Android应用程序组件Content Provider的启动过程源代码分析（3）-白红宇

Step 7. ActivityManagerService.getContentProviderImpl

这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityManagerService.java文件中：

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;

}

......

}

这个函数比较长，我们一步一步地分析。
函数首先是获取调用者的进程记录块信息：

ProcessRecord r = null;  
if (caller != null) {  
    r = getRecordForAppLocked(caller);  
    ......  
}  

在我们这个情景中，要获取的就是应用程序Article的进程记录块信息了，后面会用到。

在ActivityManagerService中，有两个成员变量是用来保存系统中的Content Provider信息的，一个是mProvidersByName，一个是mProvidersByClass，前者是以Content Provider的authoriry值为键值来保存的，后者是以Content Provider的类名为键值来保存的。一个Content Provider可以有多个authority，而只有一个类来和它对应，因此，这里要用两个Map来保存，这里为了方便根据不同条件来快速查找而设计的。下面的代码就是用来检查要获取的Content Provider是否已经加存在的了：

// 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.

}

}

在我们这个情景中，由于是第一次调用ArticlesProvider接口，因此，在mProvidersByName和mProvidersByClass两个Map中都不存在ArticlesProvider的相关信息，因此，这里会通过AppGlobals.getPackageManager函数来获得PackageManagerService服务接口，然后分别通过它的resolveContentProvider和getApplicationInfo函数来分别获取ArticlesProvider应用程序的相关信息，分别保存在cpi和cpr这两个本地变量中。这些信息都是在安装应用程序的过程中保存下来的，具体可以参考

一文。

本文转自 Luoshengyang 51CTO博客，原文链接：http://blog.51cto.com/shyluo/966983，如需转载请自行联系原作者