IMS启动时会调用InputReader.start()方法

InputReader.cpp
status_t InputReader::start() {
    if (mThread) {
        return ALREADY_EXISTS;
    }
    mThread = std::make_unique<InputThread>(
            "InputReader", [this]() { loopOnce(); }, [this]() { mEventHub->wake(); });
    return OK;
}

当线程开始运行后，将会在内建的线程循环中不断地调用threadLoop（），直到此函数返回false，则退出线程循环，从而结束线程。

InputReader的一次线程循环的工作思路非常清晰，一共三步：

□首先从EventHub中抽取未处理的事件列表。这些事件分为两类，一类是从设备节点中读取的原始输入事件，另一类则是输入设备可用性变化事件，简称为设备事件。

□通过processEventsLocked（）对事件进行处理。对于设备事件，此函数对根据设备的可用性加载或移除设备对应的配置信息。对于原始输入事件，则在进行转译、封装与加工后将结果暂存到mQueuedListener中。

□所有事件处理完毕后，调用mQueuedListener.flush（）将所有暂存的输入事件一次性地交付给InputDispatcher。

void InputReader::loopOnce() {
    int32_t oldGeneration;
    int32_t timeoutMillis;
    // Copy some state so that we can access it outside the lock later.
    bool inputDevicesChanged = false;
    std::vector<InputDeviceInfo> inputDevices;
    std::list<NotifyArgs> notifyArgs;
    { // acquire lock
        std::scoped_lock _l(mLock);

        oldGeneration = mGeneration;
        timeoutMillis = -1;

        auto changes = mConfigurationChangesToRefresh;
        if (changes.any()) {
            mConfigurationChangesToRefresh.clear();
            timeoutMillis = 0;
            refreshConfigurationLocked(changes);
        } else if (mNextTimeout != LLONG_MAX) {
            nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
            timeoutMillis = toMillisecondTimeoutDelay(now, mNextTimeout);
        }
    } // release lock

    std::vector<RawEvent> events = mEventHub->getEvents(timeoutMillis);

    { // acquire lock
        std::scoped_lock _l(mLock);
        mReaderIsAliveCondition.notify_all();
// 如果有事件信息，调用processEventsLocked()函数对事件进行加工处理
        if (!events.empty()) {
            notifyArgs += processEventsLocked(events.data(), events.size());
        }

        if (mNextTimeout != LLONG_MAX) {
            nsecs_t now = systemTime(SYSTEM_TIME_MONOTONIC);
            if (now >= mNextTimeout) {
                if (debugRawEvents()) {
                    ALOGD("Timeout expired, latency=%0.3fms", (now - mNextTimeout) * 0.000001f);
                }
                mNextTimeout = LLONG_MAX;
                notifyArgs += timeoutExpiredLocked(now);
            }
        }

        if (oldGeneration != mGeneration) {
            inputDevicesChanged = true;
            inputDevices = getInputDevicesLocked();
            notifyArgs.emplace_back(
                    NotifyInputDevicesChangedArgs{mContext.getNextId(), inputDevices});
        }
    } // release lock

    // Send out a message that the describes the changed input devices.
    if (inputDevicesChanged) {
        mPolicy->notifyInputDevicesChanged(inputDevices);
    }

    // Notify the policy of the start of every new stylus gesture outside the lock.
    for (const auto& args : notifyArgs) {
        const auto* motionArgs = std::get_if<NotifyMotionArgs>(&args);
        if (motionArgs != nullptr && isStylusPointerGestureStart(*motionArgs)) {
            mPolicy->notifyStylusGestureStarted(motionArgs->deviceId, motionArgs->eventTime);
        }
    }

    notifyAll(std::move(notifyArgs));

    // Flush queued events out to the listener.
    // This must happen outside of the lock because the listener could potentially call
    // back into the InputReader's methods, such as getScanCodeState, or become blocked
    // on another thread similarly waiting to acquire the InputReader lock thereby
    // resulting in a deadlock.  This situation is actually quite plausible because the
    // listener is actually the input dispatcher, which calls into the window manager,
    // which occasionally calls into the input reader.
    mQueuedListener.flush();
}

processEventsLocked（）会分别处理原始输入事件与设备增删事件。

对于原始输入事件，由于EventHub会将属于同一输入设备的原始输入事件放在一起，因此processEventsLocked（）可以使processEventsForDeviceLocked（）同时处理来自同一输入设备的一批事件。

std::list<NotifyArgs> InputReader::processEventsLocked(const RawEvent* rawEvents, size_t count) {
    std::list<NotifyArgs> out;
    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;
            }
            if (debugRawEvents()) {
                ALOGD("BatchSize: %zu Count: %zu", batchSize, count);
            }
            out += processEventsForDeviceLocked(deviceId, rawEvent, batchSize);
        } else {
            switch (rawEvent->type) {
                case EventHubInterface::DEVICE_ADDED:
                    addDeviceLocked(rawEvent->when, rawEvent->deviceId);
                    break;
                case EventHubInterface::DEVICE_REMOVED:
                    removeDeviceLocked(rawEvent->when, rawEvent->deviceId);
                    break;
                case EventHubInterface::FINISHED_DEVICE_SCAN:
                    handleConfigurationChangedLocked(rawEvent->when);
                    break;
                default:
                    ALOG_ASSERT(false); // can't happen
                    break;
            }
        }
        count -= batchSize;
        rawEvent += batchSize;
    }
    return out;
}

std::list<NotifyArgs> InputReader::processEventsForDeviceLocked(int32_t eventHubId,
                                                                const RawEvent* rawEvents,
                                                                size_t count) {
    auto deviceIt = mDevices.find(eventHubId);
    if (deviceIt == mDevices.end()) {
        ALOGW("Discarding event for unknown eventHubId %d.", eventHubId);
        return {};
    }

    std::shared_ptr<InputDevice>& device = deviceIt->second;
    if (device->isIgnored()) {
        // ALOGD("Discarding event for ignored deviceId %d.", deviceId);
        return {};
    }

    return device->process(rawEvents, count);
}

InputDevice.cpp
std::list<NotifyArgs> InputDevice::process(const RawEvent* rawEvents, size_t count) {
    // Process all of the events in order for each mapper.
    // We cannot simply ask each mapper to process them in bulk because mappers may
    // have side-effects that must be interleaved.  For example, joystick movement events and
    // gamepad button presses are handled by different mappers but they should be dispatched
    // in the order received.
    std::list<NotifyArgs> out;
    for (const RawEvent* rawEvent = rawEvents; count != 0; rawEvent++) {
        if (debugRawEvents()) {
            const auto [type, code, value] =
                    InputEventLookup::getLinuxEvdevLabel(rawEvent->type, rawEvent->code,
                                                         rawEvent->value);
            ALOGD("Input event: eventHubDevice=%d type=%s code=%s value=%s when=%" PRId64,
                  rawEvent->deviceId, type.c_str(), code.c_str(), value.c_str(), rawEvent->when);
        }

        if (mDropUntilNextSync) {
            if (rawEvent->type == EV_SYN && rawEvent->code == SYN_REPORT) {
                mDropUntilNextSync = false;
                ALOGD_IF(debugRawEvents(), "Recovered from input event buffer overrun.");
            } else {
                ALOGD_IF(debugRawEvents(),
                         "Dropped input event while waiting for next input sync.");
            }
        } else if (rawEvent->type == EV_SYN && rawEvent->code == SYN_DROPPED) {
            ALOGI("Detected input event buffer overrun for device %s.", getName().c_str());
            mDropUntilNextSync = true;
            out += reset(rawEvent->when);
        } else {
            for_each_mapper_in_subdevice(rawEvent->deviceId, [&](InputMapper& mapper) {
                out += mapper.process(rawEvent);
            });
        }
        --count;
    }
    return out;
}

InputMapper是InputReader中实际进行原始输入事件加工的场所，它有一系列的子类，分别用于加工不同类型的原始输入事件。而InputDevice的process（）函数使用InputMapper的方式是一个简化了的职责链（chain of responsibility）设计模式。InputDevice不需要知道哪一个InputMapper可以处理一个原始输入事件，只须将一个事件逐个交给每一个InputMapper尝试处理，如果InputMapper可以接受这个事件则处理之，否则什么都不做。

根据设备的类型，将设备做如下分配

InputMapper的种类实在很多，对所有类型都进行详细分析并不现实。选择KeyboardInputMapper和MultiTouchInputMapper两个常用并且具有代表性的InputMapper进行探讨

键盘事件的处理

KeyboardInputMapper的process（）函数比较简单

□通过processKey（）按键事件做进一步处理。

mQueuedListener.flush();

根据扫描码获取虚拟键值以及功能值后，KeyboardInputMapper：：process（）调用了processKey（）函数对按键事件做进一步处理。

将键盘信息转化为NotifyKeyArgs，返回到loopOnce的loopOnce中，通知事件分发

触摸事件的处理

触摸事件的处理

std::list<NotifyArgs> MultiTouchInputMapper::process(const RawEvent* rawEvent) {
    std::list<NotifyArgs> out = TouchInputMapper::process(rawEvent);

    mMultiTouchMotionAccumulator.process(rawEvent);
    return out;
}

事件处理完成后回到最初的

mQueuedListener.flush(); // 将事件交给inputDispatcher的过程

 

InputDispatcher继承了InputDispatcherInterface接口
class InputDispatcher : public android::InputDispatcherInterface {

void InputListenerInterface::notify(const NotifyArgs& generalArgs) {
    Visitor v{
            [&](const NotifyInputDevicesChangedArgs& args) { notifyInputDevicesChanged(args); },
            [&](const NotifyConfigurationChangedArgs& args) { notifyConfigurationChanged(args); },
            [&](const NotifyKeyArgs& args) { notifyKey(args); },
            [&](const NotifyMotionArgs& args) { notifyMotion(args); },
            [&](const NotifySwitchArgs& args) { notifySwitch(args); },
            [&](const NotifySensorArgs& args) { notifySensor(args); },
            [&](const NotifyVibratorStateArgs& args) { notifyVibratorState(args); },
            [&](const NotifyDeviceResetArgs& args) { notifyDeviceReset(args); },
            [&](const NotifyPointerCaptureChangedArgs& args) { notifyPointerCaptureChanged(args); },
    };
    std::visit(v, generalArgs);
}

以motion事件为例

void InputDispatcher::notifyMotion(const NotifyMotionArgs& args) {
    if (debugInboundEventDetails()) {
        ALOGD("notifyMotion - id=%" PRIx32 " eventTime=%" PRId64 ", deviceId=%d, source=%s, "
              "displayId=%" PRId32 ", policyFlags=0x%x, "
              "action=%s, actionButton=0x%x, flags=0x%x, metaState=0x%x, buttonState=0x%x, "
              "edgeFlags=0x%x, xPrecision=%f, yPrecision=%f, xCursorPosition=%f, "
              "yCursorPosition=%f, downTime=%" PRId64,
              args.id, args.eventTime, args.deviceId, inputEventSourceToString(args.source).c_str(),
              args.displayId, args.policyFlags, MotionEvent::actionToString(args.action).c_str(),
              args.actionButton, args.flags, args.metaState, args.buttonState, args.edgeFlags,
              args.xPrecision, args.yPrecision, args.xCursorPosition, args.yCursorPosition,
              args.downTime);
        for (uint32_t i = 0; i < args.pointerCount; i++) {
            ALOGD("  Pointer %d: id=%d, toolType=%s, x=%f, y=%f, pressure=%f, size=%f, "
                  "touchMajor=%f, touchMinor=%f, toolMajor=%f, toolMinor=%f, orientation=%f",
                  i, args.pointerProperties[i].id,
                  ftl::enum_string(args.pointerProperties[i].toolType).c_str(),
                  args.pointerCoords[i].getAxisValue(AMOTION_EVENT_AXIS_X),
                  args.pointerCoords[i].getAxisValue(AMOTION_EVENT_AXIS_Y),
                  args.pointerCoords[i].getAxisValue(AMOTION_EVENT_AXIS_PRESSURE),
                  args.pointerCoords[i].getAxisValue(AMOTION_EVENT_AXIS_SIZE),
                  args.pointerCoords[i].getAxisValue(AMOTION_EVENT_AXIS_TOUCH_MAJOR),
                  args.pointerCoords[i].getAxisValue(AMOTION_EVENT_AXIS_TOUCH_MINOR),
                  args.pointerCoords[i].getAxisValue(AMOTION_EVENT_AXIS_TOOL_MAJOR),
                  args.pointerCoords[i].getAxisValue(AMOTION_EVENT_AXIS_TOOL_MINOR),
                  args.pointerCoords[i].getAxisValue(AMOTION_EVENT_AXIS_ORIENTATION));
        }
    }

    Result<void> motionCheck = validateMotionEvent(args.action, args.actionButton,
                                                   args.pointerCount, args.pointerProperties);
    if (!motionCheck.ok()) {
        LOG(ERROR) << "Invalid event: " << args.dump() << "; reason: " << motionCheck.error();
        return;
    }

    uint32_t policyFlags = args.policyFlags;
    policyFlags |= POLICY_FLAG_TRUSTED;

    android::base::Timer t;
    mPolicy.interceptMotionBeforeQueueing(args.displayId, args.eventTime, policyFlags);
    if (t.duration() > SLOW_INTERCEPTION_THRESHOLD) {
        ALOGW("Excessive delay in interceptMotionBeforeQueueing; took %s ms",
              std::to_string(t.duration().count()).c_str());
    }

    bool needWake = false;
    { // acquire lock
        mLock.lock();
        if (!(policyFlags & POLICY_FLAG_PASS_TO_USER)) {
            // Set the flag anyway if we already have an ongoing gesture. That would allow us to
            // complete the processing of the current stroke.
            const auto touchStateIt = mTouchStatesByDisplay.find(args.displayId);
            if (touchStateIt != mTouchStatesByDisplay.end()) {
                const TouchState& touchState = touchStateIt->second;
                if (touchState.deviceId == args.deviceId && touchState.isDown()) {
                    policyFlags |= POLICY_FLAG_PASS_TO_USER;
                }
            }
        }

        if (shouldSendMotionToInputFilterLocked(args)) {
            ui::Transform displayTransform;
            if (const auto it = mDisplayInfos.find(args.displayId); it != mDisplayInfos.end()) {
                displayTransform = it->second.transform;
            }

            mLock.unlock();

            MotionEvent event;
            event.initialize(args.id, args.deviceId, args.source, args.displayId, INVALID_HMAC,
                             args.action, args.actionButton, args.flags, args.edgeFlags,
                             args.metaState, args.buttonState, args.classification,
                             displayTransform, args.xPrecision, args.yPrecision,
                             args.xCursorPosition, args.yCursorPosition, displayTransform,
                             args.downTime, args.eventTime, args.pointerCount,
                             args.pointerProperties, args.pointerCoords);

            policyFlags |= POLICY_FLAG_FILTERED;
            if (!mPolicy.filterInputEvent(event, policyFlags)) {
                return; // event was consumed by the filter
            }

            mLock.lock();
        }

        // Just enqueue a new motion event.
        std::unique_ptr<MotionEntry> newEntry =
                std::make_unique<MotionEntry>(args.id, args.eventTime, args.deviceId, args.source,
                                              args.displayId, policyFlags, args.action,
                                              args.actionButton, args.flags, args.metaState,
                                              args.buttonState, args.classification, args.edgeFlags,
                                              args.xPrecision, args.yPrecision,
                                              args.xCursorPosition, args.yCursorPosition,
                                              args.downTime, args.pointerCount,
                                              args.pointerProperties, args.pointerCoords);

        if (args.id != android::os::IInputConstants::INVALID_INPUT_EVENT_ID &&
            IdGenerator::getSource(args.id) == IdGenerator::Source::INPUT_READER &&
            !mInputFilterEnabled) {
            const bool isDown = args.action == AMOTION_EVENT_ACTION_DOWN;
            mLatencyTracker.trackListener(args.id, isDown, args.eventTime, args.readTime);
        }

        needWake = enqueueInboundEventLocked(std::move(newEntry));
        mLock.unlock();
    } // release lock

    if (needWake) {
        mLooper->wake();
    }
}

到达InputDispatcher的Motion事件被保存在MotionEntry类中

bool InputDispatcher::enqueueInboundEventLocked(std::unique_ptr<EventEntry> newEntry) {
    bool needWake = mInboundQueue.empty();
    mInboundQueue.push_back(std::move(newEntry));
    EventEntry& entry = *(mInboundQueue.back());
    traceInboundQueueLengthLocked();

    switch (entry.type) {
        case EventEntry::Type::KEY: {
            LOG_ALWAYS_FATAL_IF((entry.policyFlags & POLICY_FLAG_TRUSTED) == 0,
                                "Unexpected untrusted event.");
            // Optimize app switch latency.
            // If the application takes too long to catch up then we drop all events preceding
            // the app switch key.
            const KeyEntry& keyEntry = static_cast<const KeyEntry&>(entry);
            if (isAppSwitchKeyEvent(keyEntry)) {
                if (keyEntry.action == AKEY_EVENT_ACTION_DOWN) {
                    mAppSwitchSawKeyDown = true;
                } else if (keyEntry.action == AKEY_EVENT_ACTION_UP) {
                    if (mAppSwitchSawKeyDown) {
                        if (DEBUG_APP_SWITCH) {
                            ALOGD("App switch is pending!");
                        }
                        mAppSwitchDueTime = keyEntry.eventTime + APP_SWITCH_TIMEOUT;
                        mAppSwitchSawKeyDown = false;
                        needWake = true;
                    }
                }
            }

            // If a new up event comes in, and the pending event with same key code has been asked
            // to try again later because of the policy. We have to reset the intercept key wake up
            // time for it may have been handled in the policy and could be dropped.
            if (keyEntry.action == AKEY_EVENT_ACTION_UP && mPendingEvent &&
                mPendingEvent->type == EventEntry::Type::KEY) {
                KeyEntry& pendingKey = static_cast<KeyEntry&>(*mPendingEvent);
                if (pendingKey.keyCode == keyEntry.keyCode &&
                    pendingKey.interceptKeyResult ==
                            KeyEntry::InterceptKeyResult::TRY_AGAIN_LATER) {
                    pendingKey.interceptKeyResult = KeyEntry::InterceptKeyResult::UNKNOWN;
                    pendingKey.interceptKeyWakeupTime = 0;
                    needWake = true;
                }
            }
            break;
        }

        case EventEntry::Type::MOTION: {
            LOG_ALWAYS_FATAL_IF((entry.policyFlags & POLICY_FLAG_TRUSTED) == 0,
                                "Unexpected untrusted event.");
            if (shouldPruneInboundQueueLocked(static_cast<MotionEntry&>(entry))) {
                mNextUnblockedEvent = mInboundQueue.back();
                needWake = true;
            }
            break;
        }
        case EventEntry::Type::FOCUS: {
            LOG_ALWAYS_FATAL("Focus events should be inserted using enqueueFocusEventLocked");
            break;
        }
        case EventEntry::Type::TOUCH_MODE_CHANGED:
        case EventEntry::Type::CONFIGURATION_CHANGED:
        case EventEntry::Type::DEVICE_RESET:
        case EventEntry::Type::SENSOR:
        case EventEntry::Type::POINTER_CAPTURE_CHANGED:
        case EventEntry::Type::DRAG: {
            // nothing to do
            break;
        }
    }

    return needWake;
}

通过这两个函数可以看出，到达InputDispatcher的Motion事件被保存在MotionEntry类中，然后排在mInboundQueue列表的队尾，这个mInboundQueue就是InputDispatcher的派发队列。MotionEntry是EventEntry的一个子类，保存了Motion事件的信息。Key事件也有一个KeyEntry与之对应。EventEntry是输入事件在InputDispatcher中的存在形式。另外，由于InputDispatcher在没有事件可以派发时（mInboundQueue为空），将会进入休眠状态，因此在将事件放入派发队列时，需要将派发线程唤醒。

上述过程运行在inputReader线程中，至此inputReader的处理完成