本文參考Android应用程序组件Content Provider的启动过程源码分析http://blog.csdn.net/luoshengyang/article/details/6963418和《Android系统源码情景分析》，作者罗升阳。
0、总图流程图例如以下：
1、MainActivity进程向ActivityServiceManager主线程发送GET_CONTENT_PORVIDER_TRANSACTION
例如以下图：
如图：第一步
~/Android/frameworks/base/core/java/android/app
----ActivityManagerNative.java
class ActivityManagerProxy implements IActivityManager
{
......
public ContentProviderHolder getContentProvider(IApplicationThread caller,
String name) throws RemoteException
{
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(caller != null ? caller.asBinder() : null);
data.writeString(name);
mRemote.transact(GET_CONTENT_PROVIDER_TRANSACTION, data, reply, 0);
reply.readException();
int res = reply.readInt();
ContentProviderHolder cph = null;
if (res != 0) {
cph = ContentProviderHolder.CREATOR.createFromParcel(reply);
}
data.recycle();
reply.recycle();
return cph;
}
......
}当中name为shy.luo.providers.articles。
如图：第二步，省略binder_transaction传输过程，由于上面已经分析过了。
如图：第三步
~/Android/frameworks/base/core/java/android/app
----ActivityManagerNative.java
public abstract class ActivityManagerNative extends Binder implements IActivityManager
{
......
public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
throws RemoteException {
switch (code) {
case GET_CONTENT_PROVIDER_TRANSACTION: {
data.enforceInterface(IActivityManager.descriptor);
IBinder b = data.readStrongBinder();
IApplicationThread app = ApplicationThreadNative.asInterface(b);
String name = data.readString();
ContentProviderHolder cph = getContentProvider(app, name);
reply.writeNoException();
if (cph != null) {
reply.writeInt(1);
cph.writeToParcel(reply, 0);
} else {
reply.writeInt(0);
}
return true;
}
.......
} 当中name为shy.luo.providers.articles。如图：第四步
～/Android/frameworks/base/services/java/com/android/server/am
----ActivityManagerService.java
public final class ActivityManagerService extends ActivityManagerNative
implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
......
public final ContentProviderHolder getContentProvider(
IApplicationThread caller, String name) {
......
return getContentProviderImpl(caller, name);
}
......
}
它调用getContentProviderImpl函数来进一步运行操作。
public final class ActivityManagerService extends ActivityManagerNative
implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
......
private final ContentProviderHolder getContentProviderImpl(
IApplicationThread caller, String name) {
ContentProviderRecord cpr;
ProviderInfo cpi = null;
synchronized(this) {
ProcessRecord r = null;
if (caller != null) {
r = getRecordForAppLocked(caller);
......
}
// First check if this content provider has been published...
cpr = mProvidersByName.get(name);
if (cpr != null) {
......
} else {
try {
cpi = AppGlobals.getPackageManager().
resolveContentProvider(name,
STOCK_PM_FLAGS | PackageManager.GET_URI_PERMISSION_PATTERNS);
} catch (RemoteException ex) {
}
......
}
cpr = mProvidersByClass.get(cpi.name);
final boolean firstClass = cpr == null;
if (firstClass) {
try {
ApplicationInfo ai =
AppGlobals.getPackageManager().
getApplicationInfo(
cpi.applicationInfo.packageName,
STOCK_PM_FLAGS);
......
cpr = new ContentProviderRecord(cpi, ai);
} catch (RemoteException ex) {
// pm is in same process, this will never happen.
}
}
if (r != null && cpr.canRunHere(r)) {
// If this is a multiprocess provider, then just return its
// info and allow the caller to instantiate it. Only do
// this if the provider is the same user as the caller's
// process, or can run as root (so can be in any process).
return cpr;
}
......
// This is single process, and our app is now connecting to it.
// See if we are already in the process of launching this
// provider.
final int N = mLaunchingProviders.size();
int i;
for (i=0; i<N; i++) {
if (mLaunchingProviders.get(i) == cpr) {
break;
}
}
// If the provider is not already being launched, then get it
// started.
if (i >= N) {
final long origId = Binder.clearCallingIdentity();
ProcessRecord proc = startProcessLocked(cpi.processName,
cpr.appInfo, false, 0, "content provider",
new ComponentName(cpi.applicationInfo.packageName,
cpi.name), false);
......
mLaunchingProviders.add(cpr);
......
}
// Make sure the provider is published (the same provider class
// may be published under multiple names).
if (firstClass) {
mProvidersByClass.put(cpi.name, cpr);
}
cpr.launchingApp = proc;
mProvidersByName.put(name, cpr);
......
}
// Wait for the provider to be published...
synchronized (cpr) {
while (cpr.provider == null) {
......
try {
cpr.wait();
} catch (InterruptedException ex) {
}
}
}
return cpr;
}
......
} 主要做了下面几件事：
（1）依据传递过来的name创建了ProviderInfo对象和ApplicationInfo对象，然后依据它们两个对象创建了ContentProviderRecord对象。
（2）创建了ProcessRecord对象，并创建ArticlesProvider子线程。
（3）循环等待cpr.provider的值不为null。
2、创建ArticlesProvider子线程，略。
3、ArticlesProvider子线程向ActivityManagerService子线程发送ATTACH_APPLICATION_TRANSACTION
第一、二、三步所有省略。仅仅看第四步。
～/Android/frameworks/base/services/java/com/android/server/am
----ActivityManagerService.java
public final class ActivityManagerService extends ActivityManagerNative
implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
......
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
// Find the application record that is being attached... either via
// the pid if we are running in multiple processes, or just pull the
// next app record if we are emulating process with anonymous threads.
ProcessRecord app;
if (pid != MY_PID && pid >= 0) {
synchronized (mPidsSelfLocked) {
app = mPidsSelfLocked.get(pid);
}
} else if (mStartingProcesses.size() > 0) {
......
} else {
......
}
......
app.thread = thread;
app.curAdj = app.setAdj = -100;
app.curSchedGroup = Process.THREAD_GROUP_DEFAULT;
app.setSchedGroup = Process.THREAD_GROUP_BG_NONINTERACTIVE;
app.forcingToForeground = null;
app.foregroundServices = false;
app.debugging = false;
......
boolean normalMode = mProcessesReady || isAllowedWhileBooting(app.info);
List providers = normalMode ? generateApplicationProvidersLocked(app) : null;
try {
......
thread.bindApplication(processName, app.instrumentationInfo != null
? app.instrumentationInfo : app.info, providers,
app.instrumentationClass, app.instrumentationProfileFile,
app.instrumentationArguments, app.instrumentationWatcher, testMode,
isRestrictedBackupMode || !normalMode,
mConfiguration, getCommonServicesLocked());
......
} catch (Exception e) {
......
}
......
return true;
}
......
private final List generateApplicationProvidersLocked(ProcessRecord app) {
List providers = null;
try {
providers = AppGlobals.getPackageManager().
queryContentProviders(app.processName, app.info.uid,
STOCK_PM_FLAGS | PackageManager.GET_URI_PERMISSION_PATTERNS);
} catch (RemoteException ex) {
}
if (providers != null) {
final int N = providers.size();
for (int i=0; i<N; i++) {
ProviderInfo cpi =
(ProviderInfo)providers.get(i);
ContentProviderRecord cpr = mProvidersByClass.get(cpi.name);
if (cpr == null) {
cpr = new ContentProviderRecord(cpi, app.info);
mProvidersByClass.put(cpi.name, cpr);
}
app.pubProviders.put(cpi.name, cpr);
app.addPackage(cpi.applicationInfo.packageName);
ensurePackageDexOpt(cpi.applicationInfo.packageName);
}
}
return providers;
}
......
}
主要做了下面几件事：
（1）获取了刚在ActivityServiceManager主线程创建的ProcessRecord对象。
（2）依据这个ProcessRecord对象获得刚在ActivityServiceManager主线程中的ProviderInfo对象。
（3）ActivityServiceManager子线程向ArticlesProvider子线程发送BIND_APPLICATION_TRANSACTION。
4、ActivityServiceManager子线程向ArticlesProvider子线程发送BIND_APPLICATION_TRANSACTION
如图：第一步
~/Android/frameworks/base/core/java/android/app
----ApplicationThreadNative.java。ApplicationThreadProxy类
public final void bindApplication(String packageName, ApplicationInfo info,
List<ProviderInfo> providers, ComponentName testName,
String profileName, Bundle testArgs, IInstrumentationWatcher testWatcher, int debugMode,
boolean restrictedBackupMode, Configuration config,
Map<String, IBinder> services) throws RemoteException {
Parcel data = Parcel.obtain();
data.writeInterfaceToken(IApplicationThread.descriptor);
data.writeString(packageName);
info.writeToParcel(data, 0);
data.writeTypedList(providers);
if (testName == null) {
data.writeInt(0);
} else {
data.writeInt(1);
testName.writeToParcel(data, 0);
}
data.writeString(profileName);
data.writeBundle(testArgs);
data.writeStrongInterface(testWatcher);
data.writeInt(debugMode);
data.writeInt(restrictedBackupMode ? 1 : 0);
config.writeToParcel(data, 0);
data.writeMap(services);
mRemote.transact(BIND_APPLICATION_TRANSACTION, data, null,
IBinder.FLAG_ONEWAY);
data.recycle();
}
当中providers是在ActivityServiceManager主线程依据传递过来的name创建了ProviderInfo对象。
如图：第二步，省略binder_transaction传输过程，由于上面已经分析过了。
如图：第三步
~/Android/frameworks/base/core/java/android/app
----ApplicationThreadNative.java
public abstract class ApplicationThreadNative extends Binder
implements IApplicationThread {
........
public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
throws RemoteException {
switch (code) {
case BIND_APPLICATION_TRANSACTION:
{
data.enforceInterface(IApplicationThread.descriptor);
String packageName = data.readString();
ApplicationInfo info =
ApplicationInfo.CREATOR.createFromParcel(data);
List<ProviderInfo> providers =
data.createTypedArrayList(ProviderInfo.CREATOR);
ComponentName testName = (data.readInt() != 0)
? new ComponentName(data) : null;
String profileName = data.readString();
Bundle testArgs = data.readBundle();
IBinder binder = data.readStrongBinder();
IInstrumentationWatcher testWatcher = IInstrumentationWatcher.Stub.asInterface(binder);
int testMode = data.readInt();
boolean restrictedBackupMode = (data.readInt() != 0);
Configuration config = Configuration.CREATOR.createFromParcel(data);
HashMap<String, IBinder> services = data.readHashMap(null);
bindApplication(packageName, info,
providers, testName, profileName,
testArgs, testWatcher, testMode, restrictedBackupMode,
config, services);
return true;
}
.....
} 当中providers是在ActivityServiceManager主线程依据传递过来的name创建了ProviderInfo对象。
如图：第四步
～/Android/frameworks/base/core/java/android/app
----ActivityThread.java
public final class ActivityThread {
......
private final class ApplicationThread extends ApplicationThreadNative {
......
public final void bindApplication(String processName,
ApplicationInfo appInfo, List<ProviderInfo> providers,
ComponentName instrumentationName, String profileFile,
Bundle instrumentationArgs, IInstrumentationWatcher instrumentationWatcher,
int debugMode, boolean isRestrictedBackupMode, Configuration config,
Map<String, IBinder> services) {
if (services != null) {
// Setup the service cache in the ServiceManager
ServiceManager.initServiceCache(services);
}
AppBindData data = new AppBindData();
data.processName = processName;
data.appInfo = appInfo;
data.providers = providers;
data.instrumentationName = instrumentationName;
data.profileFile = profileFile;
data.instrumentationArgs = instrumentationArgs;
data.instrumentationWatcher = instrumentationWatcher;
data.debugMode = debugMode;
data.restrictedBackupMode = isRestrictedBackupMode;
data.config = config;
queueOrSendMessage(H.BIND_APPLICATION, data);
}
......
}
......
}
这个函数把相关的信息都封装成一个AppBindData对象，然后以一个消息的形式发送到主线程的消息队列中去等等待处理。这个消息终于在ArticlesProvider主线程中处理。
主要做了下面几件事：
（1）依据传递过来的providers把ArticlesProvider这个Content Provider类载入到内存中来了，并调用了它的onCreat方法。
（2）创建了Transport对象，它的关系图例如以下：
（3）ArticlesProvider主线程ActivityServiceManager子线程发送PUBLISH_CONTENT_PROVIDER_TRANSACTION
6、ArticlesProvider主线程ActivityServiceManager子线程发送PUBLISH_CONTENT_PROVIDER_TRANSACTION
第一、二、三步所有省略。仅仅看第四步。
～/Android/frameworks/base/services/java/com/android/server/am
----ActivityManagerService.java
public final class ActivityManagerService extends ActivityManagerNative
implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
......
public final void publishContentProviders(IApplicationThread caller,
List<ContentProviderHolder> providers) {
......
synchronized(this) {
final ProcessRecord r = getRecordForAppLocked(caller);
......
final int N = providers.size();
for (int i=0; i<N; i++) {
ContentProviderHolder src = providers.get(i);
if (src == null || src.info == null || src.provider == null) {
continue;
}
ContentProviderRecord dst = r.pubProviders.get(src.info.name);
if (dst != null) {
mProvidersByClass.put(dst.info.name, dst);
String names[] = dst.info.authority.split(";");
for (int j = 0; j < names.length; j++) {
mProvidersByName.put(names[j], dst);
}
int NL = mLaunchingProviders.size();
int j;
for (j=0; j<NL; j++) {
if (mLaunchingProviders.get(j) == dst) {
mLaunchingProviders.remove(j);
j--;
NL--;
}
}
synchronized (dst) {
dst.provider = src.provider;
dst.app = r;
dst.notifyAll();
}
......
}
}
}
}
......
} 还记得ActivityServiceManager在循环等待么？这里dst.provider = src.provider，为ContentProviderProxy对象（实现了IContentProvider）。
之后调用notifyAll通知ActivityManagerService主线程，让它从等待中返回。
7、notifyAll通知ActivityManagerService主线程
8、ActivityManagerService主线程向MainActivity进程发送返回结果
~/Android/frameworks/base/core/java/android/app
----ActivityThread.java
private final IContentProvider getProvider(Context context, String name) {
IContentProvider existing = getExistingProvider(context, name);
if (existing != null) {
return existing;
}
IActivityManager.ContentProviderHolder holder = null;
try {
holder = ActivityManagerNative.getDefault().getContentProvider(
getApplicationThread(), name);
} catch (RemoteException ex) {
}
IContentProvider prov = installProvider(context, holder.provider,
holder.info, true);
......
return prov;
}public class ArticlesAdapter {
......
private ContentResolver resolver = null;
public ArticlesAdapter(Context context) {
resolver = context.getContentResolver();
}
......
public int getArticleCount() {
int count = 0;
try {
IContentProvider provider = resolver.acquireProvider(Articles.CONTENT_URI);
Bundle bundle = provider.call(Articles.METHOD_GET_ITEM_COUNT, null, null);
count = bundle.getInt(Articles.KEY_ITEM_COUNT, 0);
} catch(RemoteException e) {
e.printStackTrace();
}
return count;
}
......
}最后返回的是ContentProviderProxy对象，指向了ArticlesProvider主线程中Transport对象。例如以下图：
Bundle bundle = provider.call(Articles.METHOD_GET_ITEM_COUNT, null, null);使用进程间通信的方式取得博客栏目数量。
由于要传输的数据比較小。