Android AMS 整体架构

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ActivityManagerService中常见的类及其作用，包括ActivityRecord，ProcessRecord，TaskRecord，ActivityStack，ActivityStackSupervisor。

ActivityRecord

Activity History Stack中的一个节点，代表了一个Activity实例在System_Server进程端的驻留对象。startActivity时，在ASS#startActivityLocked方法中通过new ActivityRecord()创建实例对象。

ProcessRecord

应用程序进程对象，表示一个应用程序，对应用程序的所有管理操作都依赖于它，通过ActivityManagerService#startProcessLocked()创建出来，Process.start()实际上是调用ZygoteServer来fork出一个新进程。

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// all activities running in the process(所有运行的Activity)
final ArrayList<ActivityRecord> activities = new ArrayList<>();
// all ServiceRecord running in this process
final ArraySet<ServiceRecord> services = new ArraySet<>();
// services that are currently executing code (need to remain foreground).
final ArraySet<ServiceRecord> executingServices = new ArraySet<>();
// All ConnectionRecord this process holds
final ArraySet<ConnectionRecord> connections = new ArraySet<>();
// all IIntentReceivers that are registered from this process.
final ArraySet<ReceiverList> receivers = new ArraySet<>();
// class (String) -> ContentProviderRecord
final ArrayMap<String, ContentProviderRecord> pubProviders = new ArrayMap<>();
// All ContentProviderRecord process is using
final ArrayList<ContentProviderConnection> conProviders = new ArrayList<>();

管理ActivityRecord

  • add: ASS#realStartActivityLocked()方法中，通过app.activities.add(r);将新的ActivityRecord添加到运行的activities列表中。
  • remove: ASK#destroyActivityLocked()方法中，通过r.app.activities.remove(r);将ActivityRecord从activities列表中移除。

TaskRecord

通常一个应用程序会包含至少一个TaskRecord对象，用于管理ActivityRecord，如果有Activity在定义时指定了android:taskAffinity，则在启动该Activity时，会创建一个新的TaskRecord。每次退出LaunchActivity之后，再次进入，会重新创建。

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{
    /** List of all activities in the task arranged in history order */
    final ArrayList<ActivityRecord> mActivities;
    /** Current stack */
    ActivityStack stack;
}

TaskRecord创建过程

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final int startActivityUncheckedLocked(final ActivityRecord r, ActivityRecord sourceRecord, ...) { // ASS
	// LaunchActivity: sourceRecord为空。
    if (reuseTask == null) {
        r.setTask(targetStack.createTaskRecord(getNextTaskId(),
                newTaskInfo != null ? newTaskInfo : r.info,
                newTaskIntent != null ? newTaskIntent : intent,
                voiceSession, voiceInteractor, !launchTaskBehind /* toTop */),
                taskToAffiliate);
    }
    // ...
	// SubActivity: sourceRecord为上一级页面。
    if (sourceRecord != null) {
        final TaskRecord sourceTask = sourceRecord.task;
        if (isLockTaskModeViolation(sourceTask)) {
            Slog.e(TAG, "Attempted Lock Task Mode violation r=" + r);
            return ActivityManager.START_RETURN_LOCK_TASK_MODE_VIOLATION;
        }
        targetStack = sourceTask.stack;
        targetStack.moveToFront("sourceStackToFront");  
    }
    // ...
}

从Launcher中点击图标启动一个Activity，在ASS#startActivityUncheckedLocked中通过createTaskRecord()中调用new TaskRecord()创建TaskRecord实例。其它二级页面Activity和LaunchActivity共用同一个TaskRecord。

管理ActivityRecord

  • add: ASK#startActivityLocked()->TaskRecord#addActivityToTop(r)->TaskRecord#addActivityAtIndex()将ActivityRecord实例添加到mActivities中。
  • remove: ASK#activityDestoryedLocked()->ASK#removeActivityFromHistoryLocked()->TaskRecord#removeActivity()从mActivities中移除ActivityRecord。

ActivityStack

State and management of a single stack of activities，Activity栈列表，一个应用程序对应一个该对象实例，每次退出LaunchActivity之后，再次进入，会重新创建。

ActivityStack创建过程:startActivityUncheckedLocked()->computeStackFocus()->createStackOnDisplay()->new ActivityStack()。

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{
    /**
     * The back history of all previous (and possibly still
     * running) activities.  It contains #TaskRecord objects.
     */
    private ArrayList<TaskRecord> mTaskHistory = new ArrayList<>();
}

管理TaskRecord

  • add: ASS#startActivityUncheckedLocked()->ASK#createTaskRecord()->ASK#addTask()->ASK#insertTaskAtTop(task)添加TaskRecord。

ASS/AMS: 整个Android系统中只有一个实例对象。