Android之本程序ContentProvider啟動流程分析（1）

1、ContentProvider介紹

ContentProvider主要用于向外部提供資料

1、自己應用程序提供資料

2、其它app程序的提供資料

這裡分析本程序的ContentProvider的啟動過程

2、ContentProvider啟動分析

1、我們知道Android程式入口在ActivityThread.java檔案的main函數裡面，如下代碼

public static void main(String[] args) {
        Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain");
        SamplingProfilerIntegration.start();
 
        // CloseGuard defaults to true and can be quite spammy.  We
        // disable it here, but selectively enable it later (via
        // StrictMode) on debug builds, but using DropBox, not logs.
        CloseGuard.setEnabled(false);
 
        Environment.initForCurrentUser();
 
        // Set the reporter for event logging in libcore
        EventLogger.setReporter(new EventLoggingReporter());
 
        AndroidKeyStoreProvider.install();
 
        // Make sure TrustedCertificateStore looks in the right place for CA certificates
        final File configDir = Environment.getUserConfigDirectory(UserHandle.myUserId());
        TrustedCertificateStore.setDefaultUserDirectory(configDir);
 
        Process.setArgV0("<pre-initialized>");
 
        Looper.prepareMainLooper();
 
        ActivityThread thread = new ActivityThread();
        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();
 
        throw new RuntimeException("Main thread loop unexpectedly exited");
    }      

2、我們這裡可以看到有關鍵函數thread.attach(false)方法，我們跟蹤進去，attach部分方法如下

private void attach(boolean system) {
        sCurrentActivityThread = this;
        mSystemThread = system;
        if (!system) {
            ViewRootImpl.addFirstDrawHandler(new Runnable() {
                @Override
                public void run() {
                    ensureJitEnabled();
                }
            });
            android.ddm.DdmHandleAppName.setAppName("<pre-initialized>",
                                                    UserHandle.myUserId());
            RuntimeInit.setApplicationObject(mAppThread.asBinder());
            final IActivityManager mgr = ActivityManagerNative.getDefault();
            try {
                mgr.attachApplication(mAppThread);
            } catch (RemoteException ex) {
                // Ignore
            }
            // Watch for getting close to heap limit.
            BinderInternal.addGcWatcher(new Runnable() {
                @Override public void run() {
                    if (!mSomeActivitiesChanged) {
                        return;
                    }
                    Runtime runtime = Runtime.getRuntime();
                    long dalvikMax = runtime.maxMemory();
                    long dalvikUsed = runtime.totalMemory() - runtime.freeMemory();
                    if (dalvikUsed > ((3*dalvikMax)/4)) {
                        if (DEBUG_MEMORY_TRIM) Slog.d(TAG, "Dalvik max=" + (dalvikMax/1024)
                                + " total=" + (runtime.totalMemory()/1024)
                                + " used=" + (dalvikUsed/1024));
                        mSomeActivitiesChanged = false;
                        try {
                            mgr.releaseSomeActivities(mAppThread);
                        } catch (RemoteException e) {
                        }
                    }
                }
            });
*******      

3、這裡有個關鍵方法，mgr.attachApplication(mAppThread)，我們看下這個方法ActivityManagerService.java檔案裡面的實作

@Override
    public final void attachApplication(IApplicationThread thread) {
        synchronized (this) {
            int callingPid = Binder.getCallingPid();
            final long origId = Binder.clearCallingIdentity();
            attachApplicationLocked(thread, callingPid);
            Binder.restoreCallingIdentity(origId);
        }
    }      

4、我們再看關鍵函數attachApplicationLocked函數部分實作

private final boolean attachApplicationLocked(IApplicationThread thread,
            int pid) {
        *******
        boolean normalMode = mProcessesReady || isAllowedWhileBooting(app.info);
        List<ProviderInfo> providers = normalMode ? generateApplicationProvidersLocked(app) : null;
 
        *******
            thread.bindApplication(processName, appInfo, providers, app.instrumentationClass,
                    profilerInfo, app.instrumentationArguments, app.instrumentationWatcher,
                    app.instrumentationUiAutomationConnection, testMode, enableOpenGlTrace,
                    isRestrictedBackupMode || !normalMode, app.persistent,
                    new Configuration(mConfiguration), app.compat,
                    getCommonServicesLocked(app.isolated),
                    mCoreSettingsObserver.getCoreSettingsLocked());
            updateLruProcessLocked(app, false, null);
            app.lastRequestedGc = app.lastLowMemory = SystemClock.uptimeMillis();      

5、這裡又調用了generateApplicationProvidersLocked(app)函數，這個函數傳回了一個ProviderInfo對象的集合，我們跟蹤這個函數看是如何得到這個集合的。

private final List<ProviderInfo> generateApplicationProvidersLocked(ProcessRecord app) {
        List<ProviderInfo> providers = null;
        try {
            ParceledListSlice<ProviderInfo> slice = AppGlobals.getPackageManager().
                queryContentProviders(app.processName, app.uid,
                        STOCK_PM_FLAGS | PackageManager.GET_URI_PERMISSION_PATTERNS);
            providers = slice != null ? slice.getList() : null;
        } catch (RemoteException ex) {
        }
        if (DEBUG_MU) Slog.v(TAG_MU,
                "generateApplicationProvidersLocked, app.info.uid = " + app.uid);
        int userId = app.userId;
        if (providers != null) {
            int N = providers.size();
            app.pubProviders.ensureCapacity(N + app.pubProviders.size());
            for (int i=0; i<N; i++) {
                ProviderInfo cpi =
                    (ProviderInfo)providers.get(i);
                boolean singleton = isSingleton(cpi.processName, cpi.applicationInfo,
                        cpi.name, cpi.flags);
                if (singleton && UserHandle.getUserId(app.uid) != UserHandle.USER_OWNER) {
                    providers.remove(i);
                    N--;
                    i--;
                    continue;
                }
 
                ComponentName comp = new ComponentName(cpi.packageName, cpi.name);
                ContentProviderRecord cpr = mProviderMap.getProviderByClass(comp, userId);
                if (cpr == null) {
                    cpr = new ContentProviderRecord(this, cpi, app.info, comp, singleton);
                    mProviderMap.putProviderByClass(comp, cpr);
                }
                if (DEBUG_MU) Slog.v(TAG_MU,
                        "generateApplicationProvidersLocked, cpi.uid = " + cpr.uid);
                app.pubProviders.put(cpi.name, cpr);
                if (!cpi.multiprocess || !"android".equals(cpi.packageName)) {
                    app.addPackage(cpi.applicationInfo.packageName, cpi.applicationInfo.versionCode,
                            mProcessStats);
                }
                ensurePackageDexOpt(cpi.applicationInfo.packageName);
            }
        }
        return providers;
    }      

這裡很明顯是查詢ContentProvider通過app程序名字和app的uid,然後得到一個ProviderInfo的集合，就是這裡的providers,然後我們周遊這個集合，通過每個ProviderInfo的packageName和name屬性建構ComponentName這個對象，然後再去建構ContentProviderRecord對象，key為ComponentName,value為ContentProviderRecord添加到這個ProviderMap對象裡面，也就是這行代碼

mProviderMap.putProviderByClass(comp, cpr);

然後把傳回的providers作為參數，傳遞給了bindApplication函數。