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Android ContentProvider 初始化过程

Android ContentProvider 初始化过程

作者: 董江鹏 | 来源:发表于2020-05-22 16:57 被阅读0次

由于每次看源码都记不住,每次都要重新梳理一遍,很累,就干脆写成文档,方便后续翻看。
遇到一次由进程初始化超时引发的闪退,调试App的时候动了两下,就闪退了,打印AndroidRuntime,没有信息,说明不是运行时异常,只能抓log看


log_kill.png

log看起来是初始化ContentProvider超时了,我们知道ContentProvider初始化(onCreate)是在Application生命周期方法attachBaseContext之后、onCreate之前,只能去framework的源码中搜索

我们在源码中搜索log中出现的这句timeout publishing content providers
查到log在ActivityManagerService.java里

private final void processContentProviderPublishTimedOutLocked(ProcessRecord app) {
        cleanupAppInLaunchingProvidersLocked(app, true);
        removeProcessLocked(app, false, true, "timeout publishing content providers");
    }

进一步溯源

private final boolean attachApplicationLocked(IApplicationThread thread,int pid) {
                ...
            Message msg = mHandler.obtainMessage(CONTENT_PROVIDER_PUBLISH_TIMEOUT_MSG);
            msg.obj = app;
            mHandler.sendMessageDelayed(msg, CONTENT_PROVIDER_PUBLISH_TIMEOUT);
                ...
            }

再次溯源,到了我们比较熟悉的ActivityThread里

private void attach(boolean system) {
    ...
    final IActivityManager mgr = ActivityManagerNative.getDefault();
            try {
                mgr.attachApplication(mAppThread);
            } catch (RemoteException ex) {
                throw ex.rethrowFromSystemServer();
            }
    ...
}

这时,我们知道,在进程启动的时候会在AMS里发送一个处理超时的消息,正常启动的应用会在某一时刻将这个消息清除掉,而超时则会执行这个消息。
我们接着再看消息是何时被清除的,依然还是在AMS里

public final void publishContentProviders(IApplicationThread caller,List<ContentProviderHolder> providers) {
    ...
    mHandler.removeMessages(CONTENT_PROVIDER_PUBLISH_TIMEOUT_MSG, r);
    ...
}

再次溯源,再次来到ActivityThread里

private void installContentProviders(Context context, List<ProviderInfo> providers) {
    ...
    IActivityManager.ContentProviderHolder cph = installProvider(context, null, cpi,false /*noisy*/, true /*noReleaseNeeded*/, true /*stable*/);
    ...
    try {
            ActivityManagerNative.getDefault().publishContentProviders(getApplicationThread(), results);
        } catch (RemoteException ex) {
            throw ex.rethrowFromSystemServer();
        }
    ...
}

继续溯源,来到我们熟悉的方法

private void handleBindApplication(AppBindData data) {
    ...
    Applicatiohandlen app = data.info.makeApplication(data.restrictedBackupMode, null);
    ...
    installContentProviders(app, data.providers);
    ...
}

这个方法我们知道,在ActivityThread初始化调用attach之后,AMS会回调这个方法。
相当于如果这个方法执行太慢,就会触发AMS的超时保护消息,引发kill。
我们还需要看看我们的代码是如何影响到这个执行时间的,即需要弄清楚Application生命周期方法调用过程。
查看上述handleBindApplication所展示的第一句,data的参数info为LoadedApk,
我们需要进入LoadedApk.java查看

public Application makeApplication(boolean forceDefaultAppClass,Instrumentation instrumentation) {
    ...
    app = mActivityThread.mInstrumentation.newApplication(
                    cl, appClass, appContext);
    ...
}

继续进入Instrumentation.java

 static public Application newApplication(Class<?> clazz, Context context)
            throws InstantiationException, IllegalAccessException, 
            ClassNotFoundException {
        Application app = (Application)clazz.newInstance();
        app.attach(context);
        return app;
    }

这里就是Application类创建时机
进行Application.java

final void attach(Context context) {
        attachBaseContext(context);
        mLoadedApk = ContextImpl.getImpl(context).mPackageInfo;
    }

终于找到了我们最熟悉的attachBaseContext方法。
让我们再找一下ContentProvider的onCreate时机,先回到上述的ActivityThread.java的publishContentProviders方法,可以看到有个
installContentProviders方法在前面执行,查看该方法,

private IActivityManager.ContentProviderHolder installProvider(Context context,IActivityManager.ContentProviderHolder holder, ProviderInfo info,boolean noisy, boolean noReleaseNeeded, boolean stable) {
    ...
    final java.lang.ClassLoader cl = c.getClassLoader();
                localProvider = (ContentProvider)cl.
                    loadClass(info.name).newInstance();
                provider = localProvider.getIContentProvider();
                if (provider == null) {
                    Slog.e(TAG, "Failed to instantiate class " +
                          info.name + " from sourceDir " +
                          info.applicationInfo.sourceDir);
                    return null;
                }
                if (DEBUG_PROVIDER) Slog.v(
                    TAG, "Instantiating local provider " + info.name);
                // XXX Need to create the correct context for this provider.
                localProvider.attachInfo(c, info);
    ...

}

这里从ClassLoader里加载ContentProvider类实例,并调用attachInfo方法,让我们查看ContentProvider.java

private void attachInfo(Context context, ProviderInfo info, boolean testing) {
    ...
    ContentProvider.this.onCreate();
    ...
}

终于找到了我们熟悉的ContentProvider生命周期方法。

小结

小结一下,我们的应用和ContentProvider初始化过程大致为:
ActivityThread.attath()->
AMS.attachApplication()->
sendMessage(CONTENT_PROVIDER_PUBLISH_TIMEOUT_MSG)->
ActivityThread.handleBindApplication()->
Application.attachBaseContext()->
ActivityThread.installContentProviders->
ContentProvider.onCreate()->
AMS.publishContentProviders()->
removeMessage(CONTENT_PROVIDER_PUBLISH_TIMEOUT_MSG)->
Application.onCreate()

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