add Provider 启动原理

blogs/Android/Framework/Interview/其他应用组件相关/Provider 启动原理.md

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+---
+Provider 的启动原理
+---
+
+1. 了解 ContentProvider 的生命周期
+2. 熟悉 ContentProvider 的启动流程
+3. 熟悉 Provider 启动过程中各方通信原理
+
+```java
+ContextResolver resolver = context.getContentResolver();
+resolver.insert(uri, contentValues);
+public ContextResolver getContextResolver(){
+    return mContextResolver;
+}
+private ContextImpl(ConntextImpl container, ...) {
+    mContextResolver = new ApplicationContextResolver(this, ...);
+} 
+public final Uri insert(Uri url, ContentValues values) {
+    IContentProvider provider = acquireProvider(url);
+    Uri createdRow = provider.insert(mPackageName, url, values);
+    return createdRow;
+}
+protected IContentProvider acquireProvider(Context context, String auth) {
+    return mMainThread.acquireProvider(context, ...);
+}
+IContentProvider acquireProvider(Context c, String auth, ...){
+    IContentProvider provider = acquireExistingProvider(c, ...);
+    if(provider != null){
+        return provider;
+    }
+    IActivityManager.ContentProviderHolder holder = null;
+    holder = ActivityManagerNative.getDefault().getContentProvider(getApplicationThread(), auth, userId, stable);
+    holder = installProvider(c, holder, holder.info, ...);
+    return holder.provider;
+}
+```
+
+获取 ContentProvider 的过程小结：
+
+本地找 IContentProvider 对象 -> 找到直接返回，不然请求 AMS  -> AMS 返回 holder，本地安装。
+
+本地找：
+
+```java
+IContentProvider acquireExistingProvider (Context c, ...) {
+	final ProviderKey key = new ProviderKey(auth, userId);
+    final ProviderClientRecord pr = mProviderMap.get(key);
+    if(pr == null){
+        return null;
+    }
+    IContentProvider provider = pr.mProvider;
+    IBinder jBinder = provider.asBinder();
+    if(!jBinder.isBinderAlive()) {
+        handleUnstableProvideDiedLocked(jBinder, true);
+        return null;
+    }
+    return provider;
+}
+```
+
+远程找：
+
+```java
+ContentProviderHolder getContentProvider(IApplicationThread caller, ...) {
+	return getContentProviderImpl(caller, name, null, ...);
+}
+ContentProviderHolder getContentProviderImpl(IApplicationThread caller, ...) {
+    // 如果 ContentProviderRecord 存在就直接返回
+    // ContentProviderRecord 不存在，就创建一个
+    // 如果 ContentProviderRecord 能跑在调用者进程，就直接返回，否则往下走
+    // 如果 provider 所在进程没启动，就启动进程，然后等待发布，完成的时候返回
+    // 如果 binder 对象还没发布就请求发布，然后等待，完成的时候返回
+    
+    if(providerRunning){
+        // provider 存在
+    }
+    if(!providerRunning){
+        // provider 不存在
+    }
+    synchronized(cpr){
+        while(cpr.provider == null){
+            cpr.wait();
+        }
+    }
+    return cpr!=null?cpr.newHolder(conn):null;
+}
+```
+
+```java
+if(providerRunning){
+	cpi = cpr.info;
+	if(r!=null&&cpr.canRunHere(r)){
+		ContentProviderHolder holder = cpr.newHolder(null);
+		holder.provider = null;
+		return holder;
+	}
+    conn = incProviderCountLocked(r, cpr, token, stable);
+    return cpr.newHolder(conn);
+}
+```
+
+```java
+// 应用端安装 provider
+IActivityManager.ContentProviderHolder installProvider(Context context, ...) {
+	Context c = context.createPackageContext(ai.packageName, ...);
+    ContentProvider localProvider = cl.loadClass(info.name).newInstance();
+    IContentProvider provider = localProvider.getIContentProvider();
+    // 调用 provider#onCreate
+    localProvider.attachInfo(c, info);
+    
+    ProviderClientRecord pr = mLocalProvidersByName.get(cname);
+    holder = new IActivityManager.ContentProviderHolder(info);
+    holder.provider = provider;
+    pr = installProviderAuthoritiesLocked(provider, localProvider, holder);
+    mLocalProviders.put(jBinder, pr);
+    mLocalProvidersByName.put(cname, pr);
+    return pr.mHolder;
+}
+```
+
+provider 不存在的情况：
+
+```java
+if(!providerRunning) {
+	cpr = new ContentProviderRecord(this, cpi, ai, comp, singleton);
+    if(r!=null&&cpr.canRunHere(r)){
+        return cpr.newHolder(null);
+    }
+    if(i>=N){
+        ProcessRecord proc = getProcessRecordLocked(...);
+        if(proc!=null&&proc.thread!=null){
+            proc.thread.scheduleInstallProvider(cpi);
+        }else{
+            proc = startProcessLocked(cpi.processName, ...);
+        }
+        mLaunchingProviders.add(cpr);
+    }
+}
+```
+
+应用启动时主动发布 provider 的 Binder 对象：
+
+```java
+boolean attachApplicationLocked(IApplicationThread thread, ...){
+    List<ProviderInfo> providers = generateApplicationProvidersLocked(app);
+    if(providers != null && checkAppInLaunchingProvidersLocked(app)){
+        Message msg = mHandler.obtainMessage(CONTENT_PROVIDER_PUBLISH_TIMEOUT_MSG);
+        msg.obj = app;
+        mHandler.sendMessageDelayed(msg, CONTENT_PROVIDER_PUBLISH_TIMEOUT);
+    }
+    // 让应用端初始化 provider
+    thread.bindApplication(processName, appInfo, providers, ...);
+    return true;
+}
+// 应用主线程执行
+private void handleBindApplication(AppBindData data){
+    List<ProviderInfo> provider = data.providers;
+    if(providers != null){
+        installContentProviders(app, providers);
+    }
+}
+void installContentProviders(Context context, List<ProviderInfo> providers){
+    List<ContentProviderHolder> results = new ArrayList<ContentProviderHolder>();
+    for(ProviderInfo cpi: providers){
+        ContentProviderHolder cph = installProvider(context, ...);
+        results.add(cph);
+    }
+    AMP.publishContentProviders(getApplicationThread(), results);
+}
+void publishContentProviders(IApplicationThread caller, providers){
+    final ProcessRecord r = getRecordForAppLocked(caller);
+    for(int i=0;i<N;i++){
+        ContentProviderHolder src = providers.get(i);
+        ContentProviderRecord dst = r.pubProviders.get(src.info.name);
+        
+        // 更新 provider 缓存
+        // 更新 mLaunchingProviders
+        // 删除超时计时的消息
+        
+        synchronized(dst){
+            dst.provider = src.provider;
+            dst.proc = r;
+            dst.notifyAll();
+        }
+    }
+}
+```
+
+AMS 主动向应用请求发布 provider：
+
+```java
+public void scheduleInstallProvider(ProviderInfo provider){
+    sendMessage(H.INSTALL_PROVIDER, provider);
+}
+public void handleInstallProvider(ProviderInfo info){
+    installContentProviders(mInitialApplication, Lists.newArrayList(info));
+}
+```
+
+#### 总结
+
+Provider 进程未启动：
+
+![](https://i.loli.net/2020/03/25/8SMpsqbDTO5u7YL.png)
+
+Provider 进程已经启动：
+
+![](https://i.loli.net/2020/03/25/nYjFePh2gRbkQ1X.png)
+