Android第三方键盘getTextBeforeCursor()耗时引发ANR问题咨询

报错详情 #

Input dispatching timed out (e716b5 InputMethod (server) is not responding. Waited 10001ms for MotionEvent)

ANR调用栈：

at sun.misc.Unsafe.park (Native method)
  at java.util.concurrent.locks.LockSupport.parkNanos (LockSupport.java:230)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedNanos (AbstractQueuedSynchronizer.java:1063)
  at java.util.concurrent.locks.AbstractQueuedSynchronizer.tryAcquireSharedNanos (AbstractQueuedSynchronizer.java:1358)
  at java.util.concurrent.locks.CountDownLatch.await (CountDownLatch.java:278)
  at com.android.internal.inputmethod.CancellationGroup$Completable$ValueBase.await (CancellationGroup.java:143)
  at com.android.internal.inputmethod.CancellationGroup$Completable$Values.await (CancellationGroup.java:203)
  at com.android.internal.view.InputConnectionWrapper.getResultOrNull (InputConnectionWrapper.java:100)
  at com.android.internal.view.InputConnectionWrapper.getTextBeforeCursor (InputConnectionWrapper.java:137)
  at func.keyboard.InputAnalyzer.onKeyChar (InputAnalyzer.java:25)
  at ime.BaseIME.callAnalyzer (BaseIME.java:435)
  at ime.LegacyIME.onKeyChar (LegacyIME.java:340)
  at ime.BaseIME.onKey (BaseIME.java:213)
  at manager.KeyInputManager.onKey (KeyInputManager.java:75)
  at common.PointerTracker.detectAndSendKey (PointerTracker.java:544)
  at common.PointerTracker.onUpEvent (PointerTracker.java:390)
  at common.KeyboardBaseView.onUpEvent (KeyboardBaseView.java:2423)
  at common.KeyboardBaseView.sendOnXEvent (KeyboardBaseView.java:2385)
  at ui.keyboard.common.KeyboardBaseView.onTouchEvent (KeyboardBaseView.java:2369)
  at android.view.View.dispatchTouchEvent (View.java:15199)
  at android.view.ViewGroup.dispatchTransformedTouchEvent (ViewGroup.java:3920)
  at android.view.ViewGroup.dispatchTouchEvent (ViewGroup.java:3594)
  at android.view.ViewGroup.dispatchTransformedTouchEvent (ViewGroup.java:3920)
  at android.view.ViewGroup.dispatchTouchEvent (ViewGroup.java:3594)
  at android.view.ViewGroup.dispatchTransformedTouchEvent (ViewGroup.java:3920)
  at android.view.ViewGroup.dispatchTouchEvent (ViewGroup.java:3594)
  at android.view.ViewGroup.dispatchTransformedTouchEvent (ViewGroup.java:3920)
  at android.view.ViewGroup.dispatchTouchEvent (ViewGroup.java:3594)
  at android.view.ViewGroup.dispatchTransformedTouchEvent (ViewGroup.java:3920)
  at android.view.ViewGroup.dispatchTouchEvent (ViewGroup.java:3594)
  at android.view.ViewGroup.dispatchTransformedTouchEvent (ViewGroup.java:3920)
  at android.view.ViewGroup.dispatchTouchEvent (ViewGroup.java:3594)
  at android.view.ViewGroup.dispatchTransformedTouchEvent (ViewGroup.java:3920)
  at android.view.ViewGroup.dispatchTouchEvent (ViewGroup.java:3594)
  at android.view.ViewGroup.dispatchTransformedTouchEvent (ViewGroup.java:3920)
  at android.view.ViewGroup.dispatchTouchEvent (ViewGroup.java:3594)
  at android.view.ViewGroup.dispatchTransformedTouchEvent (ViewGroup.java:3920)
  at android.view.ViewGroup.dispatchTouchEvent (ViewGroup.java:3594)
  at com.android.internal.policy.DecorView.superDispatchTouchEvent (DecorView.java:915)
  at com.android.internal.policy.PhoneWindow.superDispatchTouchEvent (PhoneWindow.java:1957)
  at android.app.Dialog.dispatchTouchEvent (Dialog.java:1162)
  at android.inputmethodservice.SoftInputWindow.dispatchTouchEvent (SoftInputWindow.java:188)
  at com.android.internal.policy.DecorView.dispatchTouchEvent (DecorView.java:873)
  at android.view.View.dispatchPointerEvent (View.java:15458)
  at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent (ViewRootImpl.java:7457)
  at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess (ViewRootImpl.java:7233)
  at android.view.ViewRootImpl$InputStage.deliver (ViewRootImpl.java:6595)
  at android.view.ViewRootImpl$InputStage.onDeliverToNext (ViewRootImpl.java:6652)
  at android.view.ViewRootImpl$InputStage.forward (ViewRootImpl.java:6618)
  at android.view.ViewRootImpl$AsyncInputStage.forward (ViewRootImpl.java:6786)
  at android.view.ViewRootImpl$InputStage.apply (ViewRootImpl.java:6626)
  at android.view.ViewRootImpl$AsyncInputStage.apply (ViewRootImpl.java:6843)
  at android.view.ViewRootImpl$InputStage.deliver (ViewRootImpl.java:6599)
  at android.view.ViewRootImpl$InputStage.onDeliverToNext (ViewRootImpl.java:6652)
  at android.view.ViewRootImpl$InputStage.forward (ViewRootImpl.java:6618)
  at android.view.ViewRootImpl$InputStage.apply (ViewRootImpl.java:6626)
  at android.view.ViewRootImpl$InputStage.deliver (ViewRootImpl.java:6599)
  at android.view.ViewRootImpl.deliverInputEvent (ViewRootImpl.java:9880)
  at android.view.ViewRootImpl.doProcessInputEvents (ViewRootImpl.java:9718)
  at android.view.ViewRootImpl.enqueueInputEvent (ViewRootImpl.java:9671)
  at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent (ViewRootImpl.java:10014)
  at android.view.InputEventReceiver.dispatchInputEvent (InputEventReceiver.java:220)
  at android.os.MessageQueue.nativePollOnce (Native method)
  at android.os.MessageQueue.next (MessageQueue.java:335)
  at android.os.Looper.loop (Looper.java:206)
  at android.app.ActivityThread.main (ActivityThread.java:8653)
  at java.lang.reflect.Method.invoke (Native method)
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:602)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1130)

关联业务代码 #

class InputAnalyzer { 
    ...

    fun onKeyChar(ic: InputConnection) {
        this.ic = ic
        if (!enabled)
            return

        val inputText = ic.getTextBeforeCursor(16, 0) ?: return
        service.themeManager.animateFromText(inputText.toString())
    }
}

业务逻辑说明：用户触发按键抬起事件时，键盘应用会先向EditText发送字符，再调用getTextBeforeCursor()获取光标前文本用于单词联想功能。

问题根因 #

• InputConnection相关接口属于跨进程Binder调用，getTextBeforeCursor()需要向输入框所在的目标应用发起请求，等待目标应用主线程处理后才能返回结果，并非本地即时返回的方法。
• 现有代码直接在主线程（触摸抬起事件的执行链路属于UI主线程）同步调用该跨进程方法，一旦目标应用主线程卡顿、输入框逻辑阻塞，会直接卡住键盘应用的主线程，阻塞时长超过10秒就会触发输入事件分发超时的ANR。
• 堆栈中主线程卡在CountDownLatch.await()等待跨进程结果返回，和上述场景完全匹配。

修复方案 #

• 禁止在主线程同步调用InputConnection的取值类跨进程方法：将getTextBeforeCursor、getSelectedText、getTextAfterCursor这类可能阻塞的调用全部挪到IO工作线程执行，拿到结果后再切回主线程执行UI动画、联想词更新等逻辑。
• 增加超时兜底：即使在工作线程执行跨进程调用，也要设置合理超时（建议200ms以内），超时直接放弃本次请求，避免无限等待占用线程资源。Android 10及以上版本系统对InputConnection调用有默认超时限制，低版本需要自行实现超时逻辑。
• 本地维护输入缓存减少跨进程调用：键盘侧自行维护当前输入框的文本状态，用户按键输入、删除、选中文本时同步更新本地缓存，仅在检测到输入框存在非键盘触发的变更（如用户手动粘贴、剪切、外部修改文本）时，才主动调用InputConnection接口同步一次最新文本，从根源上降低跨进程调用频次。
• 触摸事件链路轻量化：onTouchEvent、onUp这类触摸回调中仅做基础事件分发，文本分析、联想请求、动画触发这类逻辑全部延后到下一帧或者工作线程执行，保证触摸事件在5ms内处理完成返回，不阻塞输入事件分发。

修复代码示例 #

// 分析逻辑使用独立IO协程域，不阻塞主线程
private val analyzerScope = CoroutineScope(Dispatchers.IO + SupervisorJob())
private const val IC_CALL_TIMEOUT = 200L

class InputAnalyzer { 
    // 本地缓存光标前文本，减少跨进程调用
    private var cachedTextBeforeCursor: CharSequence = ""
    ...

    fun onKeyChar(ic: InputConnection, pressedChar: Char) {
        this.ic = ic
        if (!enabled) return

        // 先更新本地缓存，优先用本地数据触发轻量逻辑
        cachedTextBeforeCursor = (cachedTextBeforeCursor.toString() + pressedChar).takeLast(16)
        
        // 异步执行跨进程同步和重逻辑
        analyzerScope.launch {
            runCatching {
                // 带超时执行跨进程调用，避免无限等待
                val latestText = withTimeoutOrNull(IC_CALL_TIMEOUT) {
                    ic.getTextBeforeCursor(16, 0)?.toString()
                }
                latestText?.let { cachedTextBeforeCursor = it }
                
                // 切回主线程执行UI相关操作
                withContext(Dispatchers.Main) {
                    service.themeManager.animateFromText(cachedTextBeforeCursor.toString())
                }
            }
        }
    }
}

内容的提问来源于stack exchange，提问作者Heegyu Kim