Android系统在新进程中启动自定义服务过程(startService)的原理分析

??? s.info = info; ???

??? queueOrSendMessage(H.CREATE_SERVICE, s); ??? } ???

??? ...... ??? ??? } ???

??? ...... ??? ??? }

这里调用ActivityThread的queueOrSendMessage将一个CreateServiceData数据放到消息队列中去，并且分开这个消息。注意，这里已经是在上面Step 4创建的新进程中执行了。

Step 14. ActivityThread.queueOrSendMessage

这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中：

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??? public final class ActivityThread { ??? ??? ...... ???

??? private final void queueOrSendMessage(int what, Object obj) { ??? queueOrSendMessage(what, obj, 0, 0); ??? } ???

??? private final void queueOrSendMessage(int what, Object obj, int arg1, int arg2) {

??? synchronized (this) { ??? ......

??? Message msg = Message.obtain(); ??? msg.what = what; ??? msg.obj = obj; ??? msg.arg1 = arg1; ??? msg.arg2 = arg2; ??? mH.sendMessage(msg); ??? } ??? }

???

??? ...... ??? ??? }

这里调用成员变量mH的sendMessage函数进行消息分发。这里的mH的类型为H，它继承于Handler类。

Step 15. H.sendMessage 这个函数继承于

Handle

类的

sendMessage

函数中，定义在

frameworks/base/core/java/android/os/Handler.java文件中。这个函数我们就不看了，有兴趣的读者可以自己研究一下。消息分发以后，就进入到H.handleMessage函数进行处理了。 Step 16. H.handleMessage

这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中：

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??? public final class ActivityThread { ??? ??? ...... ???

??? private final class H extends Handler { ??? ??? ...... ???

??? public void handleMessage(Message msg) { ???

??? ...... ???

??? switch (msg.what) { ???

??? ...... ???

??? case CREATE_SERVICE:

??? handleCreateService((CreateServiceData)msg.obj); ??? break; ???

??? ...... ??? } ???

??? ...... ???

??? } ???

??? ...... ??? ??? } ???

??? ...... ??? ??? }

这里要处理的消息是CREATE_SERVICE，它调用ActivityThread类的handleCreateService成员函数进一步处理。

Step 17. ActivityThread.handleCreateService

这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中：

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??? public final class ActivityThread { ??? ??? ...... ???

??? private final void handleCreateService(CreateServiceData data) {

??? // If we are getting ready to gc after going to the background, well ??? // we are back active so skip it. ??? unscheduleGcIdler(); ???

??? LoadedApk packageInfo = getPackageInfoNoCheck( ??? data.info.applicationInfo); ??? Service service = null; ??? try {

??? java.lang.ClassLoader cl = packageInfo.getClassLoader(); ??? service = (Service) cl.loadClass(data.info.name).newInstance(); ??? } catch (Exception e) {

??? if (!mInstrumentation.onException(service, e)) { ??? throw new RuntimeException(

??? \ + data.info.name ??? + \ + e.toString(), e); ??? }

??? } ???

??? try {

??? if (localLOGV) Slog.v(TAG, \ + data.info.name); ???

??? ContextImpl context = new ContextImpl(); ??? context.init(packageInfo, null, this); ???

??? Application mInstrumentation);

??? context.setOuterContext(service);

??? service.attach(context, this, data.info.name, data.token, app, ??? ActivityManagerNative.getDefault()); ??? service.onCreate();

??? mServices.put(data.token, service); ??? try {

??? ActivityManagerNative.getDefault().serviceDoneExecuting( ??? data.token, 0, 0, 0); ??? } catch (RemoteException e) { ??? // nothing to do. ??? } ???

??? } catch (Exception e) {

??? if (!mInstrumentation.onException(service, e)) { ??? throw new RuntimeException(

??? \ + data.info.name ??? + \ + e.toString(), e); ??? } ??? } ??? } ???

??? ...... ??? ??? }

app

=

packageInfo.makeApplication(false,

这里的data.info.name就是自定义的服务类shy.luo.ashmem.Server了。

Step 18. ClassLoader.loadClass

这一步实现在上面的ActivityThread.handleCreateService函数中：

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