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Android开发No Focused Window ANR产生原理解析

2023-07-28 10:40:12 作者：尹学姐

这篇文章主要为大家介绍了Android开发No Focused Window ANR产生原理解析，有需要的朋友可以借鉴参考下，希望能够有所帮助，祝大家多多进步，早日升职加薪

引言

之前我们讲过因为事件没有得到及时处理，引起的ANR问题。但这只是Input Dispatching Timeout中的一种情况，还有一种情况，在我们应用中出现的也很常见，就是No Focused Window ANR，这个又是在哪些情况下产生的呢？

由之前的文章，我们知道，点击事件都是由InputDispatcher来分发的，我们直接来看InputDispatcher的源码。

No Focused Window ANR如何产生

如果是Key事件，或Motion事件，都需要找到焦点窗口取处理，都会调用到findFocusedWindowTargetsLocked()。

// frameworks/native/services/inputflinger/dispatcher/InputDispatcher.cpp
int32_t InputDispatcher::findFocusedWindowTargetsLocked(nsecs_t currentTime,
                                                        const EventEntry& entry,
                                                        std::vector<InputTarget>& inputTargets,
                                                        nsecs_t* nextWakeupTime) {
    std::string reason;
    int32_t displayId = getTargetDisplayId(entry);
    // mFocusedWindowHandlesByDisplay在setInputWindowsLocked()里赋值
    sp<InputWindowHandle> focusedWindowHandle =
            getValueByKey(mFocusedWindowHandlesByDisplay, displayId);
    // mFocusedApplicationHandlesByDisplay在setFocusedApplication()里赋值
    sp<InputApplicationHandle> focusedApplicationHandle =
            getValueByKey(mFocusedApplicationHandlesByDisplay, displayId);
    // focusedWindowHandle和focusedApplicationHandle都为空时表示当前无窗口，该事件会被丢弃，不会执行dispatchEventLocked
    // 一般出现两个都为空的场景，是在窗口切换的过程，此时不处理事件注入
    if (focusedWindowHandle == nullptr && focusedApplicationHandle == nullptr) {
        return INPUT_EVENT_INJECTION_FAILED;
    }
    // focusedWindowHandle为空但focusedApplicationHandle不为空时开始ANR检查
    if (focusedWindowHandle == nullptr && focusedApplicationHandle != nullptr) {
        // 默认mNoFocusedWindowTimeoutTime没有值，第一次检查ANR会走下面这个流程
        if (!mNoFocusedWindowTimeoutTime.has_value()) {
            // DEFAULT_INPUT_DISPATCHING_TIMEOUT = 5s * HwTimeoutMultiplier();
            // 默认input dispatch timeout时间时5s
            const nsecs_t timeout = focusedApplicationHandle->getDispatchingTimeout(
                    DEFAULT_INPUT_DISPATCHING_TIMEOUT.count());
            // 给mNoFocusedWindowTimeoutTime赋值，触发ANR时会检查这个值是否为空，不为空才触发ANR
            mNoFocusedWindowTimeoutTime = currentTime + timeout;
            // 把当前的focusedApplicationHandle赋值给mAwaitedFocusedApplication，触发ANR时会检查这个值是否为空，不为空才触发ANR
            mAwaitedFocusedApplication = focusedApplicationHandle;
            mAwaitedApplicationDisplayId = displayId;
            *nextWakeupTime = *mNoFocusedWindowTimeoutTime;
            // 返回INPUT_EVENT_INJECTION_PENDING表示dispatchKeyLocked()或者dispatchMotionLocked()为false
            return INPUT_EVENT_INJECTION_PENDING;
        } else if (currentTime > *mNoFocusedWindowTimeoutTime) {
            // Already raised ANR. Drop the event
            return INPUT_EVENT_INJECTION_FAILED;
        } else {
            // Still waiting for the focused window
            return INPUT_EVENT_INJECTION_PENDING;
        }
    }
    // 如果走到这个流程，说明没有ANR，清空mNoFocusedWindowTimeoutTime和mAwaitedFocusedApplication
    resetNoFocusedWindowTimeoutLocked();
    return INPUT_EVENT_INJECTION_SUCCEEDED;
}

主要逻辑：

如果focusedWindowHandle和focusedApplicationHandle都为null，一般发生在窗口切换的时候，返回INPUT_EVENT_INJECTION_FAILED，直接drop事件，不做处理
如果focusedWindowHandle为null，focusedApplicationHandle不为null，返回INPUT_EVENT_INJECTION_PENDING，在nextWakeupTime之后唤醒，检查是否发生ANR
- mNoFocusedWindowTimeoutTime：记录no focused window timeout的时间
- mAwaitedFocusedApplication：记录focusedApplicationHandle
- nextWakeupTime: 下次唤醒pollInner的时间

检查ANR逻辑

// frameworks/native/services/inputflinger/dispatcher/InputDispatcher.cpp
nsecs_t InputDispatcher::processAnrsLocked() {
    const nsecs_t currentTime = now();
    nsecs_t nextAnrCheck = LONG_LONG_MAX;
    // 在findFocusedWindowTargetsLocked()中，如果focusedWindowHandle为空，focusedApplicationHandle不为空，以下条件就会满足
    if (mNoFocusedWindowTimeoutTime.has_value() && mAwaitedFocusedApplication != nullptr) {
        // mNoFocusedWindowTimeoutTime为检查时间+5s，如果currentTime大于等于mNoFocusedWindowTimeoutTime，表示超时
        if (currentTime >= *mNoFocusedWindowTimeoutTime) {
            // 触发ANR流程，此处触发的ANR类型是xxx does not have a focused window
            processNoFocusedWindowAnrLocked();
            // 清空mAwaitedFocusedApplication，下次就不会再走ANR流程
            mAwaitedFocusedApplication.clear();
            mNoFocusedWindowTimeoutTime = std::nullopt;
            return LONG_LONG_MIN;
        } else {
            // Keep waiting
            const nsecs_t millisRemaining = ns2ms(*mNoFocusedWindowTimeoutTime - currentTime);
            ALOGW("Still no focused window. Will drop the event in %" PRId64 "ms", millisRemaining);
            // 还没有超时，更新检查时间
            nextAnrCheck = *mNoFocusedWindowTimeoutTime;
        }
    }
    ....
    // 如果走到这个流程，ANR类型是xxx is not responding. Waited xxx ms for xxx
    // 这个地方，focusedWindowHandle和focusedApplicationHandle都是不为空的场景
    onAnrLocked(*connection);
    return LONG_LONG_MIN;
}

主要流程:

如果mNoFocusedWindowTimeoutTime有值，且mAwaitedFocusedApplication不为空
- 超时：调用processNoFocusedWindowAnrLocked触发ANR
- 未超时：更新检查时间
继续检查input事件是否超时，如果超时，则调用onAnrLocked触发ANR

processNoFocusedAnrLocked的流程

// frameworks/native/services/inputflinger/dispatcher/InputDispatcher.cpp
void InputDispatcher::processNoFocusedWindowAnrLocked() {
    // 在触发ANR前，再获取一次当前的focusedApplication
    sp<InputApplicationHandle> focusedApplication =
            getValueByKey(mFocusedApplicationHandlesByDisplay, mAwaitedApplicationDisplayId);
    // 检查触发ANR时的条件是focusedApplication不为空
    // 如果此时focusedApplication为空，或者focusedApplication不等于前一个mAwaitedFocusedApplication表示已经切换application focus，取消触发ANR
    if (focusedApplication == nullptr ||
        focusedApplication->getApplicationToken() !=
                mAwaitedFocusedApplication->getApplicationToken()) {
        return; // The focused application has changed.
    }
    // 在触发ANR前，再获取一次当前的focusedWindowHandle 
    const sp<InputWindowHandle>& focusedWindowHandle =
            getFocusedWindowHandleLocked(mAwaitedApplicationDisplayId);
    // 检查触发ANR时focusedWindowHandle为空，如果此时focusedWindowHandle不为空，取消触发ANR
    if (focusedWindowHandle != nullptr) {
        return; // We now have a focused window. No need for ANR.
    }
    // 通过前面的判断，还是无法拦截，说明该ANR无可避免，最终触发ANR
    // 早期代码没有前面一系列的判断，是直接触发的ANR，会在性能较差的场景下出现误判
    onAnrLocked(mAwaitedFocusedApplication);
}

主要流程：

在这个方法里面，再次检查focusedApplication
- 如果当前focusedApplication为空，或者和之前记录的mAwaitedFocusedApplication不一致，则说明窗口已经切换，不需要报ANR
再次检查focusedWindow是否未空
- 如果不为空，则不需要报ANR
检查都通过之后，才会调用onAnrLocked，报no Focused Window ANR

focusedApplication设置流程

// frameworks/base/services/core/jni/com_android_server_input_InputManagerService.cpp
void InputDispatcher::setFocusedApplication(
        int32_t displayId, const sp<InputApplicationHandle>& inputApplicationHandle) {
    { // acquire lock
        std::scoped_lock _l(mLock);
        // 获取当前的focusedApplicationHandle
        sp<InputApplicationHandle> oldFocusedApplicationHandle =
                getValueByKey(mFocusedApplicationHandlesByDisplay, displayId);
        // 如果当前的focusedApplicationHandle跟触发ANR是的focusedApplicationHandle是一样且
        // 新的focusedApplicationHandle跟旧的不一样，说明focusedApplicationHandle有更新
        // 需要重置ANR计时
        if (oldFocusedApplicationHandle == mAwaitedFocusedApplication &&
            inputApplicationHandle != oldFocusedApplicationHandle) {
            // 重置ANR计时
            resetNoFocusedWindowTimeoutLocked();
        }
        if (inputApplicationHandle != nullptr && inputApplicationHandle->updateInfo()) {
            if (oldFocusedApplicationHandle != inputApplicationHandle) {
                // 赋值新的inputApplicationHandle到mFocusedApplicationHandlesByDisplay，在findFocusedWindowTargetsLocked()时用到
                mFocusedApplicationHandlesByDisplay[displayId] = inputApplicationHandle;
            }
        } else if (oldFocusedApplicationHandle != nullptr) {
            // 如果inputApplicationHandle为空，oldFocusedApplicationHandle不为空，需要清除oldFocusedApplicationHandle
            oldFocusedApplicationHandle.clear();
            // 走到这个流程会出现findFocusedWindowTargetsLocked()中focusedApplicationHandle为空
            mFocusedApplicationHandlesByDisplay.erase(displayId);
        }
    } // release lock
    // Wake up poll loop since it may need to make new input dispatching choices.
    mLooper->wake();
}

主要流程：

如果inputApplicationHandle与oldFocusedApplication，则要重置ANR计时
如果inputApplicationHandle不为空，则更新map中的值
如果inputApplicationHandle为空，则清除oldFocusedApplication

这个方法，是从AMS调过来的，主要流程如下图：

focusedWindow设置流程

// frameworks/native/services/inputflinger/dispatcher/InputDispatcher.cpp
// 当VSYNC信号来了之后，会调用到SurfaceFlinger的onMessageInvalidate()方法
// SurfaceFlinger::onMessageInvalidate() 
//   ==> SurfaceFlinger: updateInputFlinger()
//    ==> SurfaceFlinger: updateInputWindowInfo()
//      ==> InputManager::setInputWindows()
//        ==> InputDispatcher::setInputWindows()
//          ==> InputDispatcher::setInputWindowsLocked()
void InputDispatcher::setInputWindowsLocked(
        const std::vector<sp<InputWindowHandle>>& inputWindowHandles, int32_t displayId) {
    // ......
    const std::vector<sp<InputWindowHandle>> oldWindowHandles = getWindowHandlesLocked(displayId);
    // 更新mWindowHandlesByDisplay这个map，然后通过getWindowHandlesLocked()找newFocusedWindowHandle
    updateWindowHandlesForDisplayLocked(inputWindowHandles, displayId);
    sp<InputWindowHandle> newFocusedWindowHandle = nullptr;
    bool foundHoveredWindow = false;
    // 在mWindowHandlesByDisplay这个map里面找newFocusedWindowHandle
    for (const sp<InputWindowHandle>& windowHandle : getWindowHandlesLocked(displayId)) {
        // newFocusedWindowHandle要不为空，windowHandle具备focusable和visible属性
        if (!newFocusedWindowHandle && windowHandle->getInfo()->hasFocus &&
            windowHandle->getInfo()->visible) {
            // 给newFocusedWindowHandle赋值，最后这个值存到mFocusedWindowHandlesByDisplay这个map
            newFocusedWindowHandle = windowHandle;
        }
        if (windowHandle == mLastHoverWindowHandle) {
            foundHoveredWindow = true;
        }
    }
    if (!foundHoveredWindow) {
        mLastHoverWindowHandle = nullptr;
    }
    // 在mFocusedWindowHandlesByDisplay这个map里找当前的焦点窗口
    sp<InputWindowHandle> oldFocusedWindowHandle =
            getValueByKey(mFocusedWindowHandlesByDisplay, displayId);
    // 判断oldFocusedWindowHandle是否等于newFocusedWindowHandle，如果相等则不走focus change流程
    if (!haveSameToken(oldFocusedWindowHandle, newFocusedWindowHandle)) {
        // 如果当前的焦点窗口不为空，需要从mFocusedWindowHandlesByDisplay移除掉
        if (oldFocusedWindowHandle != nullptr) {
            sp<InputChannel> focusedInputChannel =
                    getInputChannelLocked(oldFocusedWindowHandle->getToken());
            if (focusedInputChannel != nullptr) {
                CancelationOptions options(CancelationOptions::CANCEL_NON_POINTER_EVENTS,
                                           "focus left window");
                synthesizeCancelationEventsForInputChannelLocked(focusedInputChannel, options);
                // 新建一个FocusEntry加入到mInboundQueue去dispatch
                enqueueFocusEventLocked(*oldFocusedWindowHandle, false /*hasFocus*/);
            }
            // oldFocusedWindowHandle不为空时需要移除旧的
            mFocusedWindowHandlesByDisplay.erase(displayId);
        }
        // 走到这个流程，如果oldFocusedWindowHandle不为空，newFocusedWindowHandle为空，那么在findFocusedWindowTargetsLocked()中的focusedWindowHandle为空
        // 如果newFocusedWindowHandle不为空，更新mFocusedWindowHandlesByDisplay
        if (newFocusedWindowHandle != nullptr) {
            // 更新mFocusedWindowHandlesByDisplay，在findFocusedWindowTargetsLocked()时用到
            mFocusedWindowHandlesByDisplay[displayId] = newFocusedWindowHandle;
            // 新建一个FocusEntry加入到mInboundQueue去dispatch
            enqueueFocusEventLocked(*newFocusedWindowHandle, true /*hasFocus*/);
        }
        if (mFocusedDisplayId == displayId) {
            // 添加focusChanged到mCommandQueue，在dispatchOnce时会执行
            onFocusChangedLocked(oldFocusedWindowHandle, newFocusedWindowHandle);
        }
    }
    // ......
}

这个方法，是从WMS调过来的，主要流程如下图：

ANR可能得原因

设置focusedApplication和focusedWindow中间时间差太长，在这个时间差内发生了ANR

设置focusedApplication发生在，resumeTopActivity，也就是am_set_resumed_activity的时候。

设置focusedWindow发生在，onResume之后，调用WMS的addView添加完窗口之后。

window被设置成了no_focusable，无法响应焦点。

如果误将一个window设置成no_focusable，则窗口无法成为focusedWindow，也可能导致ANR的发生。

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