect();
        }
    } 

3.2、com.android.server.pm.Installer#connect 真正獲取installd 的Binder服務代理物件

    private void connect() {
    	//首先通過ServiceManager 獲取installd服務的Binder物件
        IBinder binder = ServiceManager.getService("installd");
        if (binder != null) {
            try {
                binder.linkToDeath(new DeathRecipient() {
                    @Override
                    public void binderDied() {
                        Slog.w(TAG, "installd died; reconnecting");
                        connect();
                    }
                }, 0);
            } catch (RemoteException e) {
                binder = null;
            }
        }

        if (binder != null) {
            //把Binder物件轉為具體的Binder服務物件
            mInstalld = IInstalld.Stub.asInterface(binder);
            try {
                invalidateMounts();
            } catch (InstallerException ignored) {
            }
        } else {
            Slog.w(TAG, "installd not found; trying again");
            BackgroundThread.getHandler().postDelayed(() -> {
                connect();
            }, DateUtils.SECOND_IN_MILLIS);
        }
    }

至此Installer系統服務啟動完畢，接著真正開始其他系統服務的啟動，敬請參見下集，