继 Android应用程序（activity）启动过程（一），主要讲新进程和activity如何启动
yipianfengye_activity启动流程
- 从 第14步骤 调用 ActivityStack resumeTopActivityInnerLocked方法中最后面有一个方法startSpecificActivityLocked()。
if (!next.hasBeenLaunched) {
next.hasBeenLaunched = true;
} else {
if (SHOW_APP_STARTING_PREVIEW) {
next.showStartingWindow(null /* prev */, false /* newTask */,
false /* taskSwich */);
}
if (DEBUG_SWITCH) Slog.v(TAG_SWITCH, "Restarting: " + next);
}
if (DEBUG_STATES) Slog.d(TAG_STATES, "resumeTopActivityLocked: Restarting " + next);
// 开始启动新 activity
mStackSupervisor.startSpecificActivityLocked(next, true, true);
- 在startSpecificActivityLocked()判断当前Activity所需要的应用进程是否已经启动，若启动的话，则直接调用realStartAtivityLocked方法，否则调用startProcessLocked方法，用于启动应用进程
void startSpecificActivityLocked(ActivityRecord r,
boolean andResume, boolean checkConfig) {
// Is this activity's application already running?
ProcessRecord app = mService.getProcessRecordLocked(r.processName,
r.info.applicationInfo.uid, true);
r.getStack().setLaunchTime(r);
if (app != null && app.thread != null) {
try {
if ((r.info.flags&ActivityInfo.FLAG_MULTIPROCESS) == 0
|| !"android".equals(r.info.packageName)) {
app.addPackage(r.info.packageName, r.info.applicationInfo.versionCode,
mService.mProcessStats);
}
// 进程已经启动
realStartActivityLocked(r, app, andResume, checkConfig);
return;
} catch (RemoteException e) {
Slog.w(TAG, "Exception when starting activity "
+ r.intent.getComponent().flattenToShortString(), e);
}
// If a dead object exception was thrown -- fall through to
// restart the application.
}
mService.startProcessLocked(r.processName, r.info.applicationInfo, true, 0,
"activity", r.intent.getComponent(), false, false, true);
}
- 先查看进程未启动的情况 进入ActivityManagerService.startProcessLocked()
经过两次的方法重写，可以看到下面一段代码，在start()时传入了android.app.ActivityThread字符串，正式启动一个新进程
if (entryPoint == null) entryPoint = "android.app.ActivityThread";
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "Start proc: " +
app.processName);
checkTime(startTime, "startProcess: asking zygote to start proc");
Process.ProcessStartResult startResult = Process.start(entryPoint,
app.processName, uid, uid, gids, debugFlags, mountExternal,
app.info.targetSdkVersion, app.info.seinfo, requiredAbi, instructionSet,
app.info.dataDir, entryPointArgs);
- 在Process.start()中 代码很简单，直接进入到startViaZygote() 翻译：开始孵化？
try {
return startViaZygote(processClass, niceName, uid, gid, gids,
debugFlags, mountExternal, targetSdkVersion, seInfo,
abi, instructionSet, appDataDir, zygoteArgs);
} catch (ZygoteStartFailedEx ex) {
Log.e(LOG_TAG,
"Starting VM process through Zygote failed");
throw new RuntimeException(
"Starting VM process through Zygote failed", ex);
}
- 在startViaZygote()方法中又直接调用了zygoteSendArgsAndGetResult();
private static ProcessStartResult zygoteSendArgsAndGetResult(
ZygoteState zygoteState, ArrayList<String> args)
throws ZygoteStartFailedEx {
try {
// Throw early if any of the arguments are malformed. This means we can
// avoid writing a partial response to the zygote.
int sz = args.size();
for (int i = 0; i < sz; i++) {
if (args.get(i).indexOf('\n') >= 0) {
throw new ZygoteStartFailedEx("embedded newlines not allowed");
}
}
final BufferedWriter writer = zygoteState.writer;
final DataInputStream inputStream = zygoteState.inputStream;
writer.write(Integer.toString(args.size()));
writer.newLine();
for (int i = 0; i < sz; i++) {
String arg = args.get(i);
writer.write(arg);
writer.newLine();
}
writer.flush();
// Should there be a timeout on this?
ProcessStartResult result = new ProcessStartResult();
// Always read the entire result from the input stream to avoid leaving
// bytes in the stream for future process starts to accidentally stumble
// upon.
result.pid = inputStream.readInt();
result.usingWrapper = inputStream.readBoolean();
if (result.pid < 0) {
throw new ZygoteStartFailedEx("fork() failed");
}
return result;
} catch (IOException ex) {
zygoteState.close();
throw new ZygoteStartFailedEx(ex);
}
}
可以发现其最终调用了Zygote并通过socket通信的方式让Zygote进程fork除了一个新的进程，并根据我们刚刚传递的"android.app.ActivityThread"字符串，反射出该对象并执行ActivityThread的main方法。这样我们所要启动的应用进程这时候其实已经启动了，但是还没有执行相应的初始化操作。
43. 通过 openZygoteSocketIfNeeded(）---->ZygoteState.connect()---->zygoteSocket.connect()---->impl.connect(),调用Native方法connectLocal()。具体进程怎么启动的这又是一个话题。。。
44. 当进程启动完成后就进入ActivityThread类的main方法
public static void main(String[] args) {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "ActivityThreadMain");
... ...
EventLogger.setReporter(new EventLoggingReporter());
... ...
Process.setArgV0("<pre-initialized>");
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();
throw new RuntimeException("Main thread loop unexpectedly exited");
}
- 在main方法中调用了Looper.prepareMainLooper(); Looper.loop();方法，这就是为什么在activity（主线程）直接new handler，使用handler不报错的原因，在子线程要先调用prepare方法。下面是主要方法 thread.attach(false);
final IActivityManager mgr = ActivityManagerNative.getDefault();
try {
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
- 通过ActivityManagerNative中ActivityManagerProxy的attachApplication方法发送到服务端，ActivityManagerNative的实现类ActivityManagerService中attachApplication()
@Override
public final void attachApplication(IApplicationThread thread) {
synchronized (this) {
int callingPid = Binder.getCallingPid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid);
Binder.restoreCallingIdentity(origId);
}
}
- 代码很简洁，直接进入attachApplicationLocked
// See if the top visible activity is waiting to run in this process...
if (normalMode) {
try {
if (mStackSupervisor.attachApplicationLocked(app)) {
didSomething = true;
}
} catch (Exception e) {
Slog.wtf(TAG, "Exception thrown launching activities in " + app, e);
badApp = true;
}
}
- 摸索到了这一段代码 mStackSupervisor.attachApplicationLocked(app)
boolean attachApplicationLocked(ProcessRecord app) throws RemoteException {
final String processName = app.processName;
boolean didSomething = false;
for (int displayNdx = mActivityDisplays.size() - 1; displayNdx >= 0; --displayNdx) {
ArrayList<ActivityStack> stacks = mActivityDisplays.valueAt(displayNdx).mStacks;
for (int stackNdx = stacks.size() - 1; stackNdx >= 0; --stackNdx) {
final ActivityStack stack = stacks.get(stackNdx);
if (!isFocusedStack(stack)) {
continue;
}
ActivityRecord hr = stack.topRunningActivityLocked();
if (hr != null) {
if (hr.app == null && app.uid == hr.info.applicationInfo.uid
&& processName.equals(hr.processName)) {
try {
if (realStartActivityLocked(hr, app, true, true)) {
didSomething = true;
}
} catch (RemoteException e) {
Slog.w(TAG, "Exception in new application when starting activity "
+ hr.intent.getComponent().flattenToShortString(), e);
throw e;
}
}
}
}
}
if (!didSomething) {
ensureActivitiesVisibleLocked(null, 0, !PRESERVE_WINDOWS);
}
return didSomething;
}
- 我又重新看到了realStartActivityLocked()，又找到了组织，重新回到 step.39。这时候就是开始启动activity了
app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration),
new Configuration(task.mOverrideConfig), r.compat, r.launchedFromPackage,
task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results,
newIntents, !andResume, mService.isNextTransitionForward(), profilerInfo);
- 通过IApplicationThread调用了scheduleLaunchActivity，最终实现是在ActivityThread内部类ApplicationThread实现的，然后通过Handler调用handleLaunchActivity()
case LAUNCH_ACTIVITY: {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
final ActivityClientRecord r = (ActivityClientRecord) msg.obj;
r.packageInfo = getPackageInfoNoCheck(
r.activityInfo.applicationInfo, r.compatInfo);
handleLaunchActivity(r, null, "LAUNCH_ACTIVITY");
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
} break;
- ActivityThread类 handleLaunchActivity 中有performLaunchActivity，handleResumeActivity，performPauseActivityIfNeeded
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) {
... ...
Activity a = performLaunchActivity(r, customIntent);
if (a != null) {
r.createdConfig = new Configuration(mConfiguration);
reportSizeConfigurations(r);
Bundle oldState = r.state;
... ...
handleResumeActivity(r.token, false, r.isForward,
!r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason);
if (!r.activity.mFinished && r.startsNotResumed) {
... ...
performPauseActivityIfNeeded(r, reason);
.. ..
if (r.isPreHoneycomb()) {
r.state = oldState;
}
}
} else {
try {
ActivityManagerNative.getDefault()
.finishActivity(r.token, Activity.RESULT_CANCELED, null,
Activity.DONT_FINISH_TASK_WITH_ACTIVITY);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
}
- performLaunchActivity中主要代码，newActivity(),通过类加载机制创建activity
try {
java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
StrictMode.incrementExpectedActivityCount(activity.getClass());
r.intent.setExtrasClassLoader(cl);
r.intent.prepareToEnterProcess();
if (r.state != null) {
r.state.setClassLoader(cl);
}
}
// 创建Activity通过类加载机制
public Activity newActivity(ClassLoader cl, String className,
Intent intent)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
return (Activity)cl.loadClass(className).newInstance();
}
- 还是当前方法，开始activity onCreate方法
activity.mCalled = false;
if (r.isPersistable()) {
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
} else {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
- 直接进入Instrumentation，
public void callActivityOnCreate(Activity activity, Bundle icicle) {
prePerformCreate(activity);
activity.performCreate(icicle);
postPerformCreate(activity);
}
// Activity
final void performCreate(Bundle icicle) {
restoreHasCurrentPermissionRequest(icicle);
onCreate(icicle);
mActivityTransitionState.readState(icicle);
performCreateCommon();
}
- 紧接着下面四五行代码，进入onstart()
if (!r.activity.mFinished) {
activity.performStart();
r.stopped = false;
}
- 恢复activity 被回收时保存的数据
if (!r.activity.mFinished) {
if (r.isPersistable()) {
if (r.state != null || r.persistentState != null) {
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state,
r.persistentState);
}
} else if (r.state != null) {
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
}
}
if (!r.activity.mFinished) {
activity.mCalled = false;
if (r.isPersistable()) {
// 活动启动完成时调用(在{@link #onStart}和{@link #onRestoreInstanceState}调用之后)。
应用程序通常不会实现这种方法;它用于系统类在应用程序代码运行之后进行最终初始化。，
mInstrumentation.callActivityOnPostCreate(activity, r.state,
r.persistentState);
} else {
mInstrumentation.callActivityOnPostCreate(activity, r.state);
}
if (!activity.mCalled) {
throw new SuperNotCalledException(
"Activity " + r.intent.getComponent().toShortString() +
" did not call through to super.onPostCreate()");
}
}
- 返回step 52 进入 handleResumeActivity，流程基本一样我就不往下分析了，现在及完成了activity onDestory到onCreate所有生命周期，祝大家收货满满！