query方法到AMS的调用
在上述文章中我用到了Content Provider查询数据库的例子如下：
private void query() {
Cursor cursor = this.getContentResolver().query(mCurrentURI, null, null, null, null); //1
showlog("count=" + cursor.getCount());
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
String table = cursor.getString(cursor.getColumnIndex("table_name"));
String name = cursor.getString(cursor.getColumnIndex("name"));
String detail = cursor.getString(cursor.getColumnIndex("detail"));
showlog("table_name:" + table);
showlog("name: " + name);
showlog("detail: " + detail);
cursor.moveToNext();
}
cursor.close();
}
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
ContextWrapper#getContentResolver()
@Override
public ContentResolver getContentResolver() {
return mBase.getContentResolver();
}
Framework学习（八）Service的启动/绑定过程
这篇文章中我们已经分析了，mBase具体指向就是ContextImpl。
frameworks/base/core/java/android/app/ContextImpl.java
ContextImpl#getContentResolver()
private final ApplicationContentResolver mContentResolver;
...
@Override
public ContentResolver getContentResolver() {
return mContentResolver;
}
上面代码返回了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、delete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。
frameworks/base/core/java/android/content/ContentResolver.java
ContentResolver#query()
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) {
...
}
...
}
注释1处通过acquireUnstableProvider方法返回IContentProvider类型的unstableProvider对象。
注释2处调用unstableProvider的query方法。
先看看注释1的方法吧。
ContentResolver#acquireUnstableProvider()
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
ApplicationContentResolver#acquireUnstableProvider()
@Override
protected IContentProvider acquireUnstableProvider(Context c, String auth) {
return mMainThread.acquireProvider(c,
ContentProvider.getAuthorityWithoutUserId(auth),
resolveUserIdFromAuthority(auth), false);
}
返回了ActivityThread类型的mMainThread对象的acquireProvider方法。
frameworks/base/core/java/android/app/ActivityThread.java
ActivityThread#acquireProvider()
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。
AMS到ActivityThread的调用
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
ActivityManagerService#getContentProvider()
@Override
public final ContentProviderHolder getContentProvider(
IApplicationThread caller, String name, int userId, boolean stable) {
...
return getContentProviderImpl(caller, name, null, stable, userId);
}
ActivityManagerService#getContentProviderImpl()
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");
...
}
...
}
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。
应用程序进程启动过程请参考Framework学习（六）应用程序进程启动过程这篇文章。
ActivityThread启动Provider
frameworks/base/services/core/java/com/android/app/ActivityThread.java
ActivityThread#scheduleInstallProvider()
@Override
public void scheduleInstallProvider(ProviderInfo provider) {
sendMessage(H.INSTALL_PROVIDER, provider);
}
这里的H是ActivityThread的内部类并继承Handler。
ActivityThread.H
private class H extends Handler {
public static final int INSTALL_PROVIDER = 145;
...
public void handleMessage(Message msg) {
if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));
switch (msg.what) {
case INSTALL_PROVIDER:
handleInstallProvider((ProviderInfo) msg.obj);
break;
...
}
ActivityThread#handleInstallProvider()
public void handleInstallProvider(ProviderInfo info) {
final StrictMode.ThreadPolicy oldPolicy = StrictMode.allowThreadDiskWrites();
try {
installContentProviders(mInitialApplication, Lists.newArrayList(info)); //1
} finally {
StrictMode.setThreadPolicy(oldPolicy);
}
}
注释1调用了installContentProviders方法。
ActivityThread#installContentProviders()
private void installContentProviders(
Context context, List<ProviderInfo> providers) {
final ArrayList<IActivityManager.ContentProviderHolder> results =
new ArrayList<IActivityManager.ContentProviderHolder>();
for (ProviderInfo cpi : providers) { //1
if (DEBUG_PROVIDER) {
StringBuilder buf = new StringBuilder(128);
buf.append("Pub ");
buf.append(cpi.authority);
buf.append(": ");
buf.append(cpi.name);
Log.i(TAG, buf.toString());
}
IActivityManager.ContentProviderHolder cph = installProvider(context, null, cpi,
false /*noisy*/, true /*noReleaseNeeded*/, true /*stable*/); //2
if (cph != null) {
cph.noReleaseNeeded = true;
results.add(cph);
}
}
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）。
注释2处调用installProvider方法来启动这些Content Provider。
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。
ActivityThread#installProvider()
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;
}
注释1处通过反射来创建ContentProvider类型的localProvider对象。
注释2处调用了它的attachInfo方法。
frameworks/base/core/java/android/content/ContentProvider.java
ContentProvider#attachInfo()
public void attachInfo(Context context, ProviderInfo info) {
attachInfo(context, info, false);
}
private void attachInfo(Context context, ProviderInfo info, boolean testing) {
mNoPerms = testing;
/*
* Only allow it to be set once, so after the content service gives
* this to us clients can't change it.
*/
if (mContext == null) {
mContext = context;
if (context != null) {
mTransport.mAppOpsManager = (AppOpsManager) context.getSystemService(
Context.APP_OPS_SERVICE);
}
mMyUid = Process.myUid();
if (info != null) {
setReadPermission(info.readPermission);
setWritePermission(info.writePermission);
setPathPermissions(info.pathPermissions);
mExported = info.exported;
mSingleUser = (info.flags & ProviderInfo.FLAG_SINGLE_USER) != 0;
setAuthorities(info.authority);
}
ContentProvider.this.onCreate(); //1
}
}
注释1处调用了ContentProvider的onCreate方法，它是一个抽象方法，具体实现在具体Content Provider中。这样Content Provider就启动完毕了。
原文作者：huaxun66
原文链接：https://blog.csdn.net/huaxun66/article/details/78194820
更多系列教程GitHub白嫖入口：https://github.com/Timdk857/Android-Architecture-knowledge-2-
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