深入理解Android Instant Run运行机制

Instant Run

Instant Run，是android studio2.0新增的一个运行机制，在你编码开发、测试或debug的时候，它都能显著减少你对当前应用的构建和部署的时间。通俗的解释就是，当你在Android Studio中改了你的代码，Instant Run可以很快的让你看到你修改的效果。而在没有Instant Run之前，你的一个小小的修改，都肯能需要几十秒甚至更长的等待才能看到修改后的效果。

传统的代码修改及编译部署流程

传统的代码修改及编译流程如下：构建整个apk → 部署app → app重启 → 重启Activity

Instant Run编译和部署流程

Instant Run构建项目的流程：构建修改的部分 → 部署修改的dex或资源 → 热部署，温部署，冷部署

热拔插，温拔插，冷拔插

热拔插：代码改变被应用、投射到APP上，不需要重启应用，不需要重建当前activity。
场景：适用于多数的简单改变（包括一些方法实现的修改，或者变量值修改）
**温拔插：**activity需要被重启才能看到所需更改。
场景：典型的情况是代码修改涉及到了资源文件，即resources。
**冷拔插：**app需要被重启（但是仍然不需要重新安装）
场景：任何涉及结构性变化的，比如：修改了继承规则、修改了方法签名等。

首次运行Instant Run，Gradle执行过程

一个新的App Server类会被注入到App中，与Bytecode instrumentation协同监控代码的变化。
同时会有一个新的Application类，它注入了一个自定义类加载器（Class Loader）,同时该Application类会启动我们所需的新注入的App Server。于是，Manifest会被修改来确保我们的应用能使用这个新的Application类。（这里不必担心自己继承定义了Application类，Instant Run添加的这个新Application类会代理我们自定义的Application类）
至此，Instant Run已经可以跑起来了，在我们使用的时候，它会通过决策，合理运用冷温热拔插来协助我们大量地缩短构建程序的时间。

在Instant Run运行之前，Android Studio会检查是否能连接到App Server中。并且确保这个App Server是Android Studio所需要的。这同样能确保该应用正处在前台。

热拔插

Android Studio monitors： 运行着Gradle任务来生成增量.dex文件（这个dex文件是对应着开发中的修改类） Android Studio会提取这些.dex文件发送到App Server，然后部署到App（Gradle修改class的原理，请戳链接）。

App Server会不断监听是否需要重写类文件，如果需要，任务会被立马执行。新的更改便能立即被响应。我们可以通过打断点的方式来查看。

温拔插

温拔插需要重启Activity，因为资源文件是在Activity创建时加载，所以必须重启Activity来重载资源文件。
目前来说，任何资源文件的修改都会导致重新打包再发送到APP。但是，google的开发团队正在致力于开发一个增量包，这个增量包只会包装修改过的资源文件并能部署到当前APP上。
所以温拔插实际上只能应对少数的情况，它并不能应付应用在架构、结构上的变化。

注：温拔插涉及到的资源文件修改，在manifest上是无效的（这里的无效是指不会启动Instant Run），因为，manifest的值是在APK安装的时候被读取，所以想要manifest下资源的修改生效，还需要触发一个完整的应用构建和部署。

冷拔插

应用部署的时候，会把工程拆分成十个部分，每部分都拥有自己的.dex文件，然后所有的类会根据包名被分配给相应的.dex文件。当冷拔插开启时，修改过的类所对应的.dex文件，会重组生成新的.dex文件，然后再部署到设备上。
之所以能这么做，是依赖于Android的ART模式，它能允许加载多个.dex文件。ART模式在android4.4（API-19）中加入，但是Dalvik依然是首选，到了android5.0（API-21），ART模式才成为系统默认首选，所以Instant Run只能运行在API-21及其以上版本。

使用Instant Run一些注意点

Instant Run是被Android Studio控制的。所以我们只能通过IDE来启动它，如果通过设备来启动应用，Instant Run会出现异常情况。在使用Instant Run来启动Android app的时候，应注意以下几点：

1. 如果应用的minSdkVersion小于21，可能多数的Instant Run功能会挂掉，这里提供一个解决方法，通过product flavor建立一个minSdkVersion大于21的新分支，用来debug。
2. Instant Run目前只能在主进程里运行，如果应用是多进程的，类似微信，把webView抽出来单独一个进程，那热、温拔插会被降级为冷拔插。
3. 在Windows下，Windows Defender Real-Time Protection可能会导致Instant Run挂掉，可用通过添加白名单列表解决。
4. 暂时不支持Jack compiler，Instrumentation Tests，或者同时部署到多台设备。

结合Demo深度理解

为了方便大家的理解，我们新建一个项目，里面不写任何的逻辑功能，只对application做一个修改：

首先，我们先反编译一下APK的构成，使用的工具：d2j-dex2jar 和jd-gui。

我们要看的启动的信息就在这个instant-run.zip文件里面，解压instant-run.zip，我们会发现，我们真正的业务代码都在这里。

从instant-run文件中我们猜想是BootstrapApplication替换了我们的application，Instant-Run代码作为一个宿主程序，将app作为资源dex加载起来。

那么InstantRun是怎么把业务代码运行起来的呢？

Instant Run如何启动app

按照我们上面对instant-run运行机制的猜想，我们首先看一下appliaction的分析attachBaseContext和onCreate方法。

attachBaseContext()

protected void attachBaseContext(Context context) {if (!AppInfo.usingApkSplits) {String apkFile = context.getApplicationInfo().sourceDir;long apkModified = apkFile != null ? new File(apkFile).lastModified() : 0L;createResources(apkModified);setupClassLoaders(context, context.getCacheDir().getPath(),apkModified);}createRealApplication();super.attachBaseContext(context);if (this.realApplication != null) {try {Method attachBaseContext = ContextWrapper.class.getDeclaredMethod("attachBaseContext",new Class[] { Context.class });attachBaseContext.setAccessible(true);attachBaseContext.invoke(this.realApplication,new Object[] { context });} catch (Exception e) {throw new IllegalStateException(e);}}}

我们依次需要关注的方法有：
createResources → setupClassLoaders → createRealApplication → 调用realApplication的attachBaseContext方法

createResources()

private void createResources(long apkModified) {FileManager.checkInbox();File file = FileManager.getExternalResourceFile();this.externalResourcePath = (file != null ? file.getPath() : null);if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Resource override is "+ this.externalResourcePath);}if (file != null) {try {long resourceModified = file.lastModified();if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Resource patch last modified: "+ resourceModified);Log.v("InstantRun", "APK last modified: " + apkModified+ " "+ (apkModified > resourceModified ? ">" : "<")+ " resource patch");}if ((apkModified == 0L) || (resourceModified <= apkModified)) {if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun","Ignoring resource file, older than APK");}this.externalResourcePath = null;}} catch (Throwable t) {Log.e("InstantRun", "Failed to check patch timestamps", t);}}}

说明：该方法主要是判断资源resource.ap_是否改变，然后保存resource.ap_的路径到externalResourcePath中。

setupClassLoaders()

private static void setupClassLoaders(Context context, String codeCacheDir,long apkModified) {List dexList = FileManager.getDexList(context, apkModified);Class server = Server.class;Class patcher = MonkeyPatcher.class;if (!dexList.isEmpty()) {if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Bootstrapping class loader with dex list "+ join('\n', dexList));}ClassLoader classLoader = BootstrapApplication.class.getClassLoader();String nativeLibraryPath;try {nativeLibraryPath = (String) classLoader.getClass().getMethod("getLdLibraryPath", new Class[0]).invoke(classLoader, new Object[0]);if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Native library path: "+ nativeLibraryPath);}} catch (Throwable t) {Log.e("InstantRun", "Failed to determine native library path "+ t.getMessage());nativeLibraryPath = FileManager.getNativeLibraryFolder().getPath();}IncrementalClassLoader.inject(classLoader, nativeLibraryPath,codeCacheDir, dexList);}}

说明，该方法是初始化一个ClassLoaders并调用IncrementalClassLoader。
IncrementalClassLoader的源码如下：

public class IncrementalClassLoader extends ClassLoader {public static final boolean DEBUG_CLASS_LOADING = false;private final DelegateClassLoader delegateClassLoader;public IncrementalClassLoader(ClassLoader original,String nativeLibraryPath, String codeCacheDir, List dexes) {super(original.getParent());this.delegateClassLoader = createDelegateClassLoader(nativeLibraryPath,codeCacheDir, dexes, original);}public Class findClass(String className) throws ClassNotFoundException {try {return this.delegateClassLoader.findClass(className);} catch (ClassNotFoundException e) {throw e;}}private static class DelegateClassLoader extends BaseDexClassLoader {private DelegateClassLoader(String dexPath, File optimizedDirectory,String libraryPath, ClassLoader parent) {super(dexPath, optimizedDirectory, libraryPath, parent);}public Class findClass(String name) throws ClassNotFoundException {try {return super.findClass(name);} catch (ClassNotFoundException e) {throw e;}}}private static DelegateClassLoader createDelegateClassLoader(String nativeLibraryPath, String codeCacheDir, List dexes,ClassLoader original) {String pathBuilder = createDexPath(dexes);return new DelegateClassLoader(pathBuilder, new File(codeCacheDir),nativeLibraryPath, original);}private static String createDexPath(List dexes) {StringBuilder pathBuilder = new StringBuilder();boolean first = true;for (String dex : dexes) {if (first) {first = false;} else {pathBuilder.append(File.pathSeparator);}pathBuilder.append(dex);}if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Incremental dex path is "+ BootstrapApplication.join('\n', dexes));}return pathBuilder.toString();}private static void setParent(ClassLoader classLoader, ClassLoader newParent) {try {Field parent = ClassLoader.class.getDeclaredField("parent");parent.setAccessible(true);parent.set(classLoader, newParent);} catch (IllegalArgumentException e) {throw new RuntimeException(e);} catch (IllegalAccessException e) {throw new RuntimeException(e);} catch (NoSuchFieldException e) {throw new RuntimeException(e);}}public static ClassLoader inject(ClassLoader classLoader,String nativeLibraryPath, String codeCacheDir, List dexes) {IncrementalClassLoader incrementalClassLoader = new IncrementalClassLoader(classLoader, nativeLibraryPath, codeCacheDir, dexes);setParent(classLoader, incrementalClassLoader);return incrementalClassLoader;}}

inject方法是用来设置classloader的父子顺序的，使用IncrementalClassLoader来加载dex。由于ClassLoader的双亲委托模式，也就是委托父类加载类，父类中找不到再在本ClassLoader中查找。
调用的效果图如下：

为了方便我们对委托父类加载机制的理解，我们可以做一个实验，在我们的application做一些Log。

@Overridepublic void onCreate() {super.onCreate();try{Log.d(TAG,"###onCreate in myApplication");String classLoaderName = getClassLoader().getClass().getName();Log.d(TAG,"###onCreate in myApplication classLoaderName = "+classLoaderName);String parentClassLoaderName = getClassLoader().getParent().getClass().getName();Log.d(TAG,"###onCreate in myApplication parentClassLoaderName = "+parentClassLoaderName);String pParentClassLoaderName = getClassLoader().getParent().getParent().getClass().getName();Log.d(TAG,"###onCreate in myApplication pParentClassLoaderName = "+pParentClassLoaderName);}catch (Exception e){e.printStackTrace();}}

输出结果：

03-20 10:43:42.475 27307-27307/mobctrl.net.testinstantrun D/MyApplication: ###onCreate in myApplication classLoaderName = dalvik.system.PathClassLoader03-20 10:43:42.475 27307-27307/mobctrl.net.testinstantrun D/MyApplication: ###onCreate in myApplication parentClassLoaderName = com.android.tools.fd.runtime.IncrementalClassLoader03-20 10:43:42.475 27307-27307/mobctrl.net.testinstantrun D/MyApplication: ###onCreate in myApplication pParentClassLoaderName = java.lang.BootClassLoader

由此，我们知道，当前PathClassLoader委托IncrementalClassLoader加载dex。

我们继续对attachBaseContext()继续分析：

attachBaseContext.invoke(this.realApplication,new Object[] { context });

createRealApplication

private void createRealApplication() {if (AppInfo.applicationClass != null) {if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun","About to create real application of class name = "+ AppInfo.applicationClass);}try {Class realClass = (Class) Class.forName(AppInfo.applicationClass);if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun","Created delegate app class successfully : "+ realClass + " with class loader "+ realClass.getClassLoader());}Constructor constructor = realClass.getConstructor(new Class[0]);this.realApplication = ((Application) constructor.newInstance(new Object[0]));if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun","Created real app instance successfully :"+ this.realApplication);}} catch (Exception e) {throw new IllegalStateException(e);}} else {this.realApplication = new Application();}}

该方法就是用classes.dex中的AppInfo类的applicationClass常量中保存的app真实的application。由例子的分析我们可以知道applicationClass就是com.xzh.demo.MyApplication。通过反射的方式，创建真是的realApplication。
看完attachBaseContext我们继续看BootstrapApplication();

BootstrapApplication()

我们首先看一下onCreate方法：

onCreate()

public void onCreate() {if (!AppInfo.usingApkSplits) {MonkeyPatcher.monkeyPatchApplication(this, this,this.realApplication, this.externalResourcePath);MonkeyPatcher.monkeyPatchExistingResources(this,this.externalResourcePath, null);} else {MonkeyPatcher.monkeyPatchApplication(this, this,this.realApplication, null);}super.onCreate();if (AppInfo.applicationId != null) {try {boolean foundPackage = false;int pid = Process.myPid();ActivityManager manager = (ActivityManager) getSystemService("activity");List processes = manager.getRunningAppProcesses();boolean startServer = false;if ((processes != null) && (processes.size() > 1)) {for (ActivityManager.RunningAppProcessInfo processInfo : processes) {if (AppInfo.applicationId.equals(processInfo.processName)) {foundPackage = true;if (processInfo.pid == pid) {startServer = true;break;}}}if ((!startServer) && (!foundPackage)) {startServer = true;if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun","Multiprocess but didn't find process with package: starting server anyway");}}} else {startServer = true;}if (startServer) {Server.create(AppInfo.applicationId, this);}} catch (Throwable t) {if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Failed during multi process check", t);}Server.create(AppInfo.applicationId, this);}}if (this.realApplication != null) {this.realApplication.onCreate();}}

在onCreate()中我们需要注意以下方法：
monkeyPatchApplication → monkeyPatchExistingResources → Server启动 → 调用realApplication的onCreate方法

monkeyPatchApplication

public static void monkeyPatchApplication(Context context,Application bootstrap, Application realApplication,String externalResourceFile) {try {Class activityThread = Class.forName("android.app.ActivityThread");Object currentActivityThread = getActivityThread(context,activityThread);Field mInitialApplication = activityThread.getDeclaredField("mInitialApplication");mInitialApplication.setAccessible(true);Application initialApplication = (Application) mInitialApplication.get(currentActivityThread);if ((realApplication != null) && (initialApplication == bootstrap)) {mInitialApplication.set(currentActivityThread, realApplication);}if (realApplication != null) {Field mAllApplications = activityThread.getDeclaredField("mAllApplications");mAllApplications.setAccessible(true);List allApplications = (List) mAllApplications.get(currentActivityThread);for (int i = 0; i < allApplications.size(); i++) {if (allApplications.get(i) == bootstrap) {allApplications.set(i, realApplication);}}}Class loadedApkClass;try {loadedApkClass = Class.forName("android.app.LoadedApk");} catch (ClassNotFoundException e) {loadedApkClass = Class.forName("android.app.ActivityThread$PackageInfo");}Field mApplication = loadedApkClass.getDeclaredField("mApplication");mApplication.setAccessible(true);Field mResDir = loadedApkClass.getDeclaredField("mResDir");mResDir.setAccessible(true);Field mLoadedApk = null;try {mLoadedApk = Application.class.getDeclaredField("mLoadedApk");} catch (NoSuchFieldException e) {}for (String fieldName : new String[] { "mPackages","mResourcePackages" }) {Field field = activityThread.getDeclaredField(fieldName);field.setAccessible(true);Object value = field.get(currentActivityThread);for (Map.Entry> entry : ((Map>) value).entrySet()) {Object loadedApk = ((WeakReference) entry.getValue()).get();if (loadedApk != null) {if (mApplication.get(loadedApk) == bootstrap) {if (realApplication != null) {mApplication.set(loadedApk, realApplication);}if (externalResourceFile != null) {mResDir.set(loadedApk, externalResourceFile);}if ((realApplication != null)&& (mLoadedApk != null)) {mLoadedApk.set(realApplication, loadedApk);}}}}}} catch (Throwable e) {throw new IllegalStateException(e);}}

说明：该方法的作用是替换所有当前app的application为realApplication。
替换的过程如下：
1.替换ActivityThread的mInitialApplication为realApplication
2.替换mAllApplications 中所有的Application为realApplication
3.替换ActivityThread的mPackages,mResourcePackages中的mLoaderApk中的application为realApplication。

monkeyPatchExistingResources

public static void monkeyPatchExistingResources(Context context,String externalResourceFile, Collection activities) {if (externalResourceFile == null) {return;}try {AssetManager newAssetManager = (AssetManager) AssetManager.class.getConstructor(new Class[0]).newInstance(new Object[0]);Method mAddAssetPath = AssetManager.class.getDeclaredMethod("addAssetPath", new Class[] { String.class });mAddAssetPath.setAccessible(true);if (((Integer) mAddAssetPath.invoke(newAssetManager,new Object[] { externalResourceFile })).intValue() == 0) {throw new IllegalStateException("Could not create new AssetManager");}Method mEnsureStringBlocks = AssetManager.class.getDeclaredMethod("ensureStringBlocks", new Class[0]);mEnsureStringBlocks.setAccessible(true);mEnsureStringBlocks.invoke(newAssetManager, new Object[0]);if (activities != null) {for (Activity activity : activities) {Resources resources = activity.getResources();try {Field mAssets = Resources.class.getDeclaredField("mAssets");mAssets.setAccessible(true);mAssets.set(resources, newAssetManager);} catch (Throwable ignore) {Field mResourcesImpl = Resources.class.getDeclaredField("mResourcesImpl");mResourcesImpl.setAccessible(true);Object resourceImpl = mResourcesImpl.get(resources);Field implAssets = resourceImpl.getClass().getDeclaredField("mAssets");implAssets.setAccessible(true);implAssets.set(resourceImpl, newAssetManager);}Resources.Theme theme = activity.getTheme();try {try {Field ma = Resources.Theme.class.getDeclaredField("mAssets");ma.setAccessible(true);ma.set(theme, newAssetManager);} catch (NoSuchFieldException ignore) {Field themeField = Resources.Theme.class.getDeclaredField("mThemeImpl");themeField.setAccessible(true);Object impl = themeField.get(theme);Field ma = impl.getClass().getDeclaredField("mAssets");ma.setAccessible(true);ma.set(impl, newAssetManager);}Field mt = ContextThemeWrapper.class.getDeclaredField("mTheme");mt.setAccessible(true);mt.set(activity, null);Method mtm = ContextThemeWrapper.class.getDeclaredMethod("initializeTheme",new Class[0]);mtm.setAccessible(true);mtm.invoke(activity, new Object[0]);Method mCreateTheme = AssetManager.class.getDeclaredMethod("createTheme", new Class[0]);mCreateTheme.setAccessible(true);Object internalTheme = mCreateTheme.invoke(newAssetManager, new Object[0]);Field mTheme = Resources.Theme.class.getDeclaredField("mTheme");mTheme.setAccessible(true);mTheme.set(theme, internalTheme);} catch (Throwable e) {Log.e("InstantRun","Failed to update existing theme for activity "+ activity, e);}pruneResourceCaches(resources);}}Collection> references;if (Build.VERSION.SDK_INT >= 19) {Class resourcesManagerClass = Class.forName("android.app.ResourcesManager");Method mGetInstance = resourcesManagerClass.getDeclaredMethod("getInstance", new Class[0]);mGetInstance.setAccessible(true);Object resourcesManager = mGetInstance.invoke(null,new Object[0]);try {Field fMActiveResources = resourcesManagerClass.getDeclaredField("mActiveResources");fMActiveResources.setAccessible(true);ArrayMap> arrayMap = (ArrayMap) fMActiveResources.get(resourcesManager);references = arrayMap.values();} catch (NoSuchFieldException ignore) {Field mResourceReferences = resourcesManagerClass.getDeclaredField("mResourceReferences");mResourceReferences.setAccessible(true);references = (Collection) mResourceReferences.get(resourcesManager);}} else {Class activityThread = Class.forName("android.app.ActivityThread");Field fMActiveResources = activityThread.getDeclaredField("mActiveResources");fMActiveResources.setAccessible(true);Object thread = getActivityThread(context, activityThread);HashMap> map = (HashMap) fMActiveResources.get(thread);references = map.values();}for (WeakReference wr : references) {Resources resources = (Resources) wr.get();if (resources != null) {try {Field mAssets = Resources.class.getDeclaredField("mAssets");mAssets.setAccessible(true);mAssets.set(resources, newAssetManager);} catch (Throwable ignore) {Field mResourcesImpl = Resources.class.getDeclaredField("mResourcesImpl");mResourcesImpl.setAccessible(true);Object resourceImpl = mResourcesImpl.get(resources);Field implAssets = resourceImpl.getClass().getDeclaredField("mAssets");implAssets.setAccessible(true);implAssets.set(resourceImpl, newAssetManager);}resources.updateConfiguration(resources.getConfiguration(),resources.getDisplayMetrics());}}} catch (Throwable e) {throw new IllegalStateException(e);}}

说明：该方法的作用是替换所有当前app的mAssets为newAssetManager。
monkeyPatchExistingResources的流程如下：
1.如果resource.ap_文件有改变，那么新建一个AssetManager对象newAssetManager，然后用newAssetManager对象替换所有当前Resource、Resource.Theme的mAssets成员变量。
2.如果当前的已经有Activity启动了，还需要替换所有Activity中mAssets成员变量

判断Server是否已经启动，如果没有启动，则启动Server。然后调用realApplication的onCreate方法代理realApplication的生命周期。

接下来我们分析下Server负责的热部署、温部署和冷部署等问题。

Server热部署、温部署和冷部署

首先重点关注一下Server的内部类SocketServerReplyThread。

SocketServerReplyThread

private class SocketServerReplyThread extends Thread {private final LocalSocket mSocket;SocketServerReplyThread(LocalSocket socket) {this.mSocket = socket;}public void run() {try {DataInputStream input = new DataInputStream(this.mSocket.getInputStream());DataOutputStream output = new DataOutputStream(this.mSocket.getOutputStream());try {handle(input, output);} finally {try {input.close();} catch (IOException ignore) {}try {output.close();} catch (IOException ignore) {}}return;} catch (IOException e) {if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Fatal error receiving messages", e);}}}private void handle(DataInputStream input, DataOutputStream output)throws IOException {long magic = input.readLong();if (magic != 890269988L) {Log.w("InstantRun","Unrecognized header format " + Long.toHexString(magic));return;}int version = input.readInt();output.writeInt(4);if (version != 4) {Log.w("InstantRun","Mismatched protocol versions; app is using version 4 and tool is using version "+ version);} else {int message;for (;;) {message = input.readInt();switch (message) {case 7:if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Received EOF from the IDE");}return;case 2:boolean active = Restarter.getForegroundActivity(Server.this.mApplication) != null;output.writeBoolean(active);if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun","Received Ping message from the IDE; returned active = "+ active);}break;case 3:String path = input.readUTF();long size = FileManager.getFileSize(path);output.writeLong(size);if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Received path-exists(" + path+ ") from the " + "IDE; returned size="+ size);}break;case 4:long begin = System.currentTimeMillis();path = input.readUTF();byte[] checksum = FileManager.getCheckSum(path);if (checksum != null) {output.writeInt(checksum.length);output.write(checksum);if (Log.isLoggable("InstantRun", 2)) {long end = System.currentTimeMillis();String hash = new BigInteger(1, checksum).toString(16);Log.v("InstantRun", "Received checksum(" + path+ ") from the " + "IDE: took "+ (end - begin) + "ms to compute "+ hash);}} else {output.writeInt(0);if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Received checksum(" + path+ ") from the "+ "IDE: returning ");}}break;case 5:if (!authenticate(input)) {return;}Activity activity = Restarter.getForegroundActivity(Server.this.mApplication);if (activity != null) {if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun","Restarting activity per user request");}Restarter.restartActivityOnUiThread(activity);}break;case 1:if (!authenticate(input)) {return;}List changes = ApplicationPatch.read(input);if (changes != null) {boolean hasResources = Server.hasResources(changes);int updateMode = input.readInt();updateMode = Server.this.handlePatches(changes,hasResources, updateMode);boolean showToast = input.readBoolean();output.writeBoolean(true);Server.this.restart(updateMode, hasResources,showToast);}break;case 6:String text = input.readUTF();Activity foreground = Restarter.getForegroundActivity(Server.this.mApplication);if (foreground != null) {Restarter.showToast(foreground, text);} else if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun","Couldn't show toast (no activity) : "+ text);}break;}}}}}

说明：socket开启后，开始读取数据，当读到1时，获取代码变化的ApplicationPatch列表，然后调用handlePatches来处理代码的变化。

handlePatches

private int handlePatches(List changes,boolean hasResources, int updateMode) {if (hasResources) {FileManager.startUpdate();}for (ApplicationPatch change : changes) {String path = change.getPath();if (path.endsWith(".dex")) {handleColdSwapPatch(change);boolean canHotSwap = false;for (ApplicationPatch c : changes) {if (c.getPath().equals("classes.dex.3")) {canHotSwap = true;break;}}if (!canHotSwap) {updateMode = 3;}} else if (path.equals("classes.dex.3")) {updateMode = handleHotSwapPatch(updateMode, change);} else if (isResourcePath(path)) {updateMode = handleResourcePatch(updateMode, change, path);}}if (hasResources) {FileManager.finishUpdate(true);}return updateMode;}

说明：本方法主要通过判断Change的内容，来判断采用什么模式（热部署、温部署或冷部署）

• 如果后缀为“.dex”,冷部署处理handleColdSwapPatch
• 如果后缀为“classes.dex.3”,热部署处理handleHotSwapPatch
• 其他情况,温部署，处理资源handleResourcePatch

handleColdSwapPatch冷部署

private static void handleColdSwapPatch(ApplicationPatch patch) {if (patch.path.startsWith("slice-")) {File file = FileManager.writeDexShard(patch.getBytes(), patch.path);if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Received dex shard " + file);}}}

说明：该方法把dex文件写到私有目录，等待整个app重启，重启之后，使用前面提到的IncrementalClassLoader加载dex即可。

handleHotSwapPatch热部署

private int handleHotSwapPatch(int updateMode, ApplicationPatch patch) {if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Received incremental code patch");}try {String dexFile = FileManager.writeTempDexFile(patch.getBytes());if (dexFile == null) {Log.e("InstantRun", "No file to write the code to");return updateMode;}if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Reading live code from " + dexFile);}String nativeLibraryPath = FileManager.getNativeLibraryFolder().getPath();DexClassLoader dexClassLoader = new DexClassLoader(dexFile,this.mApplication.getCacheDir().getPath(),nativeLibraryPath, getClass().getClassLoader());Class aClass = Class.forName("com.android.tools.fd.runtime.AppPatchesLoaderImpl", true,dexClassLoader);try {if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Got the patcher class " + aClass);}PatchesLoader loader = (PatchesLoader) aClass.newInstance();if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Got the patcher instance " + loader);}String[] getPatchedClasses = (String[]) aClass.getDeclaredMethod("getPatchedClasses", new Class[0]).invoke(loader, new Object[0]);if (Log.isLoggable("InstantRun", 2)) {Log.v("InstantRun", "Got the list of classes ");for (String getPatchedClass : getPatchedClasses) {Log.v("InstantRun", "class " + getPatchedClass);}}if (!loader.load()) {updateMode = 3;}} catch (Exception e) {Log.e("InstantRun", "Couldn't apply code changes", e);e.printStackTrace();updateMode = 3;}} catch (Throwable e) {Log.e("InstantRun", "Couldn't apply code changes", e);updateMode = 3;}return updateMode;}

说明：该方法将patch的dex文件写入到临时目录，然后使用DexClassLoader去加载dex。然后反射调用AppPatchesLoaderImpl类的load方法。
需要强调的是：AppPatchesLoaderImpl继承自抽象类AbstractPatchesLoaderImpl，并实现了抽象方法：getPatchedClasses。而AbstractPatchesLoaderImpl抽象类代码如下：

public abstract class AbstractPatchesLoaderImpl implements PatchesLoader {public abstract String[] getPatchedClasses();public boolean load() {try {for (String className : getPatchedClasses()) {ClassLoader cl = getClass().getClassLoader();Class aClass = cl.loadClass(className + "$override");Object o = aClass.newInstance();Class originalClass = cl.loadClass(className);Field changeField = originalClass.getDeclaredField("$change");changeField.setAccessible(true);Object previous = changeField.get(null);if (previous != null) {Field isObsolete = previous.getClass().getDeclaredField("$obsolete");if (isObsolete != null) {isObsolete.set(null, Boolean.valueOf(true));}}changeField.set(null, o);if ((Log.logging != null)&& (Log.logging.isLoggable(Level.FINE))) {Log.logging.log(Level.FINE, String.format("patched %s",new Object[] { className }));}}} catch (Exception e) {if (Log.logging != null) {Log.logging.log(Level.SEVERE, String.format("Exception while patching %s",new Object[] { "foo.bar" }), e);}return false;}return true;}}

Instant Run热部署原理

由上面的代码分析，我们对Instant Run的流程可以分析如下：

1，在第一次构建apk时，在每一个类中注入了一个$change的成员变量，它实现了IncrementalChange接口，并在每一个方法中，插入了一段类似的逻辑。

IncrementalChange localIncrementalChange = $change;if (localIncrementalChange != null) {localIncrementalChange.access$dispatch("onCreate.(Landroid/os/Bundle;)V", new Object[] { this,... });return;}

当$change不为空的时候，执行IncrementalChange方法。

2，当我们修改代码中方法的实现之后，点击InstantRun，它会生成对应的patch文件来记录你修改的内容。patch文件中的替换类是在所修改类名的后面追加$override，并实现IncrementalChange接口。

3，生成AppPatchesLoaderImpl类，继承自AbstractPatchesLoaderImpl，并实现getPatchedClasses方法，来记录哪些类被修改了。

4，调用load方法之后，根据getPatchedClasses返回的修改过的类的列表，去加载对应的override类，然后把原有类的change设置为对应的实现了IncrementalChange接口的$override类。

Instant Run运行机制总结

Instant Run运行机制主要涉及到热部署、温部署和冷部署，主要是在第一次运行，app运行时期，有代码修改时。

第一次编译

1.把Instant-Run.jar和instant-Run-bootstrap.jar打包到主dex中
2.替换AndroidManifest.xml中的application配置
3.使用asm工具，在每个类中添加$change，在每个方法前加逻辑
4.把源代码编译成dex，然后存放到压缩包instant-run.zip中

app运行时

1.获取更改后资源resource.ap_的路径
2.设置ClassLoader。setupClassLoader：
使用IncrementalClassLoader加载apk的代码，将原有的BootClassLoader → PathClassLoader改为BootClassLoader → IncrementalClassLoader → PathClassLoader继承关系。
3.createRealApplication：
创建apk真实的application
4.monkeyPatchApplication
反射替换ActivityThread中的各种Application成员变量
5.monkeyPatchExistingResource
反射替换所有存在的AssetManager对象
6.调用realApplication的onCreate方法
7.启动Server，Socket接收patch列表

有代码修改时

1.生成对应的$override类
2.生成AppPatchesLoaderImpl类，记录修改的类列表
3.打包成patch，通过socket传递给app
4.app的server接收到patch之后，分别按照handleColdSwapPatch、handleHotSwapPatch、handleResourcePatch等待对patch进行处理
5.restart使patch生效

在Android插件化、Android热修复、apk加壳/脱壳中借鉴了Instant Run运行机制，所以理解Instant Run运行机制对于向更深层次的研究是很有帮助的，对于我们自己书写框架也是有借鉴意义的。