Step 2. ActivityStack.activityIdleInternal
这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityStack.java文件中：
- public class ActivityStack {
- ......
- final void activityIdleInternal(IBinder token, boolean fromTimeout,
- Configuration config) {
- ......
- ArrayList<ActivityRecord> stops = null;
- ......
- int NS = 0;
- ......
- synchronized (mService) {
- ......
- // Atomically retrieve all of the other things to do.
- stops = processStoppingActivitiesLocked(true);
- NS = stops != null ? stops.size() : 0;
- ......
- }
- int i;
- ......
- // Stop any activities that are scheduled to do so but have been
- // waiting for the next one to start.
- for (i=0; i<NS; i++) {
- ActivityRecord r = (ActivityRecord)stops.get(i);
- synchronized (mService) {
- if (r.finishing) {
- finishCurrentActivityLocked(r, FINISH_IMMEDIATELY);
- } else {
- ......
- }
- }
- }
- ......
- }
- ......
- }
这个函数首先会调用processStoppingActivitiesLocked函数把所有处于Stopped状态的Activity取回来，然后逐个分析它们，如果它们的ActivityRecord中的finishing成员变量为true，就说明这个Activity需要销毁了，于是，就调用finishCurrentActivityLocked函数来销毁它们。
Step 3. ActivityStack.finishCurrentActivityLocked
这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityStack.java文件中：
- public class ActivityStack {
- ......
- private final ActivityRecord finishCurrentActivityLocked(ActivityRecord r,
- int mode) {
- ......
- return finishCurrentActivityLocked(r, index, mode);
- }
- private final ActivityRecord finishCurrentActivityLocked(ActivityRecord r,
- int index, int mode) {
- ......
- // make sure the record is cleaned out of other places.
- mStoppingActivities.remove(r);
- mWaitingVisibleActivities.remove(r);
- ......
- final ActivityState prevState = r.state;
- r.state = ActivityState.FINISHING;
- if (mode == FINISH_IMMEDIATELY
- || prevState == ActivityState.STOPPED
- || prevState == ActivityState.INITIALIZING) {
- // If this activity is already stopped, we can just finish
- // it right now.
- return destroyActivityLocked(r, true) ? null : r;
- } else {
- ......
- }
- return r;
- }
- ......
- }
从上面的Step 2中传进来的参数mode为FINISH_IMMEDIATELY，并且这个即将要被销毁的Activity的状态为Stopped，因此，接下来就会调用destroyActivityLocked函数来销毁它。
Step 4. ActivityStack.destroyActivityLocked
这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityStack.java文件中：
- public class ActivityStack {
- ......
- final boolean destroyActivityLocked(ActivityRecord r,
- boolean removeFromApp) {
- ......
- boolean removedFromHistory = false;
- ......
- final boolean hadApp = r.app != null;
- if (hadApp) {
- ......
- try {
- ......
- r.app.thread.scheduleDestroyActivity(r, r.finishing,
- r.configChangeFlags);
- } catch (Exception e) {
- ......
- }
- ......
- } else {
- ......
- }
- ......
- return removedFromHistory;
- }
- ......
- }
在前面一篇文章Android应用程序启动过程源代码分析中，我们说到，每一个应用程序进程在ActivityManagerService中，都ProcessRecord记录与之对应，而每一个Activity，都是运行在一个进程上下文中，因此，在ActivityManagerService中，每一个ActivityRecord的app成员变量都应该指向一个ProcessRecord记录，于是，这里得到的hadApp为true。在ProcessRecord类中，有一个成员变量thread，它的类型为IApplicationThread。在文章Android应用程序启动过程源代码分析中，我们也曾经说过，每一个应用程序在启动的时候，它都会在内部创建一个ActivityThread对象，而在这个ActivityThread对象中，有一个成员变量mAppThread，它的类型为ApplicationThread，这是一个Binder对象，专门用来负责在应用程序和ActivityManagerService之间执行进程间通信工作的。应用程序在启动的时候，就会将这个Binder对象传递给ActivityManagerService，而ActivityManagerService就会把它保存在相应的ProcessRecord记录的thread成员变量中。因此，ProcessRecord记录的thread成员变量其实就是ApplicationThread对象的远程接口，于是，执行下面这个语句的时候：
- r.app.thread.scheduleDestroyActivity(r, r.finishing,
- r.configChangeFlags);
就会进入到ApplicationThread类中的scheduleDestroyActivity函数来。
Step 5. ApplicationThread.scheduleDestroyActivity
这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中：
- public final class ActivityThread {
- ......
- private final class ApplicationThread extends ApplicationThreadNative {
- ......
- public final void scheduleDestroyActivity(IBinder token, boolean finishing,
- int configChanges) {
- queueOrSendMessage(H.DESTROY_ACTIVITY, token, finishing ? 1 : 0,
- configChanges);
- }
- ......
- }
- ......
- }
这个函数调用外部类ActivityThread的queueOrSendMessage函数来往应用程序的消息队列中发送一个H.DESTROY_ACTIVITY消息，这个消息最终由ActivityThread类的handleDestroyActivity函数来处理。
