Android10 Android Input系统

Android10 输入输出系统UI主线程分析

本篇博文我们来学习下输入输出系统在UI主线程中都有哪些相关的业务逻辑

发布日期 2020-11-18

一. 概述

前面文章都是介绍了两个线程InputReader和InputDispatcher的工作过程。在InputDispatcher的过程讲到 调用InputChanel通过socket与远程进程通信，本文便展开讲解这个socket是如何建立的。

对于InputReader和InputDispatcher都是运行在system_server进程； 用户点击的界面往往可能是某一个app，而每个app一般地都运行在自己的进程，这里就涉及到跨进程通信，app进程是如何与system进程建立通信。

要解答这些问题，从Activity最基本的创建过程开始说起。我们都知道一般地Activity对应一个应用窗口, 每一个窗口对应一个ViewRootImpl。窗口是如何添加到Activity的，从Activity.onCreate()为起点讲解。

二. UI线程

众所周知，Activity的生命周期的回调方法都是运行在主线程，也称之为UI线程，所有UI相关的操作都需要运行在该线程。本文虽然是UI线程，但并非只介绍所有运行在UI线程的流程，文中还涉及binder thread。

2.1 onCreate

[-> Activity.java]

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_account_bind);
    ...
}

Activity启动是由system进程控制：

  1. handleLaunchActivity()：会调用Activity.onCreate(), 该方法内再调用setContentView(),经过AMS与WMS的各种交互,层层调用后,进入step2
  2. handleResumeActivity()：会调用Activity.makeVisible(),该方法继续调用便会执行到WindowManagerImpl.addView(), 该方法内部再调用WindowManagerGlobal.addView(),

2.2 addView

[-> WindowManagerGlobal.java]

public void addView(View view, ViewGroup.LayoutParams params,
        Display display, Window parentWindow) {
    ...
    //[见小节2.3]
    ViewRootImpl root = new ViewRootImpl(view.getContext(), display);
    //[见小节2.3.3]
    root.setView(view, wparams, panelParentView);
    ...
}

2.3 ViewRootImpl

[-> ViewRootImpl.java]

public ViewRootImpl(Context context, Display display) {
    mContext = context;
    //获取IWindowSession的代理类【见小节2.3.1】
    mWindowSession = WindowManagerGlobal.getWindowSession();
    mDisplay = display;
    mThread = Thread.currentThread(); //主线程
    mWindow = new W(this);
    mChoreographer = Choreographer.getInstance();
    ...
}

2.3.1 getWindowSession

[-> WindowManagerGlobal.java]

public static IWindowSession getWindowSession() {
    synchronized (WindowManagerGlobal.class) {
        if (sWindowSession == null) {
            try {
                //获取IMS的代理类
                InputMethodManager imm = InputMethodManager.getInstance();
                //获取WMS的代理类
                IWindowManager windowManager = getWindowManagerService();
                //经过Binder调用，最终调用WMS[见小节2.3.2]
                sWindowSession = windowManager.openSession(
                        new IWindowSessionCallback.Stub() {...},
                        imm.getClient(), imm.getInputContext());
            } catch (RemoteException e) {
                ...
            }
        }
        return sWindowSession
    }
}

2.3.2 WMS.openSession

public IWindowSession openSession(IWindowSessionCallback callback, IInputMethodClient client,
        IInputContext inputContext) {
    //创建Session对象
    Session session = new Session(this, callback, client, inputContext);
    return session;
}

再次经过Binder将数据写回app进程，则获取的便是Session的代理对象。

2.3.3 setView

[-> ViewRootImpl.java]

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
    synchronized (this) {
      ...
      if ((mWindowAttributes.inputFeatures
          & WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
          mInputChannel = new InputChannel(); //创建InputChannel对象
      }
      //通过Binder调用，进入system进程的Session[见小节2.4]
      res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                  getHostVisibility(), mDisplay.getDisplayId(),
                  mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
                  mAttachInfo.mOutsets, mInputChannel);
      ...
      if (mInputChannel != null) {
          if (mInputQueueCallback != null) {
              mInputQueue = new InputQueue();
              mInputQueueCallback.onInputQueueCreated(mInputQueue);
          }
          //创建WindowInputEventReceiver对象[见3.1]
          mInputEventReceiver = new WindowInputEventReceiver(mInputChannel,
                  Looper.myLooper());
      }
    }
}

该方法主要功能:

  1. 创建Java层的InputChannel对象mInputChannel
  2. 向WMS注册InputChannel信息，通过InputChannel.openInputChannelPair创建的socket pair，将其中的客户端赋值给mInputChannel.
  3. 创建WindowInputEventReceiver对象

跨进程调用，进入binder thread执行如下方法：

2.4 Session.addToDisplay

[-> Session.java]

final class Session extends IWindowSession.Stub implements IBinder.DeathRecipient {

    public int addToDisplay(IWindow window, int seq, WindowManager.LayoutParams attrs,
            int viewVisibility, int displayId, Rect outContentInsets, Rect outStableInsets,
            Rect outOutsets, InputChannel outInputChannel) {
        //[见小节2.5]
        return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId,
                outContentInsets, outStableInsets, outOutsets, outInputChannel);
    }
}

2.5 WMS.addToDisplay

[-> WindowManagerService.java]

public int addWindow(Session session, IWindow client, int seq,
           WindowManager.LayoutParams attrs, int viewVisibility, int displayId,
           Rect outContentInsets, Rect outStableInsets, Rect outOutsets,
           InputChannel outInputChannel) {
    ...
    //创建WindowState【见小节2.5.1】
    WindowState win = new WindowState(this, session, client, token,
                attachedWindow, appOp[0], seq, attrs, viewVisibility, displayContent);
                
    if (outInputChannel != null && (attrs.inputFeatures
            & WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
         //根据WindowState的HashCode以及title来生成InputChannel名称
        String name = win.makeInputChannelName();
        
        //创建一对InputChannel[见小节2.6]
        InputChannel[] inputChannels = InputChannel.openInputChannelPair(name);
        //将socket服务端保存到WindowState的mInputChannel
        win.setInputChannel(inputChannels[0]);
        
        //socket客户端传递给outInputChannel [见小节2.7]
        inputChannels[1].transferTo(outInputChannel);
        //利用socket服务端作为参数[见小节2.8]
        mInputManager.registerInputChannel(win.mInputChannel, win.mInputWindowHandle);
    }
    ...
    boolean focusChanged = false;
    if (win.canReceiveKeys()) {
        //新添加window能接收按下操作，则更新聚焦窗口。
        focusChanged = updateFocusedWindowLocked(UPDATE_FOCUS_WILL_ASSIGN_LAYERS,
                false /*updateInputWindows*/);
    }
    ...
    
    if (focusChanged) {
        mInputMonitor.setInputFocusLw(mCurrentFocus, false /*updateInputWindows*/);
    }
    //设置当前聚焦窗口【见小节2.5.2】
    mInputMonitor.updateInputWindowsLw(false /*force*/);
}

inputChannels数组：

  • inputChannels[0]所对应的InputChannel名称的后缀为(server);
  • inputChannels[1]所对应的InputChannel名称的后缀为(client)；

其中：

  • 服务端inputChannels[0]保存到WindowState的mInputChannel；
  • 客户端inputChannels[1]传递给outInputChannel，最终传递给ViewRootImpl的mInputChannel；

2.5.1 WindowState初始化

[-> WindowState.java]

WindowState(WindowManagerService service, Session s, IWindow c, WindowToken token,
       WindowState attachedWindow, int appOp, int seq, WindowManager.LayoutParams a,
       int viewVisibility, final DisplayContent displayContent) {
    ...
    WindowState appWin = this;
    while (appWin.mAttachedWindow != null) {
       appWin = appWin.mAttachedWindow;
    }
    WindowToken appToken = appWin.mToken;
    while (appToken.appWindowToken == null) {
       WindowToken parent = mService.mTokenMap.get(appToken.token);
       if (parent == null || appToken == parent) {
           break;
       }
       appToken = parent;
    }
    mAppToken = appToken.appWindowToken;
    //创建InputWindowHandle对象
    mInputWindowHandle = new InputWindowHandle(
            mAppToken != null ? mAppToken.mInputApplicationHandle : null, this,
            displayContent.getDisplayId());
}

2.5.2 updateInputWindowsLw

[-> InputMonitor.java]

public void updateInputWindowsLw(boolean force) {
    ...
    final InputWindowHandle dragWindowHandle = mService.mDragState.mDragWindowHandle;
    if (dragWindowHandle != null) {
        //将dragWindowHandle赋值给mInputWindowHandles
        addInputWindowHandleLw(dragWindowHandle);
    } 
    ...
    //将当前mInputWindowHandles传递到native【】
    mService.mInputManager.setInputWindows(mInputWindowHandles);
    ...
}

setInputWindows的调用链：(最终设置mFocusedWindowHandle值)

-> IMS.setInputWindows 
  -> NativeInputManager::setInputWindows
    -> InputDispatcher::setInputWindows

dragWindowHandle的初始化过程：

View.startDrag
    Session.prepareDrag
      WMS.prepareDragSurface
        mDragState = new DragState(...);
    Session.performDrag   
      DragState.register
        mDragWindowHandle = new InputWindowHandle(...);

2.6 openInputChannelPair

[-> InputChannel.java]

public static InputChannel[] openInputChannelPair(String name) {
    return nativeOpenInputChannelPair(name);
}

这个过程的主要功能

  1. 创建两个socket通道(非阻塞, buffer上限32KB)
  2. 创建两个InputChannel对象;
  3. 创建两个NativeInputChannel对象;
  4. 将nativeInputChannel保存到Java层的InputChannel的成员变量mPtr

2.6.1 nativeOpenInputChannelPair

[-> android_view_InputChannel.cpp]

static jobjectArray android_view_InputChannel_nativeOpenInputChannelPair(JNIEnv* env,
        jclass clazz, jstring nameObj) {
    const char* nameChars = env->GetStringUTFChars(nameObj, NULL);
    String8 name(nameChars);
    env->ReleaseStringUTFChars(nameObj, nameChars);

    sp<InputChannel> serverChannel;
    sp<InputChannel> clientChannel;
    //创建一对socket[见小节2.6.2]
    status_t result = InputChannel::openInputChannelPair(name, serverChannel, clientChannel);

    //创建Java数组
    jobjectArray channelPair = env->NewObjectArray(2, gInputChannelClassInfo.clazz, NULL);
    ...

    //创建NativeInputChannel对象[见小节2.6.3]
    jobject serverChannelObj = android_view_InputChannel_createInputChannel(env,
            new NativeInputChannel(serverChannel));
    ...
    
    //创建NativeInputChannel对象[见小节2.6.3]
    jobject clientChannelObj = android_view_InputChannel_createInputChannel(env,
            new NativeInputChannel(clientChannel));
    ...
    
    //将client和server 两个插入到channelPair
    env->SetObjectArrayElement(channelPair, 0, serverChannelObj);
    env->SetObjectArrayElement(channelPair, 1, clientChannelObj);
    return channelPair;
}

2.6.2 openInputChannelPair

[-> InputTransport.cpp]

status_t InputChannel::openInputChannelPair(const String8& name,
        sp<InputChannel>& outServerChannel, sp<InputChannel>& outClientChannel) {
    int sockets[2];
    //真正创建socket对的地方【核心】
    if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sockets)) {
        ...
        return result;
    }

    int bufferSize = SOCKET_BUFFER_SIZE; //32k
    setsockopt(sockets[0], SOL_SOCKET, SO_SNDBUF, &bufferSize, sizeof(bufferSize));
    setsockopt(sockets[0], SOL_SOCKET, SO_RCVBUF, &bufferSize, sizeof(bufferSize));
    setsockopt(sockets[1], SOL_SOCKET, SO_SNDBUF, &bufferSize, sizeof(bufferSize));
    setsockopt(sockets[1], SOL_SOCKET, SO_RCVBUF, &bufferSize, sizeof(bufferSize));

    String8 serverChannelName = name;
    serverChannelName.append(" (server)");
    //创建InputChannel对象
    outServerChannel = new InputChannel(serverChannelName, sockets[0]);

    String8 clientChannelName = name;
    clientChannelName.append(" (client)");
    //创建InputChannel对象
    outClientChannel = new InputChannel(clientChannelName, sockets[1]);
    return OK;
}

该方法主要功能:

  1. 创建socket pair; (非阻塞式的socket)
  2. 设置两个socket的接收和发送的buffer上限为32KB;
  3. 创建client和server的Native层InputChannel对象;
    • sockets[0]所对应的InputChannel名称的后缀为(server);
    • sockets[1]所对应的InputChannel名称的后缀为(client)

创建InputChannel对象位于文件InputTransport.cpp，如下：

InputChannel::InputChannel(const String8& name, int fd) :
        mName(name), mFd(fd) {
    //将socket设置成非阻塞方式
    int result = fcntl(mFd, F_SETFL, O_NONBLOCK);
}

另外，创建NativeInputChannel对象位于文件android_view_InputChannel.cpp，如下：

NativeInputChannel::NativeInputChannel(const sp<InputChannel>& inputChannel) :
  mInputChannel(inputChannel), mDisposeCallback(NULL) {
}

2.6.3 android_view_InputChannel_createInputChannel

[-> android_view_InputChannel.cpp]

static jobject android_view_InputChannel_createInputChannel(JNIEnv* env,
        NativeInputChannel* nativeInputChannel) {
    //创建Java的InputChannel
    jobject inputChannelObj = env->NewObject(gInputChannelClassInfo.clazz,
            gInputChannelClassInfo.ctor);
    if (inputChannelObj) {
        //将nativeInputChannel保存到Java层的InputChannel的成员变量mPtr
        android_view_InputChannel_setNativeInputChannel(env, inputChannelObj, nativeInputChannel);
    }
    return inputChannelObj;
}

static void android_view_InputChannel_setNativeInputChannel(JNIEnv* env, jobject inputChannelObj,
        NativeInputChannel* nativeInputChannel) {
    env->SetLongField(inputChannelObj, gInputChannelClassInfo.mPtr,
             reinterpret_cast<jlong>(nativeInputChannel));
}

此处:

  • gInputChannelClassInfo.clazz是指Java层的InputChannel类
  • gInputChannelClassInfo.ctor是指Java层的InputChannel构造方法;
  • gInputChannelClassInfo.mPtr是指Java层的InputChannel的成员变量mPtr;

2.7 transferTo

[-> InputChannel.java]

public void transferTo(InputChannel outParameter) {    
    nativeTransferTo(outParameter);
}

2.7.1 nativeTransferTo

[-> android_view_InputChannel.cpp]

static void android_view_InputChannel_nativeTransferTo(JNIEnv* env, jobject obj,
        jobject otherObj) {
    
    if (android_view_InputChannel_getNativeInputChannel(env, otherObj) != NULL) {
        return; //当Java层的InputChannel.mPtr不为空,则返回
    }
    
    //将当前inputChannels[1]的mPtr赋值给nativeInputChannel
    NativeInputChannel* nativeInputChannel =
            android_view_InputChannel_getNativeInputChannel(env, obj);
    // 将该nativeInputChannel保存到outInputChannel的参数
    android_view_InputChannel_setNativeInputChannel(env, otherObj, nativeInputChannel);
    android_view_InputChannel_setNativeInputChannel(env, obj, NULL);
}

inputChannels[1].transferTo(outInputChannel)主要功能:

  1. 当outInputChannel.mPtr不为空,则直接返回;否则进入step2;
  2. 将inputChannels[1].mPtr的值赋给outInputChannel.mPtr;
  3. 清空inputChannels[1].mPtr值;

也就是将socket客户端inputChannels[1]传递给outInputChannel；

2.8 IMS.registerInputChannel

[-> InputManagerService.java]

public void registerInputChannel(InputChannel inputChannel,
        InputWindowHandle inputWindowHandle) {
    nativeRegisterInputChannel(mPtr, inputChannel, inputWindowHandle, false);
}
  • inputChannel是指inputChannels[0],即socket服务端；
  • inputWindowHandle是指WindowState.mInputWindowHandle;

2.8.1 nativeRegisterInputChannel

[-> com_android_server_input_InputManagerService.cpp]

static void nativeRegisterInputChannel(JNIEnv* env, jclass /* clazz */,
        jlong ptr, jobject inputChannelObj, jobject inputWindowHandleObj, jboolean monitor) {
    NativeInputManager* im = reinterpret_cast<NativeInputManager*>(ptr);

    sp<InputChannel> inputChannel = android_view_InputChannel_getInputChannel(env,
            inputChannelObj);

    sp<InputWindowHandle> inputWindowHandle =
            android_server_InputWindowHandle_getHandle(env, inputWindowHandleObj);
    
    //[见小节2.8.2]
    status_t status = im->registerInputChannel(
            env, inputChannel, inputWindowHandle, monitor);
    ...

    if (! monitor) {
        android_view_InputChannel_setDisposeCallback(env, inputChannelObj,
                handleInputChannelDisposed, im);
    }
}

2.8.2 registerInputChannel

[-> com_android_server_input_InputManagerService.cpp]

status_t NativeInputManager::registerInputChannel(JNIEnv* /* env */,
        const sp<InputChannel>& inputChannel,
        const sp<InputWindowHandle>& inputWindowHandle, bool monitor) {
    //[见小节2.8.3]
    return mInputManager->getDispatcher()->registerInputChannel(
            inputChannel, inputWindowHandle, monitor);
}

mInputManager是指NativeInputManager初始化过程创建的InputManager对象(C++).

2.8.3 registerInputChannel

[-> InputDispatcher.cpp]

status_t InputDispatcher::registerInputChannel(const sp<InputChannel>& inputChannel,
        const sp<InputWindowHandle>& inputWindowHandle, bool monitor) {
    { 
        AutoMutex _l(mLock);
        ...
        
        //创建Connection[见小节2.8.4]
        sp<Connection> connection = new Connection(inputChannel, inputWindowHandle, monitor);

        int fd = inputChannel->getFd();
        mConnectionsByFd.add(fd, connection);
        ...
        //将该fd添加到Looper监听[见小节2.8.5]
        mLooper->addFd(fd, 0, ALOOPER_EVENT_INPUT, handleReceiveCallback, this);
    }

    mLooper->wake(); //connection改变, 则唤醒looper
    return OK;
}

将新创建的connection保存到mConnectionsByFd成员变量，“InputDispatcher”线程的Looper添加对socket服务端的监听功能； 当该socket有消息时便会唤醒该线程工作。

2.8.4 初始化Connection

[-> InputDispatcher.cpp]

InputDispatcher::Connection::Connection(const sp<InputChannel>& inputChannel,
        const sp<InputWindowHandle>& inputWindowHandle, bool monitor) :
        status(STATUS_NORMAL), inputChannel(inputChannel), inputWindowHandle(inputWindowHandle),
        monitor(monitor),
        inputPublisher(inputChannel), inputPublisherBlocked(false) {
}

其中InputPublisher初始化位于文件InputTransport.cpp

InputPublisher:: InputPublisher(const sp<InputChannel>& channel) :
        mChannel(channel) {
}

此处inputChannel是指前面openInputChannelPair创建的socket服务端，将其同时保存到Connection.inputChannel和InputPublisher.mChannel。

2.8.5 Looper.addFd

[-> system/core/libutils/Looper.cpp]

int Looper::addFd(int fd, int ident, int events, Looper_callbackFunc callback, void* data) {
    // 此处的callback为handleReceiveCallback 
    return addFd(fd, ident, events, callback ? new SimpleLooperCallback(callback) : NULL, data);
}

int Looper::addFd(int fd, int ident, int events, const sp<LooperCallback>& callback, void* data) {
    {
        AutoMutex _l(mLock);
        Request request;
        request.fd = fd;
        request.ident = ident;
        request.events = events;
        request.seq = mNextRequestSeq++;
        request.callback = callback; //是指SimpleLooperCallback
        request.data = data;
        if (mNextRequestSeq == -1) mNextRequestSeq = 0;
        
        struct epoll_event eventItem;
        request.initEventItem(&eventItem);

        ssize_t requestIndex = mRequests.indexOfKey(fd);
        if (requestIndex < 0) {
            //通过epoll监听fd
            int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, & eventItem);
            ...
            mRequests.add(fd, request); //该fd的request加入到mRequests队列
        } else {
            int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_MOD, fd, & eventItem);
            ...
            mRequests.replaceValueAt(requestIndex, request);
        }
    } 
    return 1;
}

此处Loop便是“InputDispatcher”线程的Looper，将socket服务端的fd采用epoll机制注册监听.

小节

虽然本文介绍的UI线程的工作，

  • [小节2.1 ~ 2.3]： 运行在UI线程；
  • [小节2.4 ~ 2.8]：通过IWindowSession的Binder IPC调用，运行在system_server的binder thread;

ViewRootImpl的setView()过程:

  • 创建socket pair，作为InputChannel:
    • socket服务端保存到system_server中的WindowState的mInputChannel；
    • socket客户端通过binder传回到远程进程的UI主线程ViewRootImpl的mInputChannel；
  • IMS.registerInputChannel()注册InputChannel，监听socket服务端：
    • Loop便是“InputDispatcher”线程的Looper;
    • 回调方法handleReceiveCallback。

三. WindowInputEventReceiver

接下来，看看【小节2.3.3】创建WindowInputEventReceiver对象

3.1 WindowInputEventReceiver初始化

[-> ViewRootImpl.java]

final class WindowInputEventReceiver extends InputEventReceiver {
    //inputChannel是指socket客户端，Looper是指UI线程的Looper
    public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {
        super(inputChannel, looper); //【见小节3.2】
    }
    ...
}

3.2 InputEventReceiver

[-> InputEventReceiver.java]

public InputEventReceiver(InputChannel inputChannel, Looper looper) {
     ...
     mInputChannel = inputChannel;
     mMessageQueue = looper.getQueue(); //UI线程消息队列
     //【加小节3.3】
     mReceiverPtr = nativeInit(new WeakReference<InputEventReceiver>(this),
             inputChannel, mMessageQueue);
 }

3.3 nativeInit

[-> android_view_InputEventReceiver.cpp]

static jlong nativeInit(JNIEnv* env, jclass clazz, jobject receiverWeak,
        jobject inputChannelObj, jobject messageQueueObj) {
    sp<InputChannel> inputChannel = android_view_InputChannel_getInputChannel(env,
            inputChannelObj);
    //获取UI主线程的消息队列
    sp<MessageQueue> messageQueue = android_os_MessageQueue_getMessageQueue(env, messageQueueObj);
    //创建NativeInputEventReceiver对象【见小节3.4】
    sp<NativeInputEventReceiver> receiver = new NativeInputEventReceiver(env,
            receiverWeak, inputChannel, messageQueue);
    //【见小节3.5】
    status_t status = receiver->initialize();
    ...

    receiver->incStrong(gInputEventReceiverClassInfo.clazz); 
    return reinterpret_cast<jlong>(receiver.get());
}

3.4 NativeInputEventReceiver

[-> android_view_InputEventReceiver.cpp]

class NativeInputEventReceiver : public LooperCallback {
    InputConsumer mInputConsumer;
    sp<MessageQueue> mMessageQueue;
    int mFdEvents;
    bool mBatchedInputEventPending;
    ...
    
    NativeInputEventReceiver::NativeInputEventReceiver(JNIEnv* env,
            jobject receiverWeak, const sp<InputChannel>& inputChannel,
            const sp<MessageQueue>& messageQueue) :
            mReceiverWeakGlobal(env->NewGlobalRef(receiverWeak)),
            //【见3.4.1】
            mInputConsumer(inputChannel), mMessageQueue(messageQueue),
            mBatchedInputEventPending(false), mFdEvents(0) {
            
    }
}

3.4.1 InputConsumer

[-> InputTransport.cpp]

InputConsumer::InputConsumer(const sp<InputChannel>& channel) :
        mResampleTouch(isTouchResamplingEnabled()),
        mChannel(channel), mMsgDeferred(false) {
}

此处inputChannel是指socket客户端。

3.5 initialize

[-> android_view_InputEventReceiver.cpp]

status_t NativeInputEventReceiver::initialize() {
    setFdEvents(ALOOPER_EVENT_INPUT);  //【见小节3.6】
    return OK;
}

3.6 setFdEvents

[-> android_view_InputEventReceiver.cpp]

void NativeInputEventReceiver::setFdEvents(int events) {
  if (mFdEvents != events) {
      mFdEvents = events;
      int fd = mInputConsumer.getChannel()->getFd();
      if (events) {
          //将socket客户端的fd添加到主线程的消息池【见小节3.6.1】
          mMessageQueue->getLooper()->addFd(fd, 0, events, this, NULL);
      } else {
          mMessageQueue->getLooper()->removeFd(fd);
      }
  }
}

3.6.1 Looper.addFd

[-> system/core/libutils/Looper.cpp]

int Looper::addFd(int fd, int ident, int events, const sp<LooperCallback>& callback, void* data) {
    {
        AutoMutex _l(mLock);
        Request request;
        request.fd = fd;
        request.ident = ident;
        request.events = events;
        request.seq = mNextRequestSeq++;
        request.callback = callback; //是指ativeInputEventReceiver
        request.data = data;
        if (mNextRequestSeq == -1) mNextRequestSeq = 0;
        
        struct epoll_event eventItem;
        request.initEventItem(&eventItem);

        ssize_t requestIndex = mRequests.indexOfKey(fd);
        if (requestIndex < 0) {
            //通过epoll监听fd
            int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, fd, & eventItem);
            ...
            mRequests.add(fd, request); //该fd的request加入到mRequests队列
        } else {
            int epollResult = epoll_ctl(mEpollFd, EPOLL_CTL_MOD, fd, & eventItem);
            ...
            mRequests.replaceValueAt(requestIndex, request);
        }
    } 
    return 1;
}

此处的Looper便是UI主线程的Looper，将socket客户端的fd添加到UI线程的Looper来监听，回调方法为NativeInputEventReceiver。

四. 总结

input_ui

首先，通过openInputChannelPair来创建socket pair，作为InputChannel:

  • socket服务端保存到system_server中的WindowState的mInputChannel；
  • socket客户端通过binder传回到远程进程的UI主线程ViewRootImpl的mInputChannel；

紧接着，完成了两个线程的epoll监听工作：

  • [小节2.8]IMS.registerInputChannel(): “InputDispatcher”线程监听socket服务端，收到消息后回调InputDispatcher.handleReceiveCallback()；
  • [小节3.6]setFdEvents(): UI主线程监听socket客户端，收到消息后回调NativeInputEventReceiver.handleEvent().

有了这些“InputDispatcher”和“UI”主线程便可以进行跨进程通信与交互。

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