image.png
2.AMS启动Content Provider的过程
我们接着来查看AMS的attachApplication方法，如下所示。
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
@Override
public final void attachApplication(IApplicationThread thread) {
synchronized (this) {
int callingPid = Binder.getCallingPid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid);
Binder.restoreCallingIdentity(origId);
}
}
attachApplication方法中又调用了attachApplicationLocked方法：
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
...
thread.bindApplication(processName, appInfo, providers, app.instrumentationClass,
profilerInfo, app.instrumentationArguments, app.instrumentationWatcher,
app.instrumentationUiAutomationConnection, testMode,
mBinderTransactionTrackingEnabled, enableTrackAllocation,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(mConfiguration), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked());
...
}
attachApplicationLocked方法中调用了thread的bindApplication方法，thread是IApplicationThread类型的，从类型名字就可以看出来是用于进程间通信，这里实现bindApplication方法的是ApplicationThreadProxy类，它实现了IApplicationThread接口。
frameworks/base/core/java/android/app/ApplicationThreadNative.java
class ApplicationThreadProxy implements IApplicationThread {
...
@Override
public final void bindApplication(String packageName, ApplicationInfo info,
List<ProviderInfo> providers, ComponentName testName, ProfilerInfo profilerInfo,
Bundle testArgs, IInstrumentationWatcher testWatcher,
IUiAutomationConnection uiAutomationConnection, int debugMode,
boolean enableBinderTracking, boolean trackAllocation, boolean restrictedBackupMode,
boolean persistent, Configuration config, CompatibilityInfo compatInfo,
Map<String, IBinder> services, Bundle coreSettings) throws RemoteException {
...
mRemote.transact(BIND_APPLICATION_TRANSACTION, data, null,
IBinder.FLAG_ONEWAY);
data.recycle();
}
...
}
到目前为止，上面的调用过程还是在AMS进程中执行的，因此，需要通过IBinder类型的mRemote对象向新创建的应用程序进程（目标Content Provider所在的进程）发送BIND_APPLICATION_TRANSACTION类型的通信请求。处理这个通信请求的是在新创建的应用程序进程中执行的ApplicationThread的bindApplication方法，如下所示。
frameworks/base/core/java/android/app/ActivityThread.java
public final void bindApplication(String processName, ApplicationInfo appInfo,
List<ProviderInfo> providers, ComponentName instrumentationName,
ProfilerInfo profilerInfo, Bundle instrumentationArgs,
IInstrumentationWatcher instrumentationWatcher,
IUiAutomationConnection instrumentationUiConnection, int debugMode,
boolean enableBinderTracking, boolean trackAllocation,
boolean isRestrictedBackupMode, boolean persistent, Configuration config,
CompatibilityInfo compatInfo, Map<String, IBinder> services, Bundle coreSettings) {
...
sendMessage(H.BIND_APPLICATION, data);
}
调用sendMessage方法像H发送BIND_APPLICATION类型消息，H的handleMessage方法如下所示。
frameworks/base/core/java/android/app/ActivityThread.java
public void handleMessage(Message msg) {
if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));
switch (msg.what) {
...
case BIND_APPLICATION:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "bindApplication");
AppBindData data = (AppBindData)msg.obj;
handleBindApplication(data);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
...
}
...
}
我们接着查看handleBindApplication方法：
frameworks/base/core/java/android/app/ActivityThread.java
private void handleBindApplication(AppBindData data) {
...
final ContextImpl appContext = ContextImpl.createAppContext(this, data.info);//1
try {
final ClassLoader cl = instrContext.getClassLoader();
mInstrumentation = (Instrumentation)
cl.loadClass(data.instrumentationName.getClassName()).newInstance();//2
} catch (Exception e) {
...
}
final ComponentName component = new ComponentName(ii.packageName, ii.name);
mInstrumentation.init(this, instrContext, appContext, component,
data.instrumentationWatcher, data.instrumentationUiAutomationConnection);//3
...
Application app = data.info.makeApplication(data.restrictedBackupMode, null);//4
mInitialApplication = app;
if (!data.restrictedBackupMode) {
if (!ArrayUtils.isEmpty(data.providers)) {
installContentProviders(app, data.providers);//5
mH.sendEmptyMessageDelayed(H.ENABLE_JIT, 10*1000);
}
}
...
mInstrumentation.callApplicationOnCreate(app);//6
...
}
handleBindApplication方法的代码很长，这里截取了主要的部分。注释1处创建了ContextImpl 。注释2处通过反射创建Instrumentation并在注释3处初始化Instrumentation。注释4处创建Application并且在注释6处调用Application的onCreate方法，这意味着Content Provider所在的应用程序进程已经启动完毕，在这之前，注释5处调用installContentProviders方法来启动Content Provider，代码如下所示。
frameworks/base/core/java/android/app/ActivityThread.java
private void installContentProviders(
Context context, List<ProviderInfo> providers) {
final ArrayList<IActivityManager.ContentProviderHolder> results =
new ArrayList<IActivityManager.ContentProviderHolder>();
for (ProviderInfo cpi : providers) {//1
...
IActivityManager.ContentProviderHolder cph = installProvider(context, null, cpi,
false /*noisy*/, true /*noReleaseNeeded*/, true /*stable*/);//2
...
}
try {
ActivityManagerNative.getDefault().publishContentProviders(
getApplicationThread(), results);//3
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
注释1处遍历当前应用程序进程的ProviderInfo列表，得到每个Content Provider的ProviderInfo（存储Content Provider的信息），并在注释2处调用installProvider方法来启动这些Content Provider。在注释3处通过AMS的publishContentProviders方法将这些Content Provider存储在AMS的mProviderMap中，这个mProviderMap在前面提到过，起到缓存的作用，防止每次使用相同的Content Provider时都会调用AMS的getContentProvider方法。来查看installProvider方法时如何启动Content Provider的，installProvider方法如下所示。
frameworks/base/core/java/android/app/ActivityThread.java
private IActivityManager.ContentProviderHolder installProvider(Context context,
IActivityManager.ContentProviderHolder holder, ProviderInfo info,
boolean noisy, boolean noReleaseNeeded, boolean stable) {
ContentProvider localProvider = null;
...
final java.lang.ClassLoader cl = c.getClassLoader();
localProvider = (ContentProvider)cl.
loadClass(info.name).newInstance();//1
provider = localProvider.getIContentProvider();
if (provider == null) {
...
return null;
}
if (DEBUG_PROVIDER) Slog.v(
TAG, "Instantiating local provider " + info.name);
localProvider.attachInfo(c, info);//2
} catch (java.lang.Exception e) {
...
}
return null;
}
}
...
return retHolder;
}
在注释1处通过反射来创建ContentProvider类型的localProvider对象，并在注释2处调用了它的attachInfo方法：
frameworks/base/core/java/android/content/ContentProvider.java
private void attachInfo(Context context, ProviderInfo info, boolean testing) {
...
ContentProvider.this.onCreate();
}
}
在attachInfo方法中调用了onCreate方法，它是一个抽象方法。这样Content Provider就启动完毕。
最后给出AMS启动Content Provider的时序图。
image.png
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