相关文章链接：
1. Android Framework - 学习启动篇
2. Android FrameWork - 开机启动 SystemServer 进程
相关源码文件：
/frameworks/base/services/java/com/android/server/SystemServer.java
/frameworks/base/services/core/java/com/android/server/input/InputManagerService.java
/frameworks/base/services/core/jni/com_android_server_input_InputManagerService.cpp
/frameworks/native/services/inputflinger/InputDispatcher.cpp
/frameworks/native/services/inputflinger/InputReader.cpp
/frameworks/native/services/inputflinger/InputManager.cpp
/frameworks/native/services/inputflinger/EventHub.cpp
1. 梳理概述
对于 Android 上层事件分发的过程，大家应该都是比较熟悉的，因为这是自定义 View 的一个知识点，也是前几年面试常问的一个问题。但只是知道上层的事件分发过程可能还不够，因为很多高级功能开发需要依赖底层的一些知识。我们应该都知道事件一般会传递到 activity 根布局 view 的 dispatchTouchEvent 方法，那么我们有没有思考过事件的源头在哪里？这个事件最初到底是从哪里发出来的？
这里我们先梳理做一个整体的总结，手机点击屏幕首先从硬件传递到驱动，我们之前提到过在 linux 内核系统中一切皆文件，因此我们只需要监听 /dev/input 驱动文件的变化就能读取到事件；所以在 Android 系统中会有一个 InputReader 专门来负责读取 Input 事件，还有一个 InputDispatcher 专门把读取到的 Input 事件分发出来。
2. IMS 的启动过程
/**
* Starts a miscellaneous grab bag of stuff that has yet to be refactored
* and organized.
*/
private void startOtherServices() {
final Context context = mSystemContext;
...
// 创建 InputManagerService
InputManagerService inputManager = new InputManagerService(context);
// 创建 WindowManagerService
wm = WindowManagerService.main(context, inputManager,
mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL,
!mFirstBoot, mOnlyCore);
// 注册系统服务
ServiceManager.addService(Context.WINDOW_SERVICE, wm);
ServiceManager.addService(Context.INPUT_SERVICE, inputManager);
// 设置管理的 callback
inputManager.setWindowManagerCallbacks(wm.getInputMonitor());
inputManager.start();
}
public InputManagerService(Context context) {
this.mContext = context;
// 创建 InputManagerHandler
this.mHandler = new InputManagerHandler(DisplayThread.get().getLooper());
...
// native 层初始化，这里会用到 handler 的 looper 的底层通信机制，handler 也是可以跨进程通信的
mPtr = nativeInit(this, mContext, mHandler.getLooper().getQueue());
}
static jlong nativeInit(JNIEnv* env, jclass /* clazz */,
jobject serviceObj, jobject contextObj, jobject messageQueueObj) {
// 拿到 native 层的 MessageQueue 对象
sp messageQueue = android_os_MessageQueue_getMessageQueue(env, messageQueueObj);
if (messageQueue == NULL) {
jniThrowRuntimeException(env, "MessageQueue is not initialized.");
return 0;
}
// 创建 native 层的 NativeInputManager
NativeInputManager* im = new NativeInputManager(contextObj, serviceObj,
messageQueue->getLooper());
return reinterpret_cast(im);
}
NativeInputManager::NativeInputManager(jobject contextObj,
jobject serviceObj, const sp& looper) :
mLooper(looper), mInteractive(true) {
...
// 创建 EventHub 与 InputManager
sp eventHub = new EventHub();
mInputManager = new InputManager(eventHub, this, this);
}
InputManager::InputManager(
const sp& eventHub,
const sp& readerPolicy,
const sp& dispatcherPolicy) {
// 创建 InputDispatcher 与 InputReader
mDispatcher = new InputDispatcher(dispatcherPolicy);
mReader = new InputReader(eventHub, readerPolicy, mDispatcher);
initialize();
}
void InputManager::initialize() {
// 创建 InputDispatcher 与 InputReader 线程
mReaderThread = new InputReaderThread(mReader);
mDispatcherThread = new InputDispatcherThread(mDispatcher);
}
status_t InputManager::start() {
// 分别启动 InputDispatcher 与 InputReader 线程
status_t result = mDispatcherThread->run("InputDispatcher", PRIORITY_URGENT_DISPLAY);
...
result = mReaderThread->run("InputReader", PRIORITY_URGENT_DISPLAY);
...
return OK;
}
IMS 的启动入口在 SystemServer 进程中，InputManagerService 在构建对象的时候会创建 native 层的 NativeInputManager 对象，NativeInputManager 中又会构建 EventHub 与 InputManager 对象，最后 InputManager 会分别创建和启动 InputDispatcher 与 InputReader 线程。
2. Input 事件读取
EventHub::EventHub(void) :
mBuiltInKeyboardId(NO_BUILT_IN_KEYBOARD), mNextDeviceId(1), mControllerNumbers(),
mOpeningDevices(0), mClosingDevices(0),
mNeedToSendFinishedDeviceScan(false),
mNeedToReopenDevices(false), mNeedToScanDevices(true),
mPendingEventCount(0), mPendingEventIndex(0), mPendingINotify(false) {
acquire_wake_lock(PARTIAL_WAKE_LOCK, WAKE_LOCK_ID);
// 创建 epoll
mEpollFd = epoll_create(EPOLL_SIZE_HINT);
mINotifyFd = inotify_init();
// 此处 DEVICE_PATH 为"/dev/input"，监听该设备路径，这个代码在驱动层，感兴趣大家自己跟一下
int result = inotify_add_watch(mINotifyFd, DEVICE_PATH, IN_DELETE | IN_CREATE);
struct epoll_event eventItem;
memset(&eventItem, 0, sizeof(eventItem));
eventItem.events = EPOLLIN;
eventItem.data.u32 = EPOLL_ID_INOTIFY;
// 添加 INotify 到 epoll 实例
result = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, mINotifyFd, &eventItem);
int wakeFds[2];
result = pipe(wakeFds); // 创建管道
mWakeReadPipeFd = wakeFds[0];
mWakeWritePipeFd = wakeFds[1];
// 将 pipe 的读和写都设置为非阻塞方式
result = fcntl(mWakeReadPipeFd, F_SETFL, O_NONBLOCK);
result = fcntl(mWakeWritePipeFd, F_SETFL, O_NONBLOCK);
eventItem.data.u32 = EPOLL_ID_WAKE;
// 添加管道的读端到 epoll 实例
result = epoll_ctl(mEpollFd, EPOLL_CTL_ADD, mWakeReadPipeFd, &eventItem);
...
}
InputReader::InputReader(const sp& eventHub,
const sp& policy,
const sp& listener) :
mContext(this), mEventHub(eventHub), mPolicy(policy),
mGlobalMetaState(0), mGeneration(1),
mDisableVirtualKeysTimeout(LLONG_MIN), mNextTimeout(LLONG_MAX),
mConfigurationChangesToRefresh(0) {
// 创建输入监听对象 QueuedInputListener 就是 InputDispatcher
mQueuedListener = new QueuedInputListener(listener);
...
}
void InputReader::loopOnce() {
int32_t oldGeneration;
int32_t timeoutMillis;
...
// 从 mEventHub 中获取 Events 事件 ，EVENT_BUFFER_SIZE = 256
size_t count = mEventHub->getEvents(timeoutMillis, mEventBuffer, EVENT_BUFFER_SIZE);
{ // acquire lock
AutoMutex _l(mLock);
mReaderIsAliveCondition.broadcast();
// 处理事件
if (count) {
processEventsLocked(mEventBuffer, count);
}
...
} // release lock
// 发送事件到 InputDispatcher
mQueuedListener->flush();
}
size_t EventHub::getEvents(int timeoutMillis, RawEvent* buffer, size_t bufferSize) {
struct input_event readBuffer[bufferSize];
// 原始事件
RawEvent* event = buffer;
// 容量大小
size_t capacity = bufferSize;
for (;;) {
nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
...
if (mNeedToScanDevices) {
mNeedToScanDevices = false;
// 扫描设备
scanDevicesLocked();
mNeedToSendFinishedDeviceScan = true;
}
// Grab the next input event.
bool deviceChanged = false;
while (mPendingEventIndex < mPendingEventCount) {
const struct epoll_event& eventItem = mPendingEventItems[mPendingEventIndex++];
// 从设备不断读取事件，放入到 readBuffer
// 获取 readBuffer 的数据, 将 input_event 信息, 封装成 RawEvent
}
// 等待input事件的到来
int pollResult = epoll_wait(mEpollFd, mPendingEventItems, EPOLL_MAX_EVENTS, timeoutMillis);
}
// 返回所读取的事件个数
return event - buffer;
}
void InputReader::processEventsLocked(const RawEvent* rawEvents, size_t count) {
for (const RawEvent* rawEvent = rawEvents; count;) {
int32_t type = rawEvent->type;
size_t batchSize = 1;
if (type < EventHubInterface::FIRST_SYNTHETIC_EVENT) {
int32_t deviceId = rawEvent->deviceId;
while (batchSize < count) {
if (rawEvent[batchSize].type >= EventHubInterface::FIRST_SYNTHETIC_EVENT
|| rawEvent[batchSize].deviceId != deviceId) {
break;
}
batchSize += 1;
}
// 真正分发事件
processEventsForDeviceLocked(deviceId, rawEvent, batchSize);
} else {
// 添加设备类型有：获取键盘源类型，键盘类设备类型， 鼠标类设备类型，触摸屏设备类型
switch (rawEvent->type) {
case EventHubInterface::DEVICE_ADDED:
addDeviceLocked(rawEvent->when, rawEvent->deviceId);
break;
...
}
}
count -= batchSize;
rawEvent += batchSize;
}
}
void InputReader::processEventsForDeviceLocked(int32_t deviceId,
const RawEvent* rawEvents, size_t count) {
// 这里主要分析触摸事件
ssize_t deviceIndex = mDevices.indexOfKey(deviceId);
InputDevice* device = mDevices.valueAt(deviceIndex);
device->process(rawEvents, count);
}
void TouchInputMapper::dispatchMotion(nsecs_t when, uint32_t policyFlags, uint32_t source,
int32_t action, int32_t actionButton, int32_t flags,
int32_t metaState, int32_t buttonState, int32_t edgeFlags,
const PointerProperties* properties, const PointerCoords* coords,
const uint32_t* idToIndex, BitSet32 idBits, int32_t changedId,
float xPrecision, float yPrecision, nsecs_t downTime) {
...
// 封装成 NotifyMotionArgs 通知给 InputDispatcher
NotifyMotionArgs args(when, getDeviceId(), source, policyFlags,
action, actionButton, flags, metaState, buttonState, edgeFlags,
mViewport.displayId, pointerCount, pointerProperties, pointerCoords,
xPrecision, yPrecision, downTime);
getListener()->notifyMotion(&args);
}
InputReader 线程启动后会不断的通过 EventHub 去读取事件信息，然后再把事件信息解析封装成不同的对象，最后再通过回掉的方式通知 InputDispatcher 。其中添加设备类型有：键盘类设备类型， 鼠标类设备类型，触摸屏设备类型等。
3. Input 事件分发
InputDispatcher::InputDispatcher(const sp& policy) :
mPolicy(policy),
mPendingEvent(NULL), mLastDropReason(DROP_REASON_NOT_DROPPED),
mAppSwitchSawKeyDown(false), mAppSwitchDueTime(LONG_LONG_MAX),
mNextUnblockedEvent(NULL),
mDispatchEnabled(false), mDispatchFrozen(false), mInputFilterEnabled(false),
mInputTargetWaitCause(INPUT_TARGET_WAIT_CAUSE_NONE) {
// 创建 Looper 对象
mLooper = new Looper(false);
// 获取分发超时参数
policy->getDispatcherConfiguration(&mConfig);
}
void InputDispatcher::dispatchOnce() {
nsecs_t nextWakeupTime = LONG_LONG_MAX;
{
AutoMutex _l(mLock);
// 唤醒等待线程，monitor() 用于监控 dispatcher 是否发生死锁
mDispatcherIsAliveCondition.broadcast();
if (!haveCommandsLocked()) {
// 当 mCommandQueue 不为空时处理
dispatchOnceInnerLocked(&nextWakeupTime);
}
if (runCommandsLockedInterruptible()) {
nextWakeupTime = LONG_LONG_MIN;
}
}
nsecs_t currentTime = now();
int timeoutMillis = toMillisecondTimeoutDelay(currentTime, nextWakeupTime);
// 进入等待，需要调用 mLooper.wake 方法来唤醒
mLooper->pollOnce(timeoutMillis);
}
void InputDispatcher::dispatchOnceInnerLocked(nsecs_t* nextWakeupTime) {
...
if (! mPendingEvent) {
if (mInboundQueue.isEmpty()) {
// Nothing to do if there is no pending event.
if (!mPendingEvent) {
// 没有事件需要处理直接返回
return;
}
} else {
// Inbound queue has at least one entry.
mPendingEvent = mInboundQueue.dequeueAtHead();
traceInboundQueueLengthLocked();
}
}
switch (mPendingEvent->type) {
...
case EventEntry::TYPE_KEY: {
...
// 分发 key 事件
done = dispatchKeyLocked(currentTime, typedEntry, &dropReason, nextWakeupTime);
break;
}
case EventEntry::TYPE_MOTION: {
// 分发触摸事件
done = dispatchMotionLocked(currentTime, typedEntry,
&dropReason, nextWakeupTime);
break;
}
}
...
}
bool InputDispatcher::dispatchMotionLocked(
nsecs_t currentTime, MotionEntry* entry, DropReason* dropReason, nsecs_t* nextWakeupTime) {
...
if (isPointerEvent) {
// Pointer event. (eg. touchscreen)
injectionResult = findTouchedWindowTargetsLocked(currentTime,
entry, inputTargets, nextWakeupTime, &conflictingPointerActions);
} else {
// Non touch event. (eg. trackball)
injectionResult = findFocusedWindowTargetsLocked(currentTime,
entry, inputTargets, nextWakeupTime);
}
if (injectionResult == INPUT_EVENT_INJECTION_PENDING) {
return false;
}
// 最后开始分发
dispatchEventLocked(currentTime, entry, inputTargets);
return true;
}
int32_t InputDispatcher::findTouchedWindowTargetsLocked(nsecs_t currentTime,
const MotionEntry* entry, Vector& inputTargets, nsecs_t* nextWakeupTime,
bool* outConflictingPointerActions) {
if (newGesture || (isSplit && maskedAction == AMOTION_EVENT_ACTION_POINTER_DOWN)) {
// 遍历所有的 mWindowHandles
size_t numWindows = mWindowHandles.size();
for (size_t i = 0; i < numWindows; i++) {
sp windowHandle = mWindowHandles.itemAt(i);
const InputWindowInfo* windowInfo = windowHandle->getInfo();
if (windowInfo->displayId != displayId) {
continue; // wrong display
}
int32_t flags = windowInfo->layoutParamsFlags;
if (windowInfo->visible) {
// 可见，并且 flags 属性不是 InputWindowInfo::FLAG_NOT_TOUCHABLE
if (! (flags & InputWindowInfo::FLAG_NOT_TOUCHABLE)) {
isTouchModal = (flags & (InputWindowInfo::FLAG_NOT_FOCUSABLE
| InputWindowInfo::FLAG_NOT_TOUCH_MODAL)) == 0;
// 点击的是不是当前 window 的覆盖
if (isTouchModal || windowInfo->touchableRegionContainsPoint(x, y)) {
// found touched window, exit window loop
// 找到了当前触摸的 window
newTouchedWindowHandle = windowHandle;
break;
}
}
}
}
mTempTouchState.addOrUpdateWindow(newTouchedWindowHandle, targetFlags, pointerIds);
} else {
...
}
// 再把 mTempTouchState 收集到的 windows 添加到 inputTargets 中
for (size_t i = 0; i < mTempTouchState.windows.size(); i++) {
const TouchedWindow& touchedWindow = mTempTouchState.windows.itemAt(i);
addWindowTargetLocked(touchedWindow.windowHandle, touchedWindow.targetFlags,
touchedWindow.pointerIds, inputTargets);
}
...
return injectionResult;
}
void InputDispatcher::dispatchEventLocked(nsecs_t currentTime,
EventEntry* eventEntry, const Vector& inputTargets) {
for (size_t i = 0; i < inputTargets.size(); i++) {
const InputTarget& inputTarget = inputTargets.itemAt(i);
// 根据 inputChannel 的 fd 从 mConnectionsByFd 队列中查询目标 connection.
ssize_t connectionIndex = getConnectionIndexLocked(inputTarget.inputChannel);
if (connectionIndex >= 0) {
// 找到目标连接
sp connection = mConnectionsByFd.valueAt(connectionIndex);
// 准备分发事件出去了
prepareDispatchCycleLocked(currentTime, connection, eventEntry, &inputTarget);
} else {
...
}
}
}
void InputDispatcher::enqueueDispatchEntriesLocked(nsecs_t currentTime,
const sp& connection, EventEntry* eventEntry, const InputTarget* inputTarget) {
bool wasEmpty = connection->outboundQueue.isEmpty();
// Enqueue dispatch entries for the requested modes.
enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,
InputTarget::FLAG_DISPATCH_AS_HOVER_EXIT);
enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,
InputTarget::FLAG_DISPATCH_AS_OUTSIDE);
enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,
InputTarget::FLAG_DISPATCH_AS_HOVER_ENTER);
enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,
InputTarget::FLAG_DISPATCH_AS_IS);
enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,
InputTarget::FLAG_DISPATCH_AS_SLIPPERY_EXIT);
enqueueDispatchEntryLocked(connection, eventEntry, inputTarget,
InputTarget::FLAG_DISPATCH_AS_SLIPPERY_ENTER);
// If the outbound queue was previously empty, start the dispatch cycle going.
if (wasEmpty && !connection->outboundQueue.isEmpty()) {
startDispatchCycleLocked(currentTime, connection);
}
}
void InputDispatcher::startDispatchCycleLocked(nsecs_t currentTime,
const sp& connection) {
while (connection->status == Connection::STATUS_NORMAL
&& !connection->outboundQueue.isEmpty()) {
...
switch (eventEntry->type) {
case EventEntry::TYPE_KEY: {
...
break;
}
case EventEntry::TYPE_MOTION: {
MotionEntry* motionEntry = static_cast(eventEntry);
...
// 通过 connection 的 inputPublisher 发布出去了
// Publish the motion event.
status = connection->inputPublisher.publishMotionEvent(dispatchEntry->seq,
motionEntry->deviceId, motionEntry->source,
dispatchEntry->resolvedAction, motionEntry->actionButton,
dispatchEntry->resolvedFlags, motionEntry->edgeFlags,
motionEntry->metaState, motionEntry->buttonState,
xOffset, yOffset, motionEntry->xPrecision, motionEntry->yPrecision,
motionEntry->downTime, motionEntry->eventTime,
motionEntry->pointerCount, motionEntry->pointerProperties,
usingCoords);
break;
}
...
}
}
InputDispatcher 采用的是 Looper 的唤醒与等待，这个跟之前分析 Handler 的底层原理是一样的。收到事件后首先会找到分发的目标窗口信息，然后通过 inputTarget 的 inputChannel 找到通信连接，最后再把事件通过 connection 发布出来，至于发到哪里去了？我们需要熟悉后面的 WindowManagerService 的源码。
视频地址：https://pan.baidu.com/s/1vY_Vb3AaIB9UUWJdPMLOQQ
视频密码：566q