Android深入四大组件(九)Content Provider的启动过程
前言
Content Provider做为四大组件之一,通常情况下并没有其他的组件使用频繁,但这不能作为我们不去深入学习它的理由。关于Content Provider一篇文章是写不完的,这一篇文章先来介绍它的启动过程。
1.query方法到AMS的调用过程
在Android IPC机制(四)用ContentProvider进行进程间通信这篇文章我举了一个Content Provider使用的例子,在Activity中我是使用如下代码调用Content Provider的:
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
public class ContentProviderActivity extends AppCompatActivity { private final static String TAG = "ContentProviderActivity"; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_content_provider); Uri uri = Uri.parse("content://com.example.liuwangshu.mooncontentprovide.GameProvider"); ContentValues mContentValues = new ContentValues(); mContentValues.put("_id", 2); mContentValues.put("name", "大航海时代ol"); mContentValues.put("describe", "最好玩的航海网游"); getContentResolver().insert(uri, mContentValues);//1 Cursor gameCursor = getContentResolver().query(uri, new String[]{"name", "describe"}, null, null, null); ... } }
要想调用Content Provider,首先需要使用注释1处的getContentResolver方法,如下所示。
frameworks/base/core/Java/android/content/ContextWrapper.java
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
@Override public ContentResolver getContentResolver() { return mBase.getContentResolver(); }
这里mBase指的是ContextImpl,ContextImpl的getContentResolver方法如下所示。
frameworks/base/core/java/android/app/ContextImpl.java
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
@Override public ContentResolver getContentResolver() { return mContentResolver; }
上面的代码return了ApplicationContentResolver类型的mContentResolver对象,ApplicationContentResolver是ContextImpl中的静态内部类,继承自ContentResolver,它在ContextImpl的构造方法中被创建。
当我们调用ContentResolver的insert、query、update等方法时就会启动Content Provider,这里拿query方法来进行举例。
query方法的实现在ApplicationContentResolver的父类ContentResolver中,代码如下所示。
frameworks/base/core/java/android/content/ContentResolver.java
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
public final @Nullable Cursor query(final @RequiresPermission.Read @NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder, @Nullable CancellationSignal cancellationSignal) { Preconditions.checkNotNull(uri, "uri"); IContentProvider unstableProvider = acquireUnstableProvider(uri);//1 ... try { ... try { qCursor = unstableProvider.query(mPackageName, uri, projection, selection, selectionArgs, sortOrder, remoteCancellationSignal);//2 } catch (DeadObjectException e) { ... } ... }
在注释1处通过acquireUnstableProvider方法返回IContentProvider类型的unstableProvider对象,在注释2处调用unstableProvider的query方法。我们查看acquireUnstableProvider方法做了什么,如下所示。
frameworks/base/core/java/android/content/ContentResolver.java
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
public final IContentProvider acquireUnstableProvider(Uri uri) { if (!SCHEME_CONTENT.equals(uri.getScheme())) {//1 return null; } String auth = uri.getAuthority(); if (auth != null) { return acquireUnstableProvider(mContext, uri.getAuthority());//2 } return null; }
注释1处用来检查Uri的scheme是否等于”content”,如果不是则返回null。注释2处调用了acquireUnstableProvider方法,这是个抽象方法,它的实现在ContentResolver的子类ApplicationContentResolver中:
frameworks/base/core/java/android/app/ContextImpl.java
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
@Override protected IContentProvider acquireUnstableProvider(Context c, String auth) { return mMainThread.acquireProvider(c, ContentProvider.getAuthorityWithoutUserId(auth), resolveUserIdFromAuthority(auth), false); }
return了ActivityThread类型的mMainThread对象的acquireProvider方法:
frameworks/base/core/java/android/app/ActivityThread.java
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
public final IContentProvider acquireProvider( Context c, String auth, int userId, boolean stable) { final IContentProvider provider = acquireExistingProvider(c, auth, userId, stable);//1 if (provider != null) { return provider; } IActivityManager.ContentProviderHolder holder = null; try { holder = ActivityManagerNative.getDefault().getContentProvider( getApplicationThread(), auth, userId, stable);//2 } catch (RemoteException ex) { throw ex.rethrowFromSystemServer(); } if (holder == null) { Slog.e(TAG, "Failed to find provider info for " + auth); return null; } holder = installProvider(c, holder, holder.info, true /*noisy*/, holder.noReleaseNeeded, stable);//3 return holder.provider; }
注释1处检查ActivityThread中的ArrayMap类型的mProviderMap中是否有目标ContentProvider存在,有则返回,没有就会在注释2处调用AMP的getContentProvider方法,最终会调用AMS的getContentProvider方法。注释3处的installProvider方法用来将注释2处返回的ContentProvider相关的数据存储在mProviderMap中,起到缓存的作用,这样使用相同的Content Provider时,就不需要每次都要调用AMS的getContentProvider方法。使用我们接着查看AMS的getContentProvider方法,代码如下所示。
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
@Override public final ContentProviderHolder getContentProvider( IApplicationThread caller, String name, int userId, boolean stable) { ... return getContentProviderImpl(caller, name, null, stable, userId); }
getContentProvider方法return了getContentProviderImpl方法:
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
private ContentProviderHolder getContentProviderImpl(IApplicationThread caller, String name, IBinder token, boolean stable, int userId) { ... ProcessRecord proc = getProcessRecordLocked( cpi.processName, cpr.appInfo.uid, false);//1 if (proc != null && proc.thread != null && !proc.killed) { ... if (!proc.pubProviders.containsKey(cpi.name)) { checkTime(startTime, "getContentProviderImpl: scheduling install"); proc.pubProviders.put(cpi.name, cpr); try { proc.thread.scheduleInstallProvider(cpi);//2 } catch (RemoteException e) { } } } else { checkTime(startTime, "getContentProviderImpl: before start process"); proc = startProcessLocked(cpi.processName, cpr.appInfo, false, 0, "content provider", new ComponentName(cpi.applicationInfo.packageName, cpi.name), false, false, false);//3 checkTime(startTime, "getContentProviderImpl: after start process"); ... } ... }
getContentProviderImpl方法的代码很多,这里截取了关键的部分。注释1处通过getProcessRecordLocked方法来获取目标ContentProvider的应用程序进程信息,这些信息用ProcessRecord类型的proc来表示,如果该应用进程已经启动就会调用注释2处的代码,否则就会调用注释3的startProcessLocked方法来启动进程。这里我们假设ContentProvider的应用进程还没有启动,关于应用进程启动过程,我在Android应用程序进程启动过程(前篇)已经讲过,最终会调用ActivityThread的main方法,代码如下所示。
frameworks/base/core/java/android/app/ActivityThread.java
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
public static void main(String[] args) { ... Looper.prepareMainLooper();//1 ActivityThread thread = new ActivityThread();//2 thread.attach(false); if (sMainThreadHandler == null) { sMainThreadHandler = thread.getHandler(); } if (false) { Looper.myLooper().setMessageLogging(new LogPrinter(Log.DEBUG, "ActivityThread")); } // End of event ActivityThreadMain. Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER); Looper.loop();//3 throw new RuntimeException("Main thread loop unexpectedly exited"); }
注释1处通过prepareMainLooper方法在ThreadLocal中获取Looper,并在注释3处开启消息循环。在注释2处创建了ActivityThread并调用了它的attach方法:
frameworks/base/core/java/android/app/ActivityThread.java
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
private void attach(boolean system) { ... final IActivityManager mgr = ActivityManagerNative.getDefault();//1 try { mgr.attachApplication(mAppThread);//2 } catch (RemoteException ex) { throw ex.rethrowFromSystemServer(); } ... }
注释1处最终会得到AMS,在注释2处调用AMS的attachApplication方法,并将ApplicationThread类型的mAppThread对象传进去。
query方法到AMS的调用过程,如下面时序图所示(省略应用程序进程启动过程)。
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
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
@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
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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。