startActivity启动过程分析

于 2024-03-18 17:09:39 发布
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文章标签： restful 后端
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本文链接：https://blog.youkuaiyun.com/a546036242/article/details/136815071
版权 
frameworks/base/services/core/java/com/android/server/am/
  - ActivityManagerService.java
  - ActivityStackSupervisor.java
  - ActivityStack.java
  - ActivityRecord.java
  - ProcessRecord.java

frameworks/base/core/java/android/app/
  - IActivityManager.java
  - ActivityManagerNative.java (内含AMP)
  - ActivityManager.java

  - IApplicationThread.java
  - ApplicationThreadNative.java (内含ATP)
  - ActivityThread.java (内含ApplicationThread)

  - ContextImpl.java

一. 概述

startActivity的整体流程与startService启动过程分析非常相近，但比Service启动更为复杂，多了stack/task以及UI的相关内容以及Activity的生命周期更为丰富。

Activity启动发起后，通过Binder最终交由system进程中的AMS来完成，则启动流程如下图：

start_activity

接下来，从源码来说说每个过程。

二. 启动流程

2.1 Activity.startActivity

[-> Activity.java]

public void startActivity(Intent intent) {
    this.startActivity(intent, null);
}

public void startActivity(Intent intent, @Nullable Bundle options) {
    if (options != null) {
        startActivityForResult(intent, -1, options);
    } else {
        //[见小节2.2]
        startActivityForResult(intent, -1);
    }
}

2.2 startActivityForResult

[-> Activity.java]

public void startActivityForResult(Intent intent, int requestCode) {
    startActivityForResult(intent, requestCode, null);
}

public void startActivityForResult(Intent intent, int requestCode, @Nullable Bundle options) {
    if (mParent == null) {
        //[见小节2.3]
        Instrumentation.ActivityResult ar =
            mInstrumentation.execStartActivity(
                this, mMainThread.getApplicationThread(), mToken, this,
                intent, requestCode, options);
        if (ar != null) {
            mMainThread.sendActivityResult(
                mToken, mEmbeddedID, requestCode, ar.getResultCode(),
                ar.getResultData());
        }
        //此时requestCode =-1
        if (requestCode >= 0) {
            mStartedActivity = true;
        }
        cancelInputsAndStartExitTransition(options);
    } else {
        ...
    }
}

execStartActivity()方法的参数:

  • mAppThread: 数据类型为ApplicationThread，通过mMainThread.getApplicationThread()方法获取。
  • mToken: 数据类型为IBinder.

2.3 execStartActivity

[-> Instrumentation.java]

public ActivityResult execStartActivity( Context who, IBinder contextThread, IBinder token, Activity target, Intent intent, int requestCode, Bundle options) {

    IApplicationThread whoThread = (IApplicationThread) contextThread;
    ...

    if (mActivityMonitors != null) {
        synchronized (mSync) {
            final int N = mActivityMonitors.size();
            for (int i=0; i<N; i++) {
                final ActivityMonitor am = mActivityMonitors.get(i);
                if (am.match(who, null, intent)) {
                    am.mHits++;
                    //当该monitor阻塞activity启动,则直接返回
                    if (am.isBlocking()) {
                        return requestCode >= 0 ? am.getResult() : null;
                    }
                    break;
                }
            }
        }
    }
    try {
        intent.migrateExtraStreamToClipData();
        intent.prepareToLeaveProcess();
        //[见小节2.4]
        int result = ActivityManagerNative.getDefault()
            .startActivity(whoThread, who.getBasePackageName(), intent,
                    intent.resolveTypeIfNeeded(who.getContentResolver()),
                    token, target != null ? target.mEmbeddedID : null,
                    requestCode, 0, null, options);
        //检查activity是否启动成功
        checkStartActivityResult(result, intent);
    } catch (RemoteException e) {
        throw new RuntimeException("Failure from system", e);
    }
    return null;
}

关于 ActivityManagerNative.getDefault()返回的是ActivityManagerProxy对象. 此处startActivity()的共有10个参数, 下面说说每个参数传递AMP.startActivity()每一项的对应值:

  • caller: 当前应用的ApplicationThread对象mAppThread;
  • callingPackage: 调用当前ContextImpl.getBasePackageName(),获取当前Activity所在包名;
  • intent: 这便是启动Activity时,传递过来的参数;
  • resolvedType: 调用intent.resolveTypeIfNeeded而获取;
  • resultTo: 来自于当前Activity.mToken
  • resultWho: 来自于当前Activity.mEmbeddedID
  • requestCode = -1;
  • startFlags = 0;
  • profilerInfo = null;
  • options = null;

2.4 AMP.startActivity

[-> ActivityManagerNative.java :: ActivityManagerProxy]

class ActivityManagerProxy implements IActivityManager {
    ...
    public int startActivity(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle options) throws RemoteException {
        Parcel data = Parcel.obtain();
        Parcel reply = Parcel.obtain();
        data.writeInterfaceToken(IActivityManager.descriptor);
        data.writeStrongBinder(caller != null ? caller.asBinder() : null);
        data.writeString(callingPackage);
        intent.writeToParcel(data, 0);
        data.writeString(resolvedType);
        data.writeStrongBinder(resultTo);
        data.writeString(resultWho);
        data.writeInt(requestCode);
        data.writeInt(startFlags);
        if (profilerInfo != null) {
            data.writeInt(1);
            profilerInfo.writeToParcel(data, Parcelable.PARCELABLE_WRITE_RETURN_VALUE);
        } else {
            data.writeInt(0);
        }
        if (options != null) {
            data.writeInt(1);
            options.writeToParcel(data, 0);
        } else {
            data.writeInt(0);
        }
        //[见流程2.5]
        mRemote.transact(START_ACTIVITY_TRANSACTION, data, reply, 0);
        reply.readException();
        int result = reply.readInt();
        reply.recycle();
        data.recycle();
        return result;
    }
    ...
}

AMP经过binder IPC,进入ActivityManagerNative(简称AMN)。接下来程序进入了system_servr进程，开始继续执行。

2.5 AMN.onTransact

[-> ActivityManagerNative.java]

public boolean onTransact(int code, Parcel data, Parcel reply, int flags) throws RemoteException {
    switch (code) {
    case START_ACTIVITY_TRANSACTION:
    {
      data.enforceInterface(IActivityManager.descriptor);
      IBinder b = data.readStrongBinder();
      IApplicationThread app = ApplicationThreadNative.asInterface(b);
      String callingPackage = data.readString();
      Intent intent = Intent.CREATOR.createFromParcel(data);
      String resolvedType = data.readString();
      IBinder resultTo = data.readStrongBinder();
      String resultWho = data.readString();
      int requestCode = data.readInt();
      int startFlags = data.readInt();
      ProfilerInfo profilerInfo = data.readInt() != 0
              ? ProfilerInfo.CREATOR.createFromParcel(data) : null;
      Bundle options = data.readInt() != 0
              ? Bundle.CREATOR.createFromParcel(data) : null;
      //[见流程2.6]
      int result = startActivity(app, callingPackage, intent, resolvedType,
              resultTo, resultWho, requestCode, startFlags, profilerInfo, options);
      reply.writeNoException();
      reply.writeInt(result);
      return true;
    }
    ...
    }    }

2.6 AMS.startActivity

[-> ActivityManagerService.java]

public final int startActivity(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle options) {
    return startActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
        resultWho, requestCode, startFlags, profilerInfo, options,
        UserHandle.getCallingUserId());
}

public final int startActivityAsUser(IApplicationThread caller, String callingPackage, Intent intent, String resolvedType, IBinder resultTo, String resultWho, int requestCode, int startFlags, ProfilerInfo profilerInfo, Bundle options, int userId) {
    enforceNotIsolatedCaller("startActivity");
    userId = handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(), userId,
            false, ALLOW_FULL_ONLY, "startActivity", null);
    //[见小节2.7]
    return mStackSupervisor.startActivityMayWait(caller, -1, callingPackage, intent,
            resolvedType, null, null, resultTo, resultWho, requestCode, startFlags,
            profilerInfo, null, null, options, false, userId, null, null);
}

此处mStackSupervisor的数据类型为ActivityStackSupervisor

2.7 ASS.startActivityMayWait

当程序运行到这里时, ASS.startActivityMayWait的各个参数取值如下:

  • caller = ApplicationThreadProxy, 用于跟调用者进程ApplicationThread进行通信的binder代理类.
  • callingUid = -1;
  • callingPackage = ContextImpl.getBasePackageName(),获取调用者Activity所在包名
  • intent: 这是启动Activity时传递过来的参数;
  • resolvedType = intent.resolveTypeIfNeeded
  • voiceSession = null;
  • voiceInteractor = null;
  • resultTo = Activity.mToken, 其中Activity是指调用者所在Activity, mToken对象保存自己所处的ActivityRecord信息
  • resultWho = Activity.mEmbeddedID, 其中Activity是指调用者所在Activity
  • requestCode = -1;
  • startFlags = 0;
  • profilerInfo = null;
  • outResult = null;
  • config = null;
  • options = null;
  • ignoreTargetSecurity = false;
  • userId = AMS.handleIncomingUser, 当调用者userId跟当前处于同一个userId,则直接返回该userId;当不相等时则根据调用者userId来决定是否需要将callingUserId转换为mCurrentUserId.
  • iContainer = null;
  • inTask = null;

再来看看这个方法的源码:

[-> ActivityStackSupervisor.java]

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 config, Bundle options, boolean ignoreTargetSecurity, int userId, IActivityContainer iContainer, TaskRecord inTask) {
    ...
    boolean componentSpecified = intent.getComponent() != null;
    //创建新的Intent对象，即便intent被修改也不受影响
    intent = new Intent(intent);

    //收集Intent所指向的Activity信息, 当存在多个可供选择的Activity,则直接向用户弹出resolveActivity [见2.7.1]
    ActivityInfo aInfo = resolveActivity(intent, resolvedType, startFlags, profilerInfo, userId);

    ActivityContainer container = (ActivityContainer)iContainer;
    synchronized (mService) {
        if (container != null && container.mParentActivity != null &&
                container.mParentActivity.state != RESUMED) {
            ... //不进入该分支, container == nul
        }

        final int realCallingPid = Binder.getCallingPid();
        final int realCallingUid = Binder.getCallingUid();
        int callingPid;
        if (callingUid >= 0) {
            callingPid = -1;
        } else if (caller == null) {
            callingPid = realCallingPid;
            callingUid = realCallingUid;
        } else {
            callingPid = callingUid = -1;
        }

        final ActivityStack stack;
        if (container == null || container.mStack.isOnHomeDisplay()) {
            stack = mFocusedStack; // 进入该分支
        } else {
            stack = container.mStack;
        }

        //此时mConfigWillChange = false
        stack.mConfigWillChange = config != null && mService.mConfiguration.diff(config) != 0;

        final long origId = Binder.clearCallingIdentity();

        if (aInfo != null &&
                (aInfo.applicationInfo.privateFlags
                        &ApplicationInfo.PRIVATE_FLAG_CANT_SAVE_STATE) != 0) {
            // heavy-weight进程处理流程, 一般情况下不进入该分支
            if (aInfo.processName.equals(aInfo.applicationInfo.packageName)) {
                ...
            }
        }

        //[见流程2.8]
        int res = startActivityLocked(caller, intent, resolvedType, aInfo,
                voiceSession, voiceInteractor, resultTo, resultWho,
                requestCode, callingPid, callingUid, callingPackage,
                realCallingPid, realCallingUid, startFlags, options, ignoreTargetSecurity,
                componentSpecified, null, container, inTask);

        Binder.restoreCallingIdentity(origId);

        if (stack.mConfigWillChange) {
            ... //不进入该分支
        }

        if (outResult != null) {
            ... //不进入该分支
        }

        return res;
    }
}

该过程主要功能：通过resolveActivity来获取ActivityInfo信息, 然后再进入ASS.startActivityLocked().先来看看

2.7.1 ASS.resolveActivity
// startFlags = 0; profilerInfo = null; userId代表caller UserId
ActivityInfo resolveActivity(Intent intent, String resolvedType, int startFlags, ProfilerInfo profilerInfo, int userId) {
    ActivityInfo aInfo;
    ResolveInfo rInfo =
        AppGlobals.getPackageManager().resolveIntent(
                intent, resolvedType,
                PackageManager.MATCH_DEFAULT_ONLY
                            | ActivityManagerService.STOCK_PM_FLAGS, userId);
    aInfo = rInfo != null ? rInfo.activityInfo : null;
    if (aInfo != null) {
        intent.setComponent(new ComponentName(
                aInfo.applicationInfo.packageName, aInfo.name));

        if (!aInfo.processName.equals("system")) {
            ... //对于非system进程，根据flags来设置相应的debug信息
        }
    }
    return aInfo;
}

ActivityManager类有如下4个flags用于调试：

  • START_FLAG_DEBUG：用于调试debug app
  • START_FLAG_OPENGL_TRACES：用于调试OpenGL tracing
  • START_FLAG_NATIVE_DEBUGGING：用于调试native
  • START_FLAG_TRACK_ALLOCATION: 用于调试allocation tracking
2.7.2 PKMS.resolveIntent

AppGlobals.getPackageManager()经过函数层层调用，获取的是ApplicationPackageManager对象。经过binder IPC调用，最终会调用PackageManagerService对象。故此时调用方法为PMS.resolveIntent().

[-> PackageManagerService.java]

public ResolveInfo resolveIntent(Intent intent, String resolvedType, int flags, int userId) {
     if (!sUserManager.exists(userId)) return null;
     enforceCrossUserPermission(Binder.getCallingUid(), userId, false, false, "resolve intent");
     //[见流程2.7.3]
     List<ResolveInfo> query = queryIntentActivities(intent, resolvedType, flags, userId);
     //根据priority，preferred选择最佳的Activity
     return chooseBestActivity(intent, resolvedType, flags, query, userId);
 }
2.7.3 PMS.queryIntentActivities
public List<ResolveInfo> queryIntentActivities(Intent intent,
        String resolvedType, int flags, int userId) {
    ...
    ComponentName comp = intent.getComponent();
    if (comp == null) {
        if (intent.getSelector() != null) {
            intent = intent.getSelector();
            comp = intent.getComponent();
        }
    }

    if (comp != null) {
        final List<ResolveInfo> list = new ArrayList<ResolveInfo>(1);
        //获取Activity信息
        final ActivityInfo ai = getActivityInfo(comp, flags, userId);
        if (ai != null) {
            final ResolveInfo ri = new ResolveInfo();
            ri.activityInfo = ai;
            list.add(ri);
        }
        return list;
    }
    ...
}

ASS.resolveActivity()方法的核心功能是找到相应的Activity组件，并保存到intent对象。

2.8 ASS.startActivityLocked

[-> ActivityStackSupervisor.java]

final int startActivityLocked(IApplicationThread caller,

Intent intent, String resolvedType, ActivityInfo aInfo,
IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
IBinder resultTo, String resultWho, int requestCode,
int callingPid, int callingUid, String callingPackage,
int realCallingPid, int realCallingUid, int startFlags, Bundle options,
boolean ignoreTargetSecurity, boolean componentSpecified, ActivityRecord[] outActivity,
ActivityContainer container, TaskRecord inTask) { int err = ActivityManager.START_SUCCESS;

    //获取调用者的进程记录对象
    ProcessRecord callerApp = null;
    if (caller != null) {
        callerApp = mService.getRecordForAppLocked(caller);
        if (callerApp != null) {
            callingPid = callerApp.pid;
            callingUid = callerApp.info.uid;
        } else {
            err = ActivityManager.START_PERMISSION_DENIED;
        }
    }

    final in
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