閑來沒事看看源碼蓝晒，于是寫了這篇腮出，本文主要介紹Android以及Activity的主要?jiǎng)?chuàng)建流程，所有流程基于Android8.1的代碼芝薇，在部分流程尤其是activity與之前版本存在較大差異胚嘲，供大家參考。
一洛二、Android啟動(dòng)流程
我們直接進(jìn)到app_main.cpp進(jìn)行查看了
int main(int argc, char* const argv[]){
runtime.start("com.android.internal.os.ZygoteInit", args, zygote);
}
AndroidRuntime.cpp
void AndroidRuntime::start(const char* className,
const Vector<String8>& options, bool zygote){
if (startVm(&mJavaVM, &env, zygote) != 0) {
return;
}
onVmCreated(env);
}
int AndroidRuntime::startVm(JavaVM** pJavaVM, JNIEnv** pEnv, bool zygote){
/*
* Register android functions.
*/
if (startReg(env) < 0) {
ALOGE("Unable to register all android natives\n");
return;
}
}
/*static*/ int AndroidRuntime::startReg(JNIEnv* env){
/*
* Every "register" function calls one or more things that return
* a local reference (e.g. FindClass). Because we haven't really
* started the VM yet, they're all getting stored in the base frame
* and never released. Use Push/Pop to manage the storage.
*/
env->PushLocalFrame(200);
if (register_jni_procs(gRegJNI, NELEM(gRegJNI), env) < 0) {
env->PopLocalFrame(NULL);
return -1;
}
env->PopLocalFrame(NULL);
}
gRegJNI注冊(cè)了很多的函數(shù)：
static const RegJNIRec gRegJNI[] = {
REG_JNI(register_com_android_internal_os_ZygoteInit_nativeZygoteInit),
//...
}
register_com_android_internal_os_ZygoteInit_nativeZygoteInit定義為：
int register_com_android_internal_os_ZygoteInit_nativeZygoteInit(JNIEnv* env)
{
const JNINativeMethod methods[] = {
{ "nativeZygoteInit", "()V",
(void*) com_android_internal_os_ZygoteInit_nativeZygoteInit },
};
return jniRegisterNativeMethods(env, "com/android/internal/os/ZygoteInit",
methods, NELEM(methods));
}
終于看到ZygoteInit馋劈。進(jìn)入看看：ZygoteInit.java
public static void main(String argv[]) {
zygoteServer.registerServerSocket(socketName);
Runnable r = forkSystemServer(abiList, socketName, zygoteServer);
r.run();
// The select loop returns early in the child process after a fork and
// loops forever in the zygote.
caller = zygoteServer.runSelectLoop(abiList);
}
可知一共做了三件事：1）創(chuàng)建了一個(gè)socket接口，用來和ActivityManagerService通訊灭红。
2）啟動(dòng)SystemServer組件侣滩。3）創(chuàng)建一個(gè)loop用來接聽socket接口上ActivityManagerService的請(qǐng)求，來創(chuàng)建新的應(yīng)用進(jìn)程变擒。
接著我們主要看一下SystemServer的流程：SystemServer.java
/**
* The main entry point from zygote.
*/
public static void main(String[] args) {
new SystemServer().run();
}
private void run() {
// Ensure binder calls into the system always run at foreground priority.
BinderInternal.disableBackgroundScheduling(true);
// Increase the number of binder threads in system_server
BinderInternal.setMaxThreads(sMaxBinderThreads);//31
// Prepare the main looper thread (this thread).
android.os.Process.setThreadPriority(
android.os.Process.THREAD_PRIORITY_FOREGROUND);//-2
android.os.Process.setCanSelfBackground(false);
Looper.prepareMainLooper();
// Initialize native services.
System.loadLibrary("android_servers");
// Check whether we failed to shut down last time we tried.
// This call may not return.
performPendingShutdown();
// Initialize the system context.
createSystemContext();
// Create the system service manager.
mSystemServiceManager = new SystemServiceManager(mSystemContext);
mSystemServiceManager.setRuntimeRestarted(mRuntimeRestart);
LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
// Prepare the thread pool for init tasks that can be parallelized
SystemServerInitThreadPool.get();
// Start services.
startBootstrapServices();
/**
* Starts some essential services that are not tangled up in the bootstrap process.
*/
startCoreServices();
/**
* Starts a miscellaneous grab bag of stuff that has yet to be refactored
* and organized.
*/
startOtherServices();
SystemServerInitThreadPool.shutdown();
}
這里其實(shí)主要做了兩件事情：1）createSystemContext進(jìn)行了一些activity相關(guān)的配置君珠。2）創(chuàng)建了很多service。下面先看第一個(gè)：
private void createSystemContext() {
ActivityThread activityThread = ActivityThread.systemMain();
mSystemContext = activityThread.getSystemContext();
mSystemContext.setTheme(DEFAULT_SYSTEM_THEME);
}
public static ActivityThread systemMain() {
//...
ActivityThread thread = new ActivityThread();
thread.attach(true);
return thread;
}
private void attach(boolean system) {//true
mInstrumentation = new Instrumentation();//新建Instrumentation
ContextImpl context = ContextImpl.createAppContext(
this, getSystemContext().mPackageInfo);
mInitialApplication = context.mPackageInfo.makeApplication(true, null);//啟動(dòng)application
mInitialApplication.onCreate();
}
可見娇斑，在此創(chuàng)建了Instrumentation策添、ContextImpl等工作材部。
接著看一下上面的service創(chuàng)建。從上面可見唯竹，SystemServer創(chuàng)建了SystemServiceManager乐导，直接進(jìn)行了初始化了很多service：
startBootstrapServices();
startCoreServices();
startOtherServices();
startBootstrapServices就是啟動(dòng)了最著名的ActivityManagerService（AMS)，其中還有PowerManagerService浸颓、PackageManagerService：
private void startBootstrapServices() {
// Activity manager runs the show.
traceBeginAndSlog("StartActivityManager");
mActivityManagerService = mSystemServiceManager.startService(
ActivityManagerService.Lifecycle.class).getService();
mActivityManagerService.setSystemServiceManager(mSystemServiceManager);
mActivityManagerService.setInstaller(installer);
traceEnd();
mPowerManagerService = mSystemServiceManager.startService(PowerManagerService.class);
mPackageManagerService = PackageManagerService.main(mSystemContext, installer,
mFactoryTestMode != FactoryTest.FACTORY_TEST_OFF, mOnlyCore);
}
可能也都看到了他們都是通過mSystemServiceManager創(chuàng)建的物臂，為什么呢？其實(shí)是因?yàn)檫@些所有的service都是要注冊(cè)在SystemServiceManager之中進(jìn)行同意管理的产上。
public class SystemServiceManager {
private final ArrayList<SystemService> mServices = new ArrayList<SystemService>();
public void startService(@NonNull final SystemService service) {
// Register it.
mServices.add(service);
// Start it.
service.onStart();
//...
}
上面的SystemServer.run()還有幾個(gè)點(diǎn)需要關(guān)注一下:
// maximum number of binder threads used for system_server
// will be higher than the system default
private static final int sMaxBinderThreads = 31;
// Ensure binder calls into the system always run at foreground priority.
BinderInternal.disableBackgroundScheduling(true);
// Increase the number of binder threads in system_server
BinderInternal.setMaxThreads(sMaxBinderThreads);
binder進(jìn)程的請(qǐng)求數(shù)量是在這里設(shè)置的默認(rèn)為31棵磷，并且運(yùn)行在foreground priority，同樣SystemService進(jìn)程優(yōu)先級(jí)也是foreground priority且不可置為后臺(tái)：
android.os.Process.setThreadPriority(
android.os.Process.THREAD_PRIORITY_FOREGROUND);//-2
android.os.Process.setCanSelfBackground(false);
foreground priority在所有優(yōu)先級(jí)中的位置：
public static final int THREAD_PRIORITY_AUDIO = -16;
public static final int THREAD_PRIORITY_BACKGROUND = 10;
public static final int THREAD_PRIORITY_DEFAULT = 0;
public static final int THREAD_PRIORITY_DISPLAY = -4;
public static final int THREAD_PRIORITY_FOREGROUND = -2;
public static final int THREAD_PRIORITY_LESS_FAVORABLE = 1;
public static final int THREAD_PRIORITY_LOWEST = 19;
public static final int THREAD_PRIORITY_MORE_FAVORABLE = -1;
public static final int THREAD_PRIORITY_URGENT_AUDIO = -19;
public static final int THREAD_PRIORITY_URGENT_DISPLAY = -8;
平時(shí)我們使用的Activity在THREAD_PRIORITY_DEFAULT晋涣，Async在THREAD_PRIORITY_BACKGROUND仪媒。
OK，現(xiàn)在為止啟動(dòng)流程基本介紹完了谢鹊。
二算吩、Activity啟動(dòng)流程
讓我們看一下activity啟動(dòng)流程，假設(shè)由桌面點(diǎn)擊應(yīng)用圖標(biāo)來啟動(dòng)：
Launcher.java
public void onClick(View v)
boolean startActivitySafely(View v, Intent intent, Object tag)
boolean startActivity(View v, Intent intent, Object tag)
startActivity(intent);
Activity.java
public void startActivity(Intent intent)
public void startActivity(Intent intent, @Nullable Bundle options)
public void startActivityForResult(@RequiresPermission Intent intent, int requestCode,
@Nullable Bundle options)
Instrumentation.java
public ActivityResult execStartActivity(
Context who, IBinder contextThread, IBinder token, Activity target,
Intent intent, int requestCode, Bundle options){
ActivityManager.getService()
.startActivity(whoThread, who.getBasePackageName(), intent,
intent.resolveTypeIfNeeded(who.getContentResolver()),
token, target != null ? target.mEmbeddedID : null,
requestCode, 0, null, options);
}
這里最終調(diào)用了ActivityManager的getService方法佃扼，從返回值IActivityManager就可以看出來應(yīng)該是進(jìn)行了跨進(jìn)程通訊偎巢。
//ActivityManager.java
public static IActivityManager getService() {
return IActivityManagerSingleton.get();
}
private static final Singleton<IActivityManager> IActivityManagerSingleton =
new Singleton<IActivityManager>() {
@Override
protected IActivityManager create() {
final IBinder b = ServiceManager.getService(Context.ACTIVITY_SERVICE);
final IActivityManager am = IActivityManager.Stub.asInterface(b);
return am;
}
};
很明顯這里是AIDL客戶端調(diào)用，他的接口定義為：
//IActivityManager.aidl
int startActivity(in IApplicationThread caller, in String callingPackage, in Intent intent,
in String resolvedType, in IBinder resultTo, in String resultWho, int requestCode,
int flags, in ProfilerInfo profilerInfo, in Bundle options);
想要繼續(xù)根據(jù)我們的找到服務(wù)端的代碼松嘶，這個(gè)服務(wù)端的代碼其實(shí)并不是很好找的艘狭，這里我使用了全局搜索，最終中油一個(gè)調(diào)用點(diǎn):ActivityManagerService.java（如果大家有好的查找方法翠订，懇請(qǐng)告知巢音，謝謝），找到了服務(wù)端代碼下面的跟進(jìn)就很方便了：
public class ActivityManagerService extends IActivityManager.Stub
public final int startActivity(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle bOptions)
frameworks/base/services/core/java/com/android/server/am/ActivityStarter.java
public final int startActivityAsUser(IApplicationThread caller, String callingPackage,
Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId)
final int startActivityMayWait(IApplicationThread caller, int callingUid,
String callingPackage, Intent intent, String resolvedType,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode, int startFlags,
ProfilerInfo profilerInfo, WaitResult outResult,
Configuration globalConfig, Bundle bOptions, boolean ignoreTargetSecurity, int userId,
TaskRecord inTask, String reason)
int startActivityLocked(IApplicationThread caller, Intent intent, Intent ephemeralIntent,
String resolvedType, ActivityInfo aInfo, ResolveInfo rInfo,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode, int callingPid, int callingUid,
String callingPackage, int realCallingPid, int realCallingUid, int startFlags,
ActivityOptions options, boolean ignoreTargetSecurity, boolean componentSpecified,
ActivityRecord[] outActivity, TaskRecord inTask, String reason)
private int startActivity(IApplicationThread caller, Intent intent, Intent ephemeralIntent,
String resolvedType, ActivityInfo aInfo, ResolveInfo rInfo,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode, int callingPid, int callingUid,
String callingPackage, int realCallingPid, int realCallingUid, int startFlags,
ActivityOptions options, boolean ignoreTargetSecurity, boolean componentSpecified,
ActivityRecord[] outActivity, TaskRecord inTask)
private int startActivity(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
ActivityRecord[] outActivity)
private int startActivityUnchecked(final ActivityRecord r, ActivityRecord sourceRecord,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
int startFlags, boolean doResume, ActivityOptions options, TaskRecord inTask,
ActivityRecord[] outActivity)
frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.java
boolean resumeFocusedStackTopActivityLocked(
ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
frameworks/base/services/core/java/com/android/server/am/ActivityStack.java
boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options)
private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options)
final boolean startPausingLocked(boolean userLeaving, boolean uiSleeping,
ActivityRecord resuming, boolean pauseImmediately) {
prev.app.thread.schedulePauseActivity(prev.appToken, prev.finishing,
userLeaving, prev.configChangeFlags, pauseImmediately);
}
跨進(jìn)程通信
frameworks/base/core/java/android/app/ActivityThread.java
public final void schedulePauseActivity(IBinder token, boolean finished,
boolean userLeaving, int configChanges, boolean dontReport)
public void handleMessage(Message msg) {
case PAUSE_ACTIVITY: {
handlePauseActivity((IBinder) args.arg1, false,
(args.argi1 & USER_LEAVING) != 0, args.argi2,
(args.argi1 & DONT_REPORT) != 0, args.argi3);
} break;
}
private void handlePauseActivity(IBinder token, boolean finished,
boolean userLeaving, int configChanges, boolean dontReport, int seq)
跨進(jìn)程通信
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public final void activityPaused(IBinder token)
frameworks/base/services/core/java/com/android/server/am/ActivityStack.java
final void activityPausedLocked(IBinder token, boolean timeout)
final void startActivityLocked(ActivityRecord r, ActivityRecord focusedTopActivity,
boolean newTask, boolean keepCurTransition, ActivityOptions options)
frameworks/base/services/core/java/com/android/server/am/ActivityStack.java
private void completePauseLocked(boolean resumeNext, ActivityRecord resuming)
frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.java
boolean resumeFocusedStackTopActivityLocked(
ActivityStack targetStack, ActivityRecord target, ActivityOptions targetOptions) {
frameworks/base/services/core/java/com/android/server/am/ActivityStack.java
boolean resumeTopActivityUncheckedLocked(ActivityRecord prev, ActivityOptions options)
private boolean resumeTopActivityInnerLocked(ActivityRecord prev, ActivityOptions options)
frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.java
void startSpecificActivityLocked(ActivityRecord r,
boolean andResume, boolean checkConfig)
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
final ProcessRecord startProcessLocked(String processName,
ApplicationInfo info, boolean knownToBeDead, int intentFlags,
String hostingType, ComponentName hostingName, boolean allowWhileBooting,
boolean isolated, boolean keepIfLarge)
final ProcessRecord startProcessLocked(String processName, ApplicationInfo info,
boolean knownToBeDead, int intentFlags, String hostingType, ComponentName hostingName,
boolean allowWhileBooting, boolean isolated, int isolatedUid, boolean keepIfLarge,
String abiOverride, String entryPoint, String[] entryPointArgs, Runnable crashHandler)
private final void startProcessLocked(ProcessRecord app, String hostingType,
String hostingNameStr, String abiOverride, String entryPoint, String[] entryPointArgs) {
startResult = Process.start(entryPoint,
app.processName, uid, uid, gids, debugFlags, mountExternal,
app.info.targetSdkVersion, seInfo, requiredAbi, instructionSet,
app.info.dataDir, invokeWith, entryPointArgs);
}
frameworks/base/core/java/android/os/Process.java
zygoteProcess.start(processClass, niceName, uid, gid, gids,
debugFlags, mountExternal, targetSdkVersion, seInfo,
abi, instructionSet, appDataDir, invokeWith, zygoteArgs);
產(chǎn)生了新的ActivityThread進(jìn)程尽超，然后執(zhí)行進(jìn)程的main方法官撼。
frameworks/base/core/java/android/app/ActivityThread.java
public static void main(String[] args) {
Looper.prepareMainLooper();
ActivityThread thread = new ActivityThread();
thread.attach(false);
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
if (false) {
Looper.myLooper().setMessageLogging(new
LogPrinter(Log.DEBUG, "ActivityThread"));
}
Looper.loop();
}
private void attach(boolean system) {//false
final IActivityManager mgr = ActivityManager.getService();
mgr.attachApplication(mAppThread);
}
跨進(jìn)程
frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public final void attachApplication(IApplicationThread thread)
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid)
frameworks/base/services/core/java/com/android/server/am/ActivityStackSupervisor.java
boolean attachApplicationLocked(ProcessRecord app) throws RemoteException
final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,
boolean andResume, boolean checkConfig) throws RemoteException {
app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
System.identityHashCode(r), r.info,
mergedConfiguration.getGlobalConfiguration(),
mergedConfiguration.getOverrideConfiguration(), r.compat,
r.launchedFromPackage, task.voiceInteractor, app.repProcState, r.icicle,
r.persistentState, results, newIntents, !andResume,
mService.isNextTransitionForward(), profilerInfo);
}
frameworks/base/core/java/android/app/ActivityThread.java$ApplicationThread
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Configuration curConfig, Configuration overrideConfig,
CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor,
int procState, Bundle state, PersistableBundle persistentState,
List<ResultInfo> pendingResults, List<ReferrerIntent> pendingNewIntents,
boolean notResumed, boolean isForward, ProfilerInfo profilerInfo)
private void sendMessage(int what, Object obj)
public void handleMessage(Message msg) {
case LAUNCH_ACTIVITY: {
handleLaunchActivity(r, null, "LAUNCH_ACTIVITY");
} break;
}
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason)
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent){
ContextImpl appContext = createBaseContextForActivity(r);
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent)
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstances, config,
r.referrer, r.voiceInteractor, window, r.configCallback);
mInstrumentation.callActivityOnCreate(activity, r.state);
}
public void callActivityOnCreate(Activity activity, Bundle icicle) {
prePerformCreate(activity);
activity.performCreate(icicle);
postPerformCreate(activity);
}
frameworks/base/core/java/android/app/Activity.java
final void performCreate(Bundle icicle, PersistableBundle persistentState)
protected void onCreate(@Nullable Bundle savedInstanceState)
最后，時(shí)序圖先補(bǔ)一張以前版本的似谁，最近補(bǔ)上傲绣。
activity啟動(dòng)流程圖old.jpg
