我想在最开始再废一些周章,来把启动的过程略微的阐述一下,为的就是接下去描述插件化痛点的时候,你会更加的身临其境。
activity的启动过程如下:
- Launcher是系统的apk,点击界面图标会调用相应的Activity.startActivity,或者是直接从ActivityA启动ActivityB
- contextImpl.startActivity()->Instrumentation.executeActivity()
- ActivityManagerNative.getDefault().startActivity()->AMS.startActivity
Instrumentation通过aidl进行跨进程通信,最终调用AMS的startActivity方法 - ActivityStarter.startActivityMayWait()->startActivityLocked()->startActivityUnchecked()
- ActivityStack.resumeFocusedStackTopActivityLocked()->resumeTopActivityUncheckedLocked()->resumeTopActivityInnerLocked()
- ActivityStackSupervisor.startSpecificActivityLocked()->realStartActivityLocked()(如果应用还没有启动那么走mService.startProcessLocked方法)
- app.thread.scheduleLaunchActivity()-> sendMessage(H.LAUNCH_ACTIVITY, r)
- H.handleMessage()->handleLaunchActivity()->performLaunchActivity()
如果是初次启动应用,那么我们接着上面的mService.startProcessLocked去看,直接请求Zygote给启动应用fork一个进程出来
- startProcessLocked()(经过几次重载跳转)->
Process.ProcessStartResult startResult = Process.start(entryPoint,
app.processName, uid, uid, gids, debugFlags, mountExternal,
app.info.targetSdkVersion, app.info.seinfo, requiredAbi, instructionSet,
app.info.dataDir, entryPointArgs);
->Process.startViaZygote() 请求Zygote进程为其生成新进程
- 在startViaZygote方法中设置完各种参数之后,最终调用zygoteSendArgsAndGetResult方法,向Zygote发送创建进程的请求。
内部使用socket通信
zygoteSendArgsAndGetResult(openZygoteSocketIfNeeded(abi), argsForZygote)
- Zygote内部的不断循环方法runSelectLoop会接受到这个请求
if (i == 0) {
ZygoteConnection newPeer = acceptCommandPeer(abiList);
peers.add(newPeer);
fds.add(newPeer.getFileDesciptor());
} else {
boolean done = peers.get(i).runOnce();
if (done) {
peers.remove(i);
fds.remove(i);
}
}
先进行包装成ZygoteConnection对象,并将socket的文件标识做保存。然后在下一次的循环中去执行runOnce
- 在runOnce方法中
pid = Zygote.forkAndSpecialize(parsedArgs.uid, parsedArgs.gid, parsedArgs.gids,parsedArgs.debugFlags, rlimits, parsedArgs.mountExternal, parsedArgs.seInfo, parsedArgs.niceName, fdsToClose, parsedArgs.instructionSet,parsedArgs.appDataDir);
通过这个方法去创建进程,实际上就是fork出一个新的虚拟机实例。
- 如果fork成功了,那么返回的pid==0
if (pid == 0) {
// in child
IoUtils.closeQuietly(serverPipeFd);
serverPipeFd = null;
handleChildProc(parsedArgs, descriptors, childPipeFd, newStderr);
// should never get here, the child is expected to either
// throw ZygoteInit.MethodAndArgsCaller or exec().
return true;
} else {
// in parent...pid of < 0 means failure
IoUtils.closeQuietly(childPipeFd);
childPipeFd = null;
return handleParentProc(pid, descriptors, serverPipeFd, parsedArgs);
}
我们接着去执行handleChildProc
- 这里我们做的就是关闭socket通道,并且启动新的进程
private void handleChildProc(Arguments parsedArgs,
FileDescriptor[] descriptors, FileDescriptor pipeFd, PrintStream newStderr)
throws ZygoteInit.MethodAndArgsCaller {
//关闭socket
closeSocket();
ZygoteInit.closeServerSocket();
...
// End of the postFork event.
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
if (parsedArgs.invokeWith != null) {
WrapperInit.execApplication(parsedArgs.invokeWith,
parsedArgs.niceName, parsedArgs.targetSdkVersion,
VMRuntime.getCurrentInstructionSet(),
pipeFd, parsedArgs.remainingArgs);
} else {
//基本走的都是这种启动方式,通过参数,去寻找目标类的main方法并执行
RuntimeInit.zygoteInit(parsedArgs.targetSdkVersion,
parsedArgs.remainingArgs, null /* classLoader */);
}
}
- zygoteInit
public static final void zygoteInit(int targetSdkVersion, String[] argv, ClassLoader classLoader)
throws ZygoteInit.MethodAndArgsCaller {
...
//初始化
commonInit();
//native的初始化
nativeZygoteInit();
//application的初始化
applicationInit(targetSdkVersion, argv, classLoader);
}
主要的就是applicationInit方法,设置虚拟机的堆大小,和虚拟机的sdkversion
VMRuntime.getRuntime().setTargetHeapUtilization(0.75f);
VMRuntime.getRuntime().setTargetSdkVersion(targetSdkVersion);
并且通过反射的方式去触发目标类的main方法
try {
cl = Class.forName(className, true, classLoader);
} catch (ClassNotFoundException ex) {
throw new RuntimeException(
"Missing class when invoking static main " + className,
ex);
}
Method m;
try {
m = cl.getMethod("main", new Class[] { String[].class });
} catch (NoSuchMethodException ex) {
throw new RuntimeException(
"Missing static main on " + className, ex);
} catch (SecurityException ex) {
throw new RuntimeException(
"Problem getting static main on " + className, ex);
}
最终触发,ActivityThread的main方法
对于activity启动的总结
-
activityA启动ActivityB
由contextImp发起的startActivity跳转到instrumentation的executeStartActivity然后交由ActivityStarter做启动准备,分别又经过ActivityStack栈,观察是否有栈顶Activity可以直接用来resume,最终交由ActivityStackSupervisor来realStartActivityLocked,然后通过applicationThread的scheduleLaunchActivity方法发送消息给H的handler,经过处理执行handleLaunchActivity到performLaunchActivity
-
Launcher点击图标启动应用
依然有Activity.startActivity启动应用,直到ActivityStackSupervisor的startSpecificActivityLocked通过启动service的startProcessLocked,这个是AMS的方法,通过Socket通道,请求Zygote系统进程为目标应用分配VM虚拟机。分配成功之后关闭通道,并且通过反射的方式执行目标类的main方法,也就是ActivityThread的main方法。
走进插件化
讲在前面
我们前面废了相当多的周章,来把启动的过程详细的阐述了一下(其实也没有很详细),为的就是接下去阐述痛点的时候,你会更加的身临其境。
本文是基于android7.1的最新源码分析,你会发现google在不断的修改并强化activity的启动过程,它会想方设法的去阻止你进行插件化修改,因为插件化的方式从某些层面来讲,并不利于android的生态发展。所以你会发现这篇插件化讲解中的启动的源码是这样的,而到了那篇就变了个样,实际以最新版本源码为主。
首先,对于插件化,你需要先了解它的模式
插件化干什么
比如说我们的主app相当的巨大,里面集成了大量的模块,我们的app可能有300+mb,那么这个时候客户可能就很不愿意去下载您的app。
我们需要把我们app的主干功能保存下来,放在主app当中,然后将其余的模块功能做成插件的方式,在主app需要使用到的时候再去调用。
这样我们可以做到
- 并行开发,快速迭代
- 模块间解耦
- 按需加载,节省内存
- 动态升级,我们只需要更新插件就可以做到功能更新,而无需更新整个app
碰到的坎
那么很明显了,好处相当多,我们开始准备着手去做了,我们搞了两个apk,一个是主apk,一个是插件apk。我们琢磨着在主apk中去启动插件apk中的activity。但是发现行不通。报了一个平时开发中也会遇到的exception,当你没有将你需要启动的activity在manifest文件中注册的时候就会出现的错误。
Caused by: android.content.ActivityNotFoundException: Unable to find explicit activity class {org.ding.testmulti/org.ding.testmulti.JustTest}; have you declared this activity in your AndroidManifest.xml?
怎么办?我们先通过错误提示定位到出问题的所在地
at android.app.Instrumentation.checkStartActivityResult(Instrumentation.java:1794)
at android.app.Instrumentation.execStartActivity(Instrumentation.java:1512)
前往execStartActivity方法,问题就出在下面这段代码
int result = ActivityManagerNative.getDefault()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mEmbeddedID : null,
requestCode, 0, null, options);
checkStartActivityResult(result, intent);
也就是说跨进程访问的AMS的startActivity返回的result是错误的result,我们经过一番定位最终发现问题出在ActivityStarter的startActivityMayWait方法中,
ResolveInfo rInfo = mSupervisor.resolveIntent(intent, resolvedType, userId);
返回的是空,
ResolveInfo resolveIntent(Intent intent, String resolvedType, int userId, int flags) {
try {
return AppGlobals.getPackageManager().resolveIntent(intent, resolvedType,
PackageManager.MATCH_DEFAULT_ONLY | flags
| ActivityManagerService.STOCK_PM_FLAGS, userId);
} catch (RemoteException e) {
}
return null;
}
最终我们走的PMS的resolveIntent,如果你看过我的应用安装分析的话(Android app安装过程分析(基于Nougat),你应该会了解,在应用安装的过程中,PMS会将Manifest文件中的内容依次读出,并保存在packageInfo当中,以供使用
最终在PMS.java文件中找到resolveIntent方法
@Override
public ResolveInfo resolveIntent(Intent intent, String resolvedType,
int flags, int userId) {
try {
...
final List query = queryIntentActivitiesInternal(intent, resolvedType,
flags, userId);
Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);
final ResolveInfo bestChoice =
chooseBestActivity(intent, resolvedType, flags, query, userId);
return bestChoice;
} finally {
Trace.traceEnd(TRACE_TAG_PACKAGE_MANAGER);
}
}
也就是说queryIntentActivitiesInternal方法返回的列表为空,并没有找到与intent匹配的activity。
当前流行的解决方案
当前失眠流行的插件化代理解决方案有很多,但是基本的原理无外乎如下两类。分别是hookInstrumentation和hookActivityManagerNative,此处的hook我们可以把它理解成狸猫换太子。就是利用我们自己伪造的来骗过系统,从而达到插件化的效果。
hookInstrumention
市面上使用hookInstrumentation方法的是Small框架,在它的ApkBundleLauncher类中的onCreate方法:
@Override
public void onCreate(Application app) {
super.onCreate(app);
Object/*ActivityThread*/ thread;
List providers;
Instrumentation base;
ApkBundleLauncher.InstrumentationWrapper wrapper;
Field f;
// Get activity thread
thread = ReflectAccelerator.getActivityThread(app);
// Replace instrumentation
try {
//拿到当前thread的Instrumentation对象
//我们主要大费周章的把Instrumentation这个对象取出来是为了对其进行保存,要注意,只要是hook了对象,那么除非真的没有必要
//一般都需要对这个对象进行缓存,以防不时之需
f = thread.getClass().getDeclaredField("mInstrumentation");
f.setAccessible(true);
base = (Instrumentation) f.get(thread);
wrapper = new ApkBundleLauncher.InstrumentationWrapper(base);
f.set(thread, wrapper);
} catch (Exception e) {
throw new RuntimeException("Failed to replace instrumentation for thread: " + thread);
}
...
}
我们在InstrumentationWrapper中看到它重写了execStartActivity方法,来进行替换
/** @Override V21+
* Wrap activity from REAL to STUB */
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode, android.os.Bundle options) {
wrapIntent(intent);
return ReflectAccelerator.execStartActivity(mBase,
who, contextThread, token, target, intent, requestCode, options);
}
/** @Override V20-
* Wrap activity from REAL to STUB */
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode) {
wrapIntent(intent);
return ReflectAccelerator.execStartActivity(mBase,
who, contextThread, token, target, intent, requestCode);
}
wrapIntent(intent)
方法包装intent,然后对activity进行替换,将realActivity替换成我们提前在Manifest中注册好的Activity。
在Small的最新版本中,将Activity再替换回来是放在Hook的Handler.CallBack中的(之前是直接走的mInstrumentation的newActivity来进行Activity的复原)
// Inject message handler
try {
f = thread.getClass().getDeclaredField("mH");
f.setAccessible(true);
Handler ah = (Handler) f.get(thread);
f = Handler.class.getDeclaredField("mCallback");
f.setAccessible(true);
f.set(ah, new ApkBundleLauncher.ActivityThreadHandlerCallback());
} catch (Exception e) {
throw new RuntimeException("Failed to replace message handler for thread: " + thread);
}
@Override
public boolean handleMessage(Message msg) {
switch (msg.what) {
case LAUNCH_ACTIVITY:
//在handler收到LAUNCH_ACTIVITY的信号时进行进行替换
redirectActivity(msg);
break;
case CREATE_SERVICE:
ensureServiceClassesLoadable(msg);
break;
default:
break;
}
return false;
}
HookActivityManagerNative
而DroidPlugin使用的是将ActivityManagerNative整个的Hook掉,具体我们见ProxyHool类
public abstract class ProxyHook extends Hook implements InvocationHandler {
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
try {
if (!isEnable()) {
return method.invoke(mOldObj, args);
}
HookedMethodHandler hookedMethodHandler = mHookHandles.getHookedMethodHandler(method);
if (hookedMethodHandler != null) {
return hookedMethodHandler.doHookInner(mOldObj, method, args);
}
return method.invoke(mOldObj, args);
}
......
}
拿出具体的HookedMethodHandler,然后调用其doHookInner方法
public synchronized Object doHookInner(Object receiver, Method method, Object[] args) throws Throwable {
long b = System.currentTimeMillis();
try {
mUseFakedResult = false;
mFakedResult = null;
boolean suc = beforeInvoke(receiver, method, args);
Object invokeResult = null;
if (!suc) {
invokeResult = method.invoke(receiver, args);
}
afterInvoke(receiver, method, args, invokeResult);
if (mUseFakedResult) {
return mFakedResult;
} else {
return invokeResult;
}
} finally {
long time = System.currentTimeMillis() - b;
if (time > 5) {
Log.i(TAG, "doHookInner method(%s.%s) cost %s ms", method.getDeclaringClass().getName(), method.getName(), time);
}
}
}
通过AOP的方式分别在其方法前后进行hook
我们此处替换掉的ActivityManagerNative,就是在IActivityManagerHookHandle中的startActivity类然后我们看他的beforeInvoke方法
@Override
protected boolean beforeInvoke(Object receiver, Method method, Object[] args) throws Throwable {
RunningActivities.beforeStartActivity();
boolean bRet;
if (Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN_MR2) {
bRet = doReplaceIntentForStartActivityAPILow(args);
} else {
bRet = doReplaceIntentForStartActivityAPIHigh(args);
}
if (!bRet) {
setFakedResult(Activity.RESULT_CANCELED);
return true;
}
return super.beforeInvoke(receiver, method, args);
}
doReplaceIntentForStartActivityAPIHigh
这个方法也是将真Activity信息保存,然后用stubActivity来进行替换。
至于再换回来也是用的callBack,实际上DroidPlugin要比Small要更早的使用Hook callBack的方式
PluginCallbackHook.java
@Override
protected void onInstall(ClassLoader classLoader) throws Throwable {
Object target = ActivityThreadCompat.currentActivityThread();
Class ActivityThreadClass = ActivityThreadCompat.activityThreadClass();
/*替换ActivityThread.mH.mCallback,拦截组件调度消息*/
Field mHField = FieldUtils.getField(ActivityThreadClass, "mH");
Handler handler = (Handler) FieldUtils.readField(mHField, target);
Field mCallbackField = FieldUtils.getField(Handler.class, "mCallback");
//*这里读取出旧的callback并处理*/
Object mCallback = FieldUtils.readField(mCallbackField, handler);
if (!PluginCallback.class.isInstance(mCallback)) {
PluginCallback value = mCallback != null ? new PluginCallback(mHostContext, handler, (Handler.Callback) mCallback) : new PluginCallback(mHostContext, handler, null);
value.setEnable(isEnable());
mCallbacks.add(value);
FieldUtils.writeField(mCallbackField, handler, value);
Log.i(TAG, "PluginCallbackHook has installed");
} else {
Log.i(TAG, "PluginCallbackHook has installed,skip");
}
}
PluginCallback.java
private boolean handleLaunchActivity(Message msg) {
try {
Object obj = msg.obj;
Intent stubIntent = (Intent) FieldUtils.readField(obj, "intent");
//ActivityInfo activityInfo = (ActivityInfo) FieldUtils.readField(obj, "activityInfo", true);
stubIntent.setExtrasClassLoader(mHostContext.getClassLoader());
Intent targetIntent = stubIntent.getParcelableExtra(Env.EXTRA_TARGET_INTENT);
// 这里多加一个isNotShortcutProxyActivity的判断,因为ShortcutProxyActivity的很特殊,启动它的时候,
// 也会带上一个EXTRA_TARGET_INTENT的数据,就会导致这里误以为是启动插件Activity,所以这里要先做一个判断。
// 之前ShortcutProxyActivity错误复用了key,但是为了兼容,所以这里就先这么判断吧。
if (targetIntent != null && !isShortcutProxyActivity(stubIntent)) {
IPackageManagerHook.fixContextPackageManager(mHostContext);
ComponentName targetComponentName = targetIntent.resolveActivity(mHostContext.getPackageManager());
ActivityInfo targetActivityInfo = PluginManager.getInstance().getActivityInfo(targetComponentName, 0);
if (targetActivityInfo != null) {
if (targetComponentName != null && targetComponentName.getClassName().startsWith(".")) {
targetIntent.setClassName(targetComponentName.getPackageName(), targetComponentName.getPackageName() + targetComponentName.getClassName());
}
ResolveInfo resolveInfo = mHostContext.getPackageManager().resolveActivity(stubIntent, 0);
ActivityInfo stubActivityInfo = resolveInfo != null ? resolveInfo.activityInfo : null;
if (stubActivityInfo != null) {
PluginManager.getInstance().reportMyProcessName(stubActivityInfo.processName, targetActivityInfo.processName, targetActivityInfo.packageName);
}
PluginProcessManager.preLoadApk(mHostContext, targetActivityInfo);
ClassLoader pluginClassLoader = PluginProcessManager.getPluginClassLoader(targetComponentName.getPackageName());
setIntentClassLoader(targetIntent, pluginClassLoader);
setIntentClassLoader(stubIntent, pluginClassLoader);
...
Log.i(TAG, "handleLaunchActivity OK");
} else {
Log.e(TAG, "handleLaunchActivity oldInfo==null");
}
} else {
Log.e(TAG, "handleLaunchActivity targetIntent==null");
}
} catch (Exception e) {
Log.e(TAG, "handleLaunchActivity FAIL", e);
}
if (mCallback != null) {
return mCallback.handleMessage(msg);
} else {
return false;
}
}
至此两种最经典的插件化方式分析完毕,之后我们再来看框架的具体使用心得
TBC。。