Android系統在啟動的過程中，會啟動一個應用程序管理服務PackageManagerService，這個服務負責掃描系統中特定的目錄，找到里面的應用程序文件，即以Apk為后綴的文件，然后對這些文件進解析，得到應用程序的相關信息，完成應用程序的安裝過程，本文將詳細分析這個過程。
應用程序管理服務PackageManagerService安裝應用程序的過程，其實就是解析析應用程序配置文件AndroidManifest.xml的過程，并從里面得到得到應用程序的相關信息，例如得到應用程序的組件Activity、Service、Broadcast Receiver和Content Provider等信息，有了這些信息后，通過ActivityManagerService這個服務，我們就可以在系統中正常地使用這些應用程序了。
應用程序管理服務PackageManagerService是系統啟動的時候由SystemServer組件啟動的，啟后它就會執行應用程序安裝的過程，因此，本文將從SystemServer啟動PackageManagerService服務的過程開始分析系統中的應用程序安裝的過程。
應用程序管理服務PackageManagerService從啟動到安裝應用程序的過程如下圖所示：
下面我們具體分析每一個步驟。
Step 1. SystemServer.main
這個函數定義在frameworks/base/services/java/com/android/server/SystemServer.java文件中：
public class SystemServer
{
......
native public static void init1(String[] args);
......
public static void main(String[] args) {
......
init1(args);
......
}
......
} SystemServer組件是由Zygote進程負責啟動的，啟動的時候就會調用它的main函數，這個函數主要調用了JNI方法init1來做一些系統初始化的工作。
Step 2. SystemServer.init1
這個函數是一個JNI方法，實現在 frameworks/base/services/jni/com_android_server_SystemServer.cpp文件中：
namespace android {
extern "C" int system_init();
static void android_server_SystemServer_init1(JNIEnv* env, jobject clazz)
{
system_init();
}
/*
* JNI registration.
*/
static JNINativeMethod gMethods[] = {
/* name, signature, funcPtr */
{ "init1", "([Ljava/lang/String;)V", (void*) android_server_SystemServer_init1 },
};
int register_android_server_SystemServer(JNIEnv* env)
{
return jniRegisterNativeMethods(env, "com/android/server/SystemServer",
gMethods, NELEM(gMethods));
}
}; // namespace android
這個函數很簡單，只是調用了system_init函數來進一步執行操作。
Step 3. libsystem_server.system_init
函數system_init實現在libsystem_server庫中，源代碼位于frameworks/base/cmds/system_server/library/system_init.cpp文件中：
extern "C" status_t system_init()
{
LOGI("Entered system_init()");
sp<ProcessState> proc(ProcessState::self());
sp<IServiceManager> sm = defaultServiceManager();
LOGI("ServiceManager: %p\n", sm.get());
sp<GrimReaper> grim = new GrimReaper();
sm->asBinder()->linkToDeath(grim, grim.get(), 0);
char propBuf[PROPERTY_VALUE_MAX];
property_get("system_init.startsurfaceflinger", propBuf, "1");
if (strcmp(propBuf, "1") == 0) {
// Start the SurfaceFlinger
SurfaceFlinger::instantiate();
}
// Start the sensor service
SensorService::instantiate();
// On the simulator, audioflinger et al don't get started the
// same way as on the device, and we need to start them here
if (!proc->supportsProcesses()) {
// Start the AudioFlinger
AudioFlinger::instantiate();
// Start the media playback service
MediaPlayerService::instantiate();
// Start the camera service
CameraService::instantiate();
// Start the audio policy service
AudioPolicyService::instantiate();
}
// And now start the Android runtime. We have to do this bit
// of nastiness because the Android runtime initialization requires
// some of the core system services to already be started.
// All other servers should just start the Android runtime at
// the beginning of their processes's main(), before calling
// the init function.
LOGI("System server: starting Android runtime.\n");
AndroidRuntime* runtime = AndroidRuntime::getRuntime();
LOGI("System server: starting Android services.\n");
runtime->callStatic("com/android/server/SystemServer", "init2");
// If running in our own process, just go into the thread
// pool. Otherwise, call the initialization finished
// func to let this process continue its initilization.
if (proc->supportsProcesses()) {
LOGI("System server: entering thread pool.\n");
ProcessState::self()->startThreadPool();
IPCThreadState::self()->joinThreadPool();
LOGI("System server: exiting thread pool.\n");
}
return NO_ERROR;
} 這個函數首先會初始化SurfaceFlinger、SensorService、AudioFlinger、MediaPlayerService、CameraService和AudioPolicyService這幾個服務，然后就通過系統全局唯一的AndroidRuntime實例變量runtime的callStatic來調用SystemServer的init2函數了。關于這個AndroidRuntime實例變量runtime的相關資料，可能參考前面一篇文章
Android應用程序進程啟動過程的源代碼分析一文。
Step 4. AndroidRuntime.callStatic
這個函數定義在frameworks/base/core/jni/AndroidRuntime.cpp文件中：
/*
* Call a static Java Programming Language function that takes no arguments and returns void.
*/
status_t AndroidRuntime::callStatic(const char* className, const char* methodName)
{
JNIEnv* env;
jclass clazz;
jmethodID methodId;
env = getJNIEnv();
if (env == NULL)
return UNKNOWN_ERROR;
clazz = findClass(env, className);
if (clazz == NULL) {
LOGE("ERROR: could not find class '%s'\n", className);
return UNKNOWN_ERROR;
}
methodId = env->GetStaticMethodID(clazz, methodName, "()V");
if (methodId == NULL) {
LOGE("ERROR: could not find method %s.%s\n", className, methodName);
return UNKNOWN_ERROR;
}
env->CallStaticVoidMethod(clazz, methodId);
return NO_ERROR;
} 這個函數調用由參數className指定的java類的靜態成員函數，這個靜態成員函數是由參數methodName指定的。上面傳進來的參數className的值為"com/android/server/SystemServer"，而參數methodName的值為"init2"，因此，接下來就會調用SystemServer類的init2函數了。
Step 5. SystemServer.init2
這個函數定義在frameworks/base/services/java/com/android/server/SystemServer.java文件中：
public class SystemServer
{
......
public static final void init2() {
Slog.i(TAG, "Entered the Android system server!");
Thread thr = new ServerThread();
thr.setName("android.server.ServerThread");
thr.start();
}
} 這個函數創建了一個ServerThread線程，PackageManagerService服務就是這個線程中啟動的了。這里調用了ServerThread實例thr的start函數之后，下面就會執行這個實例的run函數了。
Step 6. ServerThread.run
這個函數定義在frameworks/base/services/java/com/android/server/SystemServer.java文件中：
class ServerThread extends Thread {
......
@Override
public void run() {
......
IPackageManager pm = null;
......
// Critical services...
try {
......
Slog.i(TAG, "Package Manager");
pm = PackageManagerService.main(context,
factoryTest != SystemServer.FACTORY_TEST_OFF);
......
} catch (RuntimeException e) {
Slog.e("System", "Failure starting core service", e);
}
......
}
......
} 這個函數除了啟動PackageManagerService服務之外，還啟動了其它很多的服務，例如在前面學習Activity和Service的幾篇文章中經常看到的ActivityManagerService服務，有興趣的讀者可以自己研究一下。
Step 7. PackageManagerService.main
這個函數定義在frameworks/base/services/java/com/android/server/PackageManagerService.java文件中：
class PackageManagerService extends IPackageManager.Stub {
......
public static final IPackageManager main(Context context, boolean factoryTest) {
PackageManagerService m = new PackageManagerService(context, factoryTest);
ServiceManager.addService("package", m);
return m;
}
......
} 這個函數創建了一個PackageManagerService服務實例，然后把這個服務添加到ServiceManager中去，ServiceManager是Android系統Binder進程間通信機制的守護進程，負責管理系統中的Binder對象，具體可以參考
淺談Service Manager成為Android進程間通信（IPC）機制Binder守護進程之路一文。
在創建這個PackageManagerService服務實例時，會在PackageManagerService類的構造函數中開始執行安裝應用程序的過程：
class PackageManagerService extends IPackageManager.Stub {
......
public PackageManagerService(Context context, boolean factoryTest) {
......
synchronized (mInstallLock) {
synchronized (mPackages) {
......
File dataDir = Environment.getDataDirectory();
mAppDataDir = new File(dataDir, "data");
mSecureAppDataDir = new File(dataDir, "secure/data");
mDrmAppPrivateInstallDir = new File(dataDir, "app-private");
......
mFrameworkDir = new File(Environment.getRootDirectory(), "framework");
mDalvikCacheDir = new File(dataDir, "dalvik-cache");
......
// Find base frameworks (resource packages without code).
mFrameworkInstallObserver = new AppDirObserver(
mFrameworkDir.getPath(), OBSERVER_EVENTS, true);
mFrameworkInstallObserver.startWatching();
scanDirLI(mFrameworkDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR,
scanMode | SCAN_NO_DEX, 0);
// Collect all system packages.
mSystemAppDir = new File(Environment.getRootDirectory(), "app");
mSystemInstallObserver = new AppDirObserver(
mSystemAppDir.getPath(), OBSERVER_EVENTS, true);
mSystemInstallObserver.startWatching();
scanDirLI(mSystemAppDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR, scanMode, 0);
// Collect all vendor packages.
mVendorAppDir = new File("/vendor/app");
mVendorInstallObserver = new AppDirObserver(
mVendorAppDir.getPath(), OBSERVER_EVENTS, true);
mVendorInstallObserver.startWatching();
scanDirLI(mVendorAppDir, PackageParser.PARSE_IS_SYSTEM
| PackageParser.PARSE_IS_SYSTEM_DIR, scanMode, 0);
mAppInstallObserver = new AppDirObserver(
mAppInstallDir.getPath(), OBSERVER_EVENTS, false);
mAppInstallObserver.startWatching();
scanDirLI(mAppInstallDir, 0, scanMode, 0);
mDrmAppInstallObserver = new AppDirObserver(
mDrmAppPrivateInstallDir.getPath(), OBSERVER_EVENTS, false);
mDrmAppInstallObserver.startWatching();
scanDirLI(mDrmAppPrivateInstallDir, PackageParser.PARSE_FORWARD_LOCK,
scanMode, 0);
......
}
}
}
......
} 這里會調用scanDirLI函數來掃描移動設備上的下面這五個目錄中的Apk文件：
/system/framework
/system/app
/vendor/app
/data/app
/data/app-private
Step 8. PackageManagerService.scanDirLI
這個函數定義在frameworks/base/services/java/com/android/server/PackageManagerService.java文件中：
class PackageManagerService extends IPackageManager.Stub {
......
private void scanDirLI(File dir, int flags, int scanMode, long currentTime) {
String[] files = dir.list();
......
int i;
for (i=0; i<files.length; i++) {
File file = new File(dir, files[i]);
if (!isPackageFilename(files[i])) {
// Ignore entries which are not apk's
continue;
}
PackageParser.Package pkg = scanPackageLI(file,
flags|PackageParser.PARSE_MUST_BE_APK, scanMode, currentTime);
// Don't mess around with apps in system partition.
if (pkg == null && (flags & PackageParser.PARSE_IS_SYSTEM) == 0 &&
mLastScanError == PackageManager.INSTALL_FAILED_INVALID_APK) {
// Delete the apk
Slog.w(TAG, "Cleaning up failed install of " + file);
file.delete();
}
}
}
......
} 對于目錄中的每一個文件，如果是以后Apk作為后綴名，那么就調用scanPackageLI函數來對它進行解析和安裝。
Step 9. PackageManagerService.scanPackageLI
這個函數定義在frameworks/base/services/java/com/android/server/PackageManagerService.java文件中：
class PackageManagerService extends IPackageManager.Stub {
......
private PackageParser.Package scanPackageLI(File scanFile,
int parseFlags, int scanMode, long currentTime) {
......
String scanPath = scanFile.getPath();
parseFlags |= mDefParseFlags;
PackageParser pp = new PackageParser(scanPath);
......
final PackageParser.Package pkg = pp.parsePackage(scanFile,
scanPath, mMetrics, parseFlags);
......
return scanPackageLI(pkg, parseFlags, scanMode | SCAN_UPDATE_SIGNATURE, currentTime);
}
......
} 這個函數首先會為這個Apk文件創建一個PackageParser實例，接著調用這個實例的parsePackage函數來對這個Apk文件進行解析。這個函數最后還會調用另外一個版本的scanPackageLI函數把來解析后得到的應用程序信息保存在PackageManagerService中。
Step 10. PackageParser.parsePackage
這個函數定義在frameworks/base/core/java/android/content/pm/PackageParser.java文件中：
public class PackageParser {
......
public Package parsePackage(File sourceFile, String destCodePath,
DisplayMetrics metrics, int flags) {
......
mArchiveSourcePath = sourceFile.getPath();
......
XmlResourceParser parser = null;
AssetManager assmgr = null;
boolean assetError = true;
try {
assmgr = new AssetManager();
int cookie = assmgr.addAssetPath(mArchiveSourcePath);
if(cookie != 0) {
parser = assmgr.openXmlResourceParser(cookie, "AndroidManifest.xml");
assetError = false;
} else {
......
}
} catch (Exception e) {
......
}
......
String[] errorText = new String[1];
Package pkg = null;
Exception errorException = null;
try {
// XXXX todo: need to figure out correct configuration.
Resources res = new Resources(assmgr, metrics, null);
pkg = parsePackage(res, parser, flags, errorText);
} catch (Exception e) {
......
}
......
parser.close();
assmgr.close();
// Set code and resource paths
pkg.mPath = destCodePath;
pkg.mScanPath = mArchiveSourcePath;
//pkg.applicationInfo.sourceDir = destCodePath;
//pkg.applicationInfo.publicSourceDir = destRes;
pkg.mSignatures = null;
return pkg;
}
......
} 每一個Apk文件都是一個歸檔文件，它里面包含了Android應用程序的配置文件AndroidManifest.xml，這里主要就是要對這個配置文件就行解析了，從Apk歸檔文件中得到這個配置文件后，就調用另一外版本的parsePackage函數對這個應用程序進行解析了：
public class PackageParser {
......
private Package parsePackage(
Resources res, XmlResourceParser parser, int flags, String[] outError)
throws XmlPullParserException, IOException {
......
String pkgName = parsePackageName(parser, attrs, flags, outError);
......
final Package pkg = new Package(pkgName);
......
int type;
......
TypedArray sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifest);
......
while ((type=parser.next()) != parser.END_DOCUMENT
&& (type != parser.END_TAG || parser.getDepth() > outerDepth)) {
if (type == parser.END_TAG || type == parser.TEXT) {
continue;
}
String tagName = parser.getName();
if (tagName.equals("application")) {
......
if (!parseApplication(pkg, res, parser, attrs, flags, outError)) {
return null;
}
} else if (tagName.equals("permission-group")) {
......
} else if (tagName.equals("permission")) {
......
} else if (tagName.equals("permission-tree")) {
......
} else if (tagName.equals("uses-permission")) {
......
} else if (tagName.equals("uses-configuration")) {
......
} else if (tagName.equals("uses-feature")) {
......
} else if (tagName.equals("uses-sdk")) {
......
} else if (tagName.equals("supports-screens")) {
......
} else if (tagName.equals("protected-broadcast")) {
......
} else if (tagName.equals("instrumentation")) {
......
} else if (tagName.equals("original-package")) {
......
} else if (tagName.equals("adopt-permissions")) {
......
} else if (tagName.equals("uses-gl-texture")) {
......
} else if (tagName.equals("compatible-screens")) {
......
} else if (tagName.equals("eat-comment")) {
......
} else if (RIGID_PARSER) {
......
} else {
......
}
}
......
return pkg;
}
......
} 這里就是對AndroidManifest.xml文件中的各個標簽進行解析了，各個標簽的含義可以參考官方文檔
http://developer.android.com/guide/topics/manifest/manifest-intro.html，這里我們只簡單看一下application標簽的解析，這是通過調用parseApplication函數來進行的。
Step 11. PackageParser.parseApplication
這個函數定義在frameworks/base/core/java/android/content/pm/PackageParser.java文件中：
public class PackageParser {
......
private boolean parseApplication(Package owner, Resources res,
XmlPullParser parser, AttributeSet attrs, int flags, String[] outError)
throws XmlPullParserException, IOException {
final ApplicationInfo ai = owner.applicationInfo;
final String pkgName = owner.applicationInfo.packageName;
TypedArray sa = res.obtainAttributes(attrs,
com.android.internal.R.styleable.AndroidManifestApplication);
......
int type;
while ((type=parser.next()) != parser.END_DOCUMENT
&& (type != parser.END_TAG || parser.getDepth() > innerDepth)) {
if (type == parser.END_TAG || type == parser.TEXT) {
continue;
}
String tagName = parser.getName();
if (tagName.equals("activity")) {
Activity a = parseActivity(owner, res, parser, attrs, flags, outError, false);
......
owner.activities.add(a);
} else if (tagName.equals("receiver")) {
Activity a = parseActivity(owner, res, parser, attrs, flags, outError, true);
......
owner.receivers.add(a);
} else if (tagName.equals("service")) {
Service s = parseService(owner, res, parser, attrs, flags, outError);
......
owner.services.add(s);
} else if (tagName.equals("provider")) {
Provider p = parseProvider(owner, res, parser, attrs, flags, outError);
......
owner.providers.add(p);
} else if (tagName.equals("activity-alias")) {
Activity a = parseActivityAlias(owner, res, parser, attrs, flags, outError);
......
owner.activities.add(a);
} else if (parser.getName().equals("meta-data")) {
......
} else if (tagName.equals("uses-library")) {
......
} else if (tagName.equals("uses-package")) {
......
} else {
......
}
}
return true;
}
......
} 這里就是對AndroidManifest.xml文件中的application標簽進行解析了，我們常用到的標簽就有activity、service、receiver和provider，各個標簽的含義可以參考官方文檔
http://developer.android.com/guide/topics/manifest/manifest-intro.html。
這里解析完成后，一層層返回到Step 9中，調用另一個版本的scanPackageLI函數把來解析后得到的應用程序信息保存下來。
Step 12. PackageManagerService.scanPackageLI
這個函數定義在frameworks/base/services/java/com/android/server/PackageManagerService.java文件中：
class PackageManagerService extends IPackageManager.Stub {
......
// Keys are String (package name), values are Package. This also serves
// as the lock for the global state. Methods that must be called with
// this lock held have the prefix "LP".
final HashMap<String, PackageParser.Package> mPackages =
new HashMap<String, PackageParser.Package>();
......
// All available activities, for your resolving pleasure.
final ActivityIntentResolver mActivities =
new ActivityIntentResolver();
// All available receivers, for your resolving pleasure.
final ActivityIntentResolver mReceivers =
new ActivityIntentResolver();
// All available services, for your resolving pleasure.
final ServiceIntentResolver mServices = new ServiceIntentResolver();
// Keys are String (provider class name), values are Provider.
final HashMap<ComponentName, PackageParser.Provider> mProvidersByComponent =
new HashMap<ComponentName, PackageParser.Provider>();
......
private PackageParser.Package scanPackageLI(PackageParser.Package pkg,
int parseFlags, int scanMode, long currentTime) {
......
synchronized (mPackages) {
......
// Add the new setting to mPackages
mPackages.put(pkg.applicationInfo.packageName, pkg);
......
int N = pkg.providers.size();
int i;
for (i=0; i<N; i++) {
PackageParser.Provider p = pkg.providers.get(i);
p.info.processName = fixProcessName(pkg.applicationInfo.processName,
p.info.processName, pkg.applicationInfo.uid);
mProvidersByComponent.put(new ComponentName(p.info.packageName,
p.info.name), p);
......
}
N = pkg.services.size();
for (i=0; i<N; i++) {
PackageParser.Service s = pkg.services.get(i);
s.info.processName = fixProcessName(pkg.applicationInfo.processName,
s.info.processName, pkg.applicationInfo.uid);
mServices.addService(s);
......
}
N = pkg.receivers.size();
r = null;
for (i=0; i<N; i++) {
PackageParser.Activity a = pkg.receivers.get(i);
a.info.processName = fixProcessName(pkg.applicationInfo.processName,
a.info.processName, pkg.applicationInfo.uid);
mReceivers.addActivity(a, "receiver");
......
}
N = pkg.activities.size();
for (i=0; i<N; i++) {
PackageParser.Activity a = pkg.activities.get(i);
a.info.processName = fixProcessName(pkg.applicationInfo.processName,
a.info.processName, pkg.applicationInfo.uid);
mActivities.addActivity(a, "activity");
......
}
......
}
......
return pkg;
}
......
} 這個函數主要就是把前面解析應用程序得到的package、provider、service、receiver和activity等信息保存在PackageManagerService服務中了。
這樣，在Android系統啟動的時候安裝應用程序的過程就介紹完了，但是，這些應用程序只是相當于在PackageManagerService服務注冊好了，如果我們想要在Android桌面上看到這些應用程序，還需要有一個Home應用程序，負責從PackageManagerService服務中把這些安裝好的應用程序取出來，并以友好的方式在桌面上展現出來，例如以快捷圖標的形式。在Android系統中，負責把系統中已經安裝的應用程序在桌面中展現出來的Home應用程序就是Launcher了，在下一篇文章中，我們將介紹Launcher是如何啟動的以及它是如何從PackageManagerService服務中把系統中已經安裝好的應用程序展現出來的，敬請期待。
作者：Luoshengyang 發表于2011-9-14 0:59:22
原文鏈接
posted on 2012-04-17 21:32
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