应用窗口与InputDispatcher之间的桥梁:InputChannel

InputDispatcher接收InputReader读取到的事件，分发给对应窗口，InputDispatcher属于system_server进程和各个应用不在同一进程，它们之间的联系靠的就是InputChannel。

handleResumeActivity

直接从ActivityThread的handleResumeActivity开始，Activity的DecorView会被添加到Window

    @Override
    public void handleResumeActivity(IBinder token, boolean finalStateRequest, boolean isForward,
            String reason) {
            ......
            if (a.mVisibleFromClient) {
                if (!a.mWindowAdded) {
                    a.mWindowAdded = true;
                    wm.addView(decor, l);
                } else { 
                    ......
                    a.onWindowAttributesChanged(l);
                }
            }
          ......
}

addView

/frameworks/base/core/java/android/view/WindowManagerImpl.java

    @Override
    public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
        applyDefaultToken(params);
        mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
    }

addView

/frameworks/base/core/java/android/view/WindowManagerGlobal.java

    public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
            ......

            root = new ViewRootImpl(view.getContext(), display);
            ......
            root.setView(view, wparams, panelParentView);
            ......
    }

setView

/frameworks/base/core/java/android/view/ViewRootImpl.java
创建mInputChannel，并传递给WMS

    /**
     * We have one child
     */
    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();
               }
               res = mWindowSession.addToDisplay(mWindow, mSeq,mWindowAttributes,getHostVisibility(), mDisplay.getDisplayId(), mTmpFrame,mAttachInfo.mContentInsets,
               mAttachInfo.mStableInsets,mAttachInfo.mOutsets,
               mAttachInfo.mDisplayCutout, mInputChannel,
               mTempInsets);
         ......
    }

addToDisplay

/frameworks/base/services/core/java/com/android/server/wm/Session.java

      @Override
    public int addToDisplay(IWindow window, int seq, WindowManager.LayoutParams attrs,
              int viewVisibility, int displayId, Rect outFrame, Rect outContentInsets,
              Rect outStableInsets, Rect outOutsets,
              DisplayCutout.ParcelableWrapper outDisplayCutout, InputChannel outInputChannel,
              InsetsState outInsetsState) {
          return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId, outFrame,
                  outContentInsets, outStableInsets, outOutsets, outDisplayCutout, outInputChannel,
                  outInsetsState);
      }

addWindow

/frameworks/base/services/core/java/com/android/server/wm/WindowManagerService.java

public int addWindow(Session session, IWindow client, int seq,
            LayoutParams attrs, int viewVisibility, int displayId, Rect outFrame,
            Rect outContentInsets, Rect outStableInsets, Rect outOutsets,
            DisplayCutout.ParcelableWrapper outDisplayCutout, InputChannel outInputChannel,
            InsetsState outInsetsState) {
           ......
           final WindowState win = new WindowState(this, session, client, token, parentWindow,
                    appOp[0], seq, attrs, viewVisibility, session.mUid,
                    session.mCanAddInternalSystemWindow);
           final boolean openInputChannels = (outInputChannel != null
                    && (attrs.inputFeatures & INPUT_FEATURE_NO_INPUT_CHANNEL) == 0);
            if  (openInputChannels) {
                win.openInputChannel(outInputChannel);
            }
           ......
 }

win.openInputChannel

    void openInputChannel(InputChannel outInputChannel) {
        if (mInputChannel != null) {
            throw new IllegalStateException("Window already has an input channel.");
        }
        String name = getName();
        //创建InputChannelPair
        InputChannel[] inputChannels = InputChannel.openInputChannelPair(name);
        //服务端InputChannel
        mInputChannel = inputChannels[0];
        //客户端InputChannel
        mClientChannel = inputChannels[1];
        mInputWindowHandle.token = mClient.asBinder();
        if (outInputChannel != null) {
            //将客户端InputChannel发送回ViewRootImpl
            mClientChannel.transferTo(outInputChannel);
            mClientChannel.dispose();
            mClientChannel = null;
        } else {
            // If the window died visible, we setup a dummy input channel, so that taps
            // can still detected by input monitor channel, and we can relaunch the app.
            // Create dummy event receiver that simply reports all events as handled.
            mDeadWindowEventReceiver = new DeadWindowEventReceiver(mClientChannel);
        }
        //将服务端InputChannel注册到InputDispatcher
        mWmService.mInputManager.registerInputChannel(mInputChannel, mClient.asBinder());
    }

openInputChannelPair

    /**
     * Creates a new input channel pair.  One channel should be provided to the input
     * dispatcher and the other to the application's input queue.
     * @param name The descriptive (non-unique) name of the channel pair.
     * @return A pair of input channels.  The first channel is designated as the
     * server channel and should be used to publish input events.  The second channel
     * is designated as the client channel and should be used to consume input events.
     */
    public static InputChannel[] openInputChannelPair(String name) {
        if (name == null) {
            throw new IllegalArgumentException("name must not be null");
        }

        if (DEBUG) {
            Slog.d(TAG, "Opening input channel pair '" + name + "'");
        }
        return nativeOpenInputChannelPair(name);
    }

nativeOpenInputChannelPair

/frameworks/base/core/jni/android_view_InputChannel.cpp

static jobjectArray android_view_InputChannel_nativeOpenInputChannelPair(JNIEnv* env,
        jclass clazz, jstring nameObj) {
    ScopedUtfChars nameChars(env, nameObj);
    std::string name = nameChars.c_str();

    sp<InputChannel> serverChannel;
    sp<InputChannel> clientChannel;
    //创建Native层serverChannel和clientChannel
    status_t result = InputChannel::openInputChannelPair(name, serverChannel, clientChannel);
    .......
    //创建java层数组，用在后面存放java层InputChannel，并返回
    jobjectArray channelPair = env->NewObjectArray(2, gInputChannelClassInfo.clazz, NULL);
    ......
    //创建java层的server端的InputChannel对象
    jobject serverChannelObj = android_view_InputChannel_createInputChannel(env,
            std::make_unique<NativeInputChannel>(serverChannel));
    ......
    //创建java层的clien端的InputChannel对象
    jobject clientChannelObj = android_view_InputChannel_createInputChannel(env,
            std::make_unique<NativeInputChannel>(clientChannel));
    ......
    env->SetObjectArrayElement(channelPair, 0, serverChannelObj);
    env->SetObjectArrayElement(channelPair, 1, clientChannelObj);
    return channelPair;
}

InputChannel::openInputChannelPair

此方法中创建了一对NativeInputChannel和一对socket，在InputChannel构造函数中通过setFd将两个InputChanne和两个socket一一关联上,后去可以通过getFd拿到对于InputChannel的socket连接
/frameworks/native/libs/input/InputTransport.cpp

status_t InputChannel::openInputChannelPair(const std::string& name,
        sp<InputChannel>& outServerChannel, sp<InputChannel>& outClientChannel) {
    //一对socket数组
    int sockets[2];
    if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sockets)) {
        status_t result = -errno;
        ALOGE("channel '%s' ~ Could not create socket pair.  errno=%d",
                name.c_str(), errno);
        outServerChannel.clear();
        outClientChannel.clear();
        return result;
    }

    int bufferSize = SOCKET_BUFFER_SIZE;
    //对两个socker分别设置
    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));

    std::string serverChannelName = name;
    //创建ServerChannel，后缀名+server
    serverChannelName += " (server)";
    //通过setFd将sockets[0]和ServerChannel关联上
    outServerChannel = new InputChannel(serverChannelName, sockets[0]);

    std::string clientChannelName = name;
    //创建ClientChannel，后缀名+client
    clientChannelName += " (client)";
    //通过setFd将sockets[1]和ClientChannel关联上
    outClientChannel = new InputChannel(clientChannelName, sockets[1]);
    return OK;
}
InputChannel::InputChannel(const std::string& name, int fd) :
          mName(name) {
          ......
          setFd(fd);
  }

继续看nativeOpenInputChannelPair方法后半部分 android_view_InputChannel_createInputChannel

此方法会创建一个java数组，一对java层InputChannel,并将一对NativeInputChannel赋值给java层InputChannel的mPtr属性，并将server端InputChannel赋值给数组0，将client端InputChannel赋值给数组1,最后将数组返回给java层

//指向java层InputChannel的mPtr属性
gInputChannelClassInfo.mPtr = GetFieldIDOrDie(env, gInputChannelClassInfo.clazz, "mPtr", "J");
static jobjectArray android_view_InputChannel_nativeOpenInputChannelPair(JNIEnv* env,
        jclass clazz, jstring nameObj) {
   //创建一个java数组，大小为2,类型为InputChannel
   jobjectArray channelPair = env->NewObjectArray(2, gInputChannelClassInfo.clazz, NULL);
   ......
   //将server端的NativeInputChannel赋值给java层的server端的InputChannel
   jobject serverChannelObj = android_view_InputChannel_createInputChannel(env,
            std::make_unique<NativeInputChannel>(serverChannel));
    ......
    //将client端的NativeInputChannel赋值给java层的client端的InputChannel
    jobject clientChannelObj = android_view_InputChannel_createInputChannel(env,
            std::make_unique<NativeInputChannel>(clientChannel));
    ......
    static jobject android_view_InputChannel_createInputChannel(JNIEnv* env,
        std::unique_ptr<NativeInputChannel> nativeInputChannel) {
        //创建java层inputChannel对象
    jobject inputChannelObj = env->NewObject(gInputChannelClassInfo.clazz,
            gInputChannelClassInfo.ctor);
       //当inputChannel不为空
    if (inputChannelObj) {
        //给InputChannel的mPtr属性赋值为NativeInputChannel
        android_view_InputChannel_setNativeInputChannel(env, inputChannelObj,
                 nativeInputChannel.release());
    }
    return inputChannelObj;
}
static void android_view_InputChannel_setNativeInputChannel(JNIEnv* env, jobject inputChannelObj,
        NativeInputChannel* nativeInputChannel) {
    //jni方法，给inputChannelObj对象的gInputChannelClassInfo.mPtr属性赋值为reinterpret_cast<jlong>(nativeInputChannel)
    env->SetLongField(inputChannelObj, gInputChannelClassInfo.mPtr,
             reinterpret_cast<jlong>(nativeInputChannel));
}
    //将server端InputChannel赋值给数组0的位置
    env->SetObjectArrayElement(channelPair, 0, serverChannelObj);
    //将client端InputChannel赋值给数组0的位置
    env->SetObjectArrayElement(channelPair, 1, clientChannelObj);
    //将InputChannel数组返回给java层
    return channelPair;
    }

回到WindowState

通过openInputChannelPair方法已经获取得到了InputChannel数组，并且数组0的位置是server端的InputChannel，数组1的位置是client端的InputChannel

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/frameworks/base/services/core/java/com/android/server/wm/WindowState.java

    void openInputChannel(InputChannel outInputChannel) {
        if (mInputChannel != null) {
            throw new IllegalStateException("Window already has an input channel.");
        }
        String name = getName();
        //native层返回的InputChannel数组，server端和cilent端
        InputChannel[] inputChannels = InputChannel.openInputChannelPair(name);
        //server端InputChannel
        mInputChannel = inputChannels[0];
        //client端InputChannel
        mClientChannel = inputChannels[1];
        mInputWindowHandle.token = mClient.asBinder();
        if (outInputChannel != null) {
            //将client端InputChannel传回到ViewRootImpl
            mClientChannel.transferTo(outInputChannel);
            mClientChannel.dispose();
            mClientChannel = null;
        } else {
            // If the window died visible, we setup a dummy input channel, so that taps
            // can still detected by input monitor channel, and we can relaunch the app.
            // Create dummy event receiver that simply reports all events as handled.
            mDeadWindowEventReceiver = new DeadWindowEventReceiver(mClientChannel);
        }
        //server端InputChannel注册到native层InputDispatcher
        mWmService.mInputManager.registerInputChannel(mInputChannel, mClient.asBinder());
    }

//将client端InputChannel传回到ViewRootImpl transferTo

/frameworks/base/core/java/android/view/InputChannel.java

    /**
     * Transfers ownership of the internal state of the input channel to another
     * instance and invalidates this instance.  This is used to pass an input channel
     * as an out parameter in a binder call.
     * @param other The other input channel instance.
     */
    public void transferTo(InputChannel outParameter) {
        if (outParameter == null) {
            throw new IllegalArgumentException("outParameter must not be null");
        }

        nativeTransferTo(outParameter);
    }

android_view_InputChannel_nativeTransferTo

/frameworks/base/core/jni/android_view_InputChannel.cpp

/*
mClientChannel.transferTo(outInputChannel);
*/
//注意该方法参数中的otherObj和obj，otherObj代表传递下来的参数outInputChannel，obj代表调用此方法的对象mClientChannel
static void android_view_InputChannel_nativeTransferTo(JNIEnv* env, jobject obj,
        jobject otherObj) {
        //当java层的outInputChannel的mPtr已经指向了一个NativeInputChannel时抛一个异常返回
    if (android_view_InputChannel_getNativeInputChannel(env, otherObj) != NULL) {
        jniThrowException(env, "java/lang/IllegalStateException",
                "Other object already has a native input channel.");
        return;
    }
    //获取java层mClientChannel的mPtr属性，mPtr属性会指向一个NativeInputChannel对象，根据前面分析此时mClientChannel的mPtr指向client端的NativeInputChannel
    NativeInputChannel* nativeInputChannel =
            android_view_InputChannel_getNativeInputChannel(env, obj);
    android_view_InputChannel_setNativeInputChannel(env, otherObj, nativeInputChannel);
    android_view_InputChannel_setNativeInputChannel(env, obj, NULL);
}
static NativeInputChannel* android_view_InputChannel_getNativeInputChannel(JNIEnv* env,
        jobject inputChannelObj) {
    //jni方法，获取inputChannelObj对象的gInputChannelClassInfo.mPtr属性
    jlong longPtr = env->GetLongField(inputChannelObj, gInputChannelClassInfo.mPtr);
    return reinterpret_cast<NativeInputChannel*>(longPtr);
}
static void android_view_InputChannel_setNativeInputChannel(JNIEnv* env, jobject inputChannelObj,
        NativeInputChannel* nativeInputChannel) {
        //jni方法，将inputChannelObj的gInputChannelClassInfo.mPtr属性赋值为nativeInputChannel
    env->SetLongField(inputChannelObj, gInputChannelClassInfo.mPtr,
             reinterpret_cast<jlong>(nativeInputChannel));
}

总结：上面的方法主要作用就是将mClientChannel的mPtr属性赋值给outInputChannel，并将mClientChannel的mPtr赋值为NULL，这样就实现了将mClientChannel与outInputChannel互换，outInputChannel是ViewRootImpl的传递过来的mInputChannel，达到了将mClientChannel传递个应用客户端的目的。

继续回到WindowState

/frameworks/base/services/core/java/com/android/server/wm/WindowState.java

    void openInputChannel(InputChannel outInputChannel) {
        if (mInputChannel != null) {
            throw new IllegalStateException("Window already has an input channel.");
        }
        String name = getName();
        //native层返回的InputChannel数组，server端和cilent端
        InputChannel[] inputChannels = InputChannel.openInputChannelPair(name);
        //server端InputChannel
        mInputChannel = inputChannels[0];
        //client端InputChannel
        mClientChannel = inputChannels[1];
        mInputWindowHandle.token = mClient.asBinder();
        if (outInputChannel != null) {
            //将client端InputChannel传回到ViewRootImpl
            mClientChannel.transferTo(outInputChannel);
            mClientChannel.dispose();
            mClientChannel = null;
        } else {
            // If the window died visible, we setup a dummy input channel, so that taps
            // can still detected by input monitor channel, and we can relaunch the app.
            // Create dummy event receiver that simply reports all events as handled.
            mDeadWindowEventReceiver = new DeadWindowEventReceiver(mClientChannel);
        }
        //server端InputChannel注册到native层InputDispatcher
        mWmService.mInputManager.registerInputChannel(mInputChannel, mClient.asBinder());
    }

client端的InputChannel已经传递回了ViewRootImpl，接着看server端的InputChannel如何注册到InputDispatcher的
//server端InputChannel注册到native层InputDispatcher
mWmService.mInputManager.registerInputChannel(mInputChannel, mClient.asBinder());

registerInputChannel

/frameworks/base/services/core/java/com/android/server/input/InputManagerService.java

    /**
     * Registers an input channel so that it can be used as an input event target.
     * @param inputChannel The input channel to register.
     * @param inputWindowHandle The handle of the input window associated with the
     * input channel, or null if none.
     */
    public void registerInputChannel(InputChannel inputChannel, IBinder token) {
        if (inputChannel == null) {
            throw new IllegalArgumentException("inputChannel must not be null.");
        }
        if (token == null) {
            token = new Binder();
        }
        inputChannel.setToken(token);
        //native方法
        nativeRegisterInputChannel(mPtr, inputChannel, Display.INVALID_DISPLAY);
    }

nativeRegisterInputChannel

/frameworks/base/services/core/jni/com_android_server_input_InputManagerService.cpp

static void nativeRegisterInputChannel(JNIEnv* env, jclass /* clazz */,
        jlong ptr, jobject inputChannelObj, jint displayId) {
    //ptr是java层InputManagerService中的mPtr属性，在InputManagerService初始化时指向了NativeInputManager
    NativeInputManager* im = reinterpret_cast<NativeInputManager*>(ptr);
    //通过java层传下来的inputChannels[0]获取到Native层的server端InputChannel
    sp<InputChannel> inputChannel = android_view_InputChannel_getInputChannel(env,
            inputChannelObj);
    if (inputChannel == nullptr) {
        throwInputChannelNotInitialized(env);
        return;
    }
    //注册inputChannel
    status_t status = im->registerInputChannel(env, inputChannel, displayId);
    if (status) {
        std::string message;
        message += StringPrintf("Failed to register input channel.  status=%d", status);
        jniThrowRuntimeException(env, message.c_str());
        return;
    }
    //设置handleInputChannelDisposed回调
    android_view_InputChannel_setDisposeCallback(env, inputChannelObj,
            handleInputChannelDisposed, im);
 }

android_view_InputChannel_getInputChannel

/frameworks/base/core/jni/android_view_InputChannel.cpp

sp<InputChannel> android_view_InputChannel_getInputChannel(JNIEnv* env, jobject inputChannelObj) {
    NativeInputChannel* nativeInputChannel =
            android_view_InputChannel_getNativeInputChannel(env, inputChannelObj);
    //inline sp<InputChannel> getInputChannel() { return mInputChannel; },返回server端的Nativa层的InputChannel
    return nativeInputChannel != NULL ? nativeInputChannel->getInputChannel() : NULL;
}

注册inputChannel，registerInputChannel

/frameworks/base/services/core/jni/com_android_server_input_InputManagerService.cpp

status_t NativeInputManager::registerInputChannel(JNIEnv* /* env */,
        const sp<InputChannel>& inputChannel, int32_t displayId) {
    ATRACE_CALL();
    return mInputManager->getDispatcher()->registerInputChannel(
            inputChannel, displayId);
}

registerInputChannel

调到InputDispatcher的registerInputChannel方法，
1.此方法会创建Connection，将server端InputChannel作为参数传进去，
2.获取之前InputChannel的Fd即socket[0]，将fd和connection关联，后续InputDispatch通过fd可以获取对应connection，通过connection获取server InputChannel和client InputChannel通信从而将事件分发到对应的应用窗口
3.将fd添加到Looper线程进行监听

//InputDispatcher.h
// All registered connections mapped by channel file descriptor.
KeyedVector<int, sp<Connection> > mConnectionsByFd GUARDED_BY(mLock);
status_t InputDispatcher::registerInputChannel(const sp<InputChannel>& inputChannel,
        int32_t displayId) {
    { // acquire lock
        ......
        //创建Connection对象
        sp<Connection> connection = new Connection(inputChannel, false /*monitor*/);
        //获取之前通过setFd存入的socket[0]
        int fd = inputChannel->getFd();
        //将fd和connection关联,后续InputDispatch通过fd可以获取对应connection，通过connection获取server InputChannel和client InputChannel通信从而将事件分发到对应的应用窗口
        mConnectionsByFd.add(fd, connection);
        mInputChannelsByToken[inputChannel->getToken()] = inputChannel;
        //将fd添加到Looper线程进行监听，在收到对端相应事件之后回调handleReceiveCallback
        mLooper->addFd(fd, 0, ALOOPER_EVENT_INPUT, handleReceiveCallback, this);
    } // release lock
    // Wake the looper because some connections have changed.
    mLooper->wake();
    return OK;
}

在创建Connection时将server端的inputChannel同步传给InputPublisher的mChannel
/frameworks/native/services/inputflinger/InputDispatcher.cpp

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

/frameworks/native/libs/input/InputTransport.cpp

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

好了，从java层传下来的inputChannels[0]就已经注册到了InputDispatcher并且将对应的Fd添加到了InputDispatcher的Loop进行监听，并且传进去了一个回调handleReceiveCallback，应用端窗口处理完输入事件之后回调此方法

接着需要看inputChannels[1]的Fd是如何添加到应用端进行监听的

回到ViewRootImpl

在上面流程addToDisplay方法执行完之后ViewRootImpl中的mInputChannel已经变成了client端的InputChannel即inputChannels[1]
/frameworks/base/core/java/android/view/ViewRootImpl.java

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
      ......
      mInputChannel = new InputChannel();
      res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                            getHostVisibility(), mDisplay.getDisplayId(), mTmpFrame,
                            mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
                            mAttachInfo.mOutsets, mAttachInfo.mDisplayCutout, mInputChannel,
                            mTempInsets);
                            ......
        if (mInputChannel != null) {
                    if (mInputQueueCallback != null) {
                        mInputQueue = new InputQueue();
                        mInputQueueCallback.onInputQueueCreated(mInputQueue);
                    }
                    mInputEventReceiver = new WindowInputEventReceiver(mInputChannel,
                            Looper.myLooper());
                }       
      ......
}

看WindowInputEventReceiver的创建

    final class WindowInputEventReceiver extends InputEventReceiver {
        public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {
            //client端InputChannel，UI线程的looper
            super(inputChannel, looper);
        }

调父类InputEventReceiver构造函数

    /**
     * Creates an input event receiver bound to the specified input channel.
     *
     * @param inputChannel The input channel.
     * @param looper The looper to use when invoking callbacks.
     */
    public InputEventReceiver(InputChannel inputChannel, Looper looper) {
        if (inputChannel == null) {
            throw new IllegalArgumentException("inputChannel must not be null");
        }
        if (looper == null) {
            throw new IllegalArgumentException("looper must not be null");
        }
        mInputChannel = inputChannel;
        //UI线程的messagequeue
        mMessageQueue = looper.getQueue();
        //native方法，将自己，client端的InputChannel和UI线程的messagequeue传进去
        mReceiverPtr = nativeInit(new WeakReference<InputEventReceiver>(this),
                inputChannel, mMessageQueue);

        mCloseGuard.open("dispose");
    }

nativeInit

/frameworks/base/core/jni/android_view_InputEventReceiver.cpp

static jlong nativeInit(JNIEnv* env, jclass clazz, jobject receiverWeak,
        jobject inputChannelObj, jobject messageQueueObj) {
    //见过很多次了该方法，通过传下来的cilent端的InputChannel获取对应的native层InputChannel
    sp<InputChannel> inputChannel = android_view_InputChannel_getInputChannel(env,
            inputChannelObj);
    if (inputChannel == NULL) {
        jniThrowRuntimeException(env, "InputChannel is not initialized.");
        return 0;
    }
    //通过传下来的messagequeue获取对于native层的messagequeue
    sp<MessageQueue> messageQueue = android_os_MessageQueue_getMessageQueue(env, messageQueueObj);
    if (messageQueue == NULL) {
        jniThrowRuntimeException(env, "MessageQueue is not initialized.");
        return 0;
    }
    //创建NativeInputEventReceiver
    sp<NativeInputEventReceiver> receiver = new NativeInputEventReceiver(env,
            receiverWeak, inputChannel, messageQueue);
    status_t status = receiver->initialize();
    if (status) {
        String8 message;
        message.appendFormat("Failed to initialize input event receiver.  status=%d", status);
        jniThrowRuntimeException(env, message.string());
        return 0;
    }
    receiver->incStrong(gInputEventReceiverClassInfo.clazz); // retain a reference for the object
    return reinterpret_cast<jlong>(receiver.get());
}

创建NativeInputEventReceiver

/frameworks/base/core/jni/android_view_InputEventReceiver.cpp

//给NativeInputEventReceiver成员变量赋值
NativeInputEventReceiver::NativeInputEventReceiver(JNIEnv* env,
        jobject receiverWeak, const sp<InputChannel>& inputChannel,
        const sp<MessageQueue>& messageQueue) :
        mReceiverWeakGlobal(env->NewGlobalRef(receiverWeak)),
        mInputConsumer(inputChannel), mMessageQueue(messageQueue),
        mBatchedInputEventPending(false), mFdEvents(0) {
    }
}

initialize

/frameworks/base/core/jni/android_view_InputEventReceiver.cpp

status_t NativeInputEventReceiver::initialize() {
    setFdEvents(ALOOPER_EVENT_INPUT);
    return OK;
}
void NativeInputEventReceiver::setFdEvents(int events) {
    if (mFdEvents != events) {
        mFdEvents = events;
        //获取client端InputChannel的Fd即socket[1]
        int fd = mInputConsumer.getChannel()->getFd();
        if (events) {
            //将fd添加到UI线程进行监听,回调传的this
            mMessageQueue->getLooper()->addFd(fd, 0, events, this, NULL);
        } else {
            mMessageQueue->getLooper()->removeFd(fd);
        }
    }
}

到此client端的Fd也已经传递到了UI线程进行监听，InputDispatch与ViewRootImpl的socket连接已经建立

总结：

当应用窗口添加到WMS会创建一个WindowState描述此窗口，接着创建一对java层InputChannel对应创建一对socket，对应创建一对native层InputChannel，还有一个server端的connection，connection，inputChannel，socket创建完成后通道就已经建立，InputDispatcher就可以将事件发送给对应窗口了
它们的联系如下:
server端：
1.java层的server端InputChannel的mPtr属性指向native层的server端InputChannel
2.native层的server端InputChannel创建时会创建server端socket，并在自己的构造方法中通过setFd将此socket存在mFd变量
3.将server端InputChannel向InputDispatch注册时会创建一个connection对象，并通过getFd方法获取到socket，以fd为key，connection为值放入一个类似map的数据结构mConnectionsByFd

client端和server一样只是少了创建connection