Activity启动源码分析-基于Android10(二)

总流程图

• Instrumentation
  负责调用Activity和Application生命周期。
• ActivityTaskManagerService
  负责Activity管理和调度等工作。android10中新增的
• ActivityManagerService
  负责管理四大组件和进程，包括生命周期和状态切换。
• ActivityTaskManagerInternal
  ActivityTaskManagerService对外提供的一个抽象类，真正的实现在ActivityTaskManagerService#LocalService
• ActivityThread
  管理应用程序进程中主线程的执行
• ActivityStackSupervisor
  负责所有Activity栈的管理
• TransactionExecutor
  主要作用是执行ClientTransaction
• ClientLifecycleManager
  生命周期的管理调用

客户端和服务端IPC通信

1.基于Android10的IPC

上篇文章Activity启动流程-基于Android10(一)已经讲到了 Instrumentation的execStartActivity方法。其实Android10版本和之前版本的代码是有区别。

execStartActivity：

frameworks\base\core\java\android\app\Instrumentation.java

	@UnsupportedAppUsage
    public ActivityResult execStartActivity(
            Context who, IBinder contextThread, IBinder token, String resultWho,
            Intent intent, int requestCode, Bundle options, UserHandle user) {
   //...省略部分代码
   try {
            intent.migrateExtraStreamToClipData();
            intent.prepareToLeaveProcess(who);
            // 重要代码
            int result = ActivityTaskManager.getService()
                .startActivityAsUser(whoThread, who.getBasePackageName(), intent,
                        intent.resolveTypeIfNeeded(who.getContentResolver()),
                        token, resultWho,
                        requestCode, 0, null, options, user.getIdentifier());
            checkStartActivityResult(result, intent);
        } catch (RemoteException e) {
            throw new RuntimeException("Failure from system", e);
        }
        return null;
   //...省略部分代码

代码调用了ActivityTaskManager的getService方法，让我们看下里面的逻辑处理

frameworks\base\core\java\android\app\ActivityTaskManager.java

	/** @hide */
    public static IActivityTaskManager getService() {
        return IActivityTaskManagerSingleton.get();
    }

    @UnsupportedAppUsage(trackingBug = 129726065)
    private static final Singleton<IActivityTaskManager> IActivityTaskManagerSingleton =
            new Singleton<IActivityTaskManager>() {
                @Override
                protected IActivityTaskManager create() {
                    final IBinder b = ServiceManager.getService(Context.ACTIVITY_TASK_SERVICE);
                    return IActivityTaskManager.Stub.asInterface(b);
                }
            };

(关于Singleton类的讲解可以参考我的这篇文章Android源码随心看系列：Singleton)
通过代码可以看出getService是获取了IActivityTaskManager.aidl接口，那么是哪个类实现了这个接口呢？答案是ActivityTaskManangerService。代码如下：

frameworks\base\services\core\java\com\android\server\wm\ActivityTaskManagerService.java

// ActivityTaskManagerService继承IActivityTaskManager.Stub
// IActivityTaskManager.Stub是Android根据aidl文件生成的java代码
public class ActivityTaskManagerService extends IActivityTaskManager.Stub {
    private static final String TAG = TAG_WITH_CLASS_NAME ? "ActivityTaskManagerService" : TAG_ATM;
    private static final String TAG_STACK = TAG + POSTFIX_STACK;
    private static final String TAG_SWITCH = TAG + POSTFIX_SWITCH;
    private static final String TAG_IMMERSIVE = TAG + POSTFIX_IMMERSIVE;
    private static final String TAG_FOCUS = TAG + POSTFIX_FOCUS;
    private static final String TAG_VISIBILITY = TAG + POSTFIX_VISIBILITY;
    private static final String TAG_LOCKTASK = TAG + POSTFIX_LOCKTASK;
    private static final String TAG_CONFIGURATION = TAG + POSTFIX_CONFIGURATION;
    //...省略部分代码
    int startActivityAsUser(IApplicationThread caller, String callingPackage,
            Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode,
            int startFlags, ProfilerInfo profilerInfo, Bundle bOptions, int userId,
            boolean validateIncomingUser) {
        enforceNotIsolatedCaller("startActivityAsUser");

        userId = getActivityStartController().checkTargetUser(userId, validateIncomingUser,
                Binder.getCallingPid(), Binder.getCallingUid(), "startActivityAsUser");

        // TODO: Switch to user app stacks here.
        return getActivityStartController().obtainStarter(intent, "startActivityAsUser")
                .setCaller(caller)
                .setCallingPackage(callingPackage)
                .setResolvedType(resolvedType)
                .setResultTo(resultTo)
                .setResultWho(resultWho)
                .setRequestCode(requestCode)
                .setStartFlags(startFlags)
                .setProfilerInfo(profilerInfo)
                .setActivityOptions(bOptions)
                .setMayWait(userId)
                .execute();

    }
    //...省略部分代码

最后调用的是ActivityTaskManagerService中的startActivityAsUser方法。通过分析可以知道了IActivityTaskManager.aidl就是Activity和ActivityTaskManagerService之间的桥梁。Activity的startActivity最终是调用了ActivityTaskManagerService中的startActivityAsUser方法

简化流程示意图：
Activity .java$\stackrel{IActivityTaskManager.aidl}{}$ActivityTaskManagerService.java

2.基于Android10以下的IPC

以上讲的是基于Android10的IPC，低于Android10的版本的IPC在细节上有些不一样，但是本质上是相同的。
还是回到execStartActivity方法：

frameworks\base\core\java\android\app\Instrumentation.java

    public ActivityResult execStartActivity(
            Context who, IBinder contextThread, IBinder token, Activity target,
            Intent intent, int requestCode, Bundle options) {
        ...
        try {
            intent.migrateExtraStreamToClipData();
            intent.prepareToLeaveProcess(who);
            // 重要代码
            int result = ActivityManager.getService()
                .startActivity(whoThread, who.getBasePackageName(), intent,
                        intent.resolveTypeIfNeeded(who.getContentResolver()),
                        token, target != null ? target.mEmbeddedID : null,
                        requestCode, 0, null, options);
            checkStartActivityResult(result, intent);
        } catch (RemoteException e) {
            throw new RuntimeException("Failure from system", e);
        }
        return null;
    }

老版本用的是ActivityManager类，但是代码结构和Android10的ActivityTaskManager是一致。

ActivityManager：

platform\frameworks_base\core\java\android\app\ActivityManager.java

	/**
     * @hide
     */
    @UnsupportedAppUsage
    public static IActivityManager getService() {
        return IActivityManagerSingleton.get();
    }

    private static IActivityTaskManager getTaskService() {
        return ActivityTaskManager.getService();
    }

    @UnsupportedAppUsage
    private static final Singleton<IActivityManager> IActivityManagerSingleton =
            new Singleton<IActivityManager>() {
                @Override
                protected IActivityManager create() {
                // 这里的IBinder其实是IActivityManager.aidl接口
                    final IBinder b = ServiceManager.getService(Context.ACTIVITY_SERVICE);
                    final IActivityManager am = IActivityManager.Stub.asInterface(b);
                    return am;
                }
            };

老版本用的是IActivityManager.aidl做IPC通讯的。大名鼎鼎的ActivityManagerService继承IActivityManger.aidl接口。所以老版本(Android 8.0及其以上)用IActivityManger做为IPC接口

简化流程示意图：
Activity .java$\stackrel{IActivityManager.aidl}{}$ActivityManagerService.java

下一篇：Activity启动源码分析-基于Android10(三)

参考文章：Activity的启动流程-基于Android10源码