Android切換希臘語藍牙打開失敗

版本：Android 9
平臺：RK-PX30

問題描述：在狀態欄點擊藍牙圖標打開藍牙時，發現打開失敗，進入到設置里打開藍牙卻能打開成功，但是時間會比較長。

分析：
查看日誌發現，執行BluetoothHci::initialize()後，在獲取到藍牙MAC地址，就又把藍牙關閉了。測試發現如果把藍牙開啟超時時間設置長點就可以正常打開了（由原本的4s改為10s）。

2021-10-27 14:32:30.561 495-522/system_process D/BluetoothManagerService: MESSAGE_BLUETOOTH_STATE_CHANGE: OFF > BLE_TURNING_ON
2021-10-27 14:32:30.561 495-522/system_process D/BluetoothManagerService: Sending BLE State Change: OFF > BLE_TURNING_ON
2021-10-27 14:32:30.561 19461-19482/com.android.bluetooth D/BluetoothAdapterService: bleOnProcessStart()
2021-10-27 14:32:30.564 19461-19482/com.android.bluetooth D/BluetoothAdapterService: bleOnProcessStart() - Make Bond State Machine
2021-10-27 14:32:30.565 19461-19482/com.android.bluetooth D/BluetoothBondStateMachine: make
2021-10-27 14:32:30.570 19461-19497/com.android.bluetooth I/BluetoothBondStateMachine: StableState(): Entering Off State
2021-10-27 14:32:30.595 19461-19461/com.android.bluetooth D/BluetoothAdapterService: getAdapterService() - returning com.android.bluetooth.btservice.AdapterService@e8fb3e7
2021-10-27 14:32:30.600 19461-19461/com.android.bluetooth D/BluetoothAdapterService: getAdapterService() - returning com.android.bluetooth.btservice.AdapterService@e8fb3e7
2021-10-27 14:32:30.613 19461-19461/com.android.bluetooth D/BluetoothAdapterService: getAdapterService() - returning com.android.bluetooth.btservice.AdapterService@e8fb3e7
2021-10-27 14:32:30.615 19461-19461/com.android.bluetooth D/BluetoothAdapterService: handleMessage() - Message: 2
2021-10-27 14:32:30.615 19461-19461/com.android.bluetooth D/BluetoothAdapterService: handleMessage() - MESSAGE_PROFILE_SERVICE_REGISTERED
2021-10-27 14:32:30.616 19461-19461/com.android.bluetooth D/BluetoothAdapterService: handleMessage() - Message: 1
2021-10-27 14:32:30.616 19461-19461/com.android.bluetooth D/BluetoothAdapterService: handleMessage() - MESSAGE_PROFILE_SERVICE_STATE_CHANGED
2021-10-27 14:32:30.628 19461-19502/com.android.bluetooth I/bt_hci: hci_initialize: IBluetoothHci::getService() returned 0x76f4876c60 (remote)
2021-10-27 14:32:30.628 260-260/? I/[email protected]: BluetoothHci::initialize()  # 初始化
2021-10-27 14:32:34.566 19461-19482/com.android.bluetooth D/BluetoothAdapterService: updateAdapterState() - Broadcasting state BLE_TURNING_OFF to 1 receivers.
2021-10-27 14:32:34.567 495-522/system_process D/BluetoothManagerService: MESSAGE_BLUETOOTH_STATE_CHANGE: BLE_TURNING_ON > BLE_TURNING_OFF
2021-10-27 14:32:34.567 495-522/system_process D/BluetoothManagerService: Sending BLE State Change: BLE_TURNING_ON > BLE_TURNING_OFF  # 從log的時間來看，過了大概4s就把藍牙狀態設置為關閉，代碼中超時時間就是4s
2021-10-27 14:32:34.742 495-495/system_process D/BluetoothManagerService: Bluetooth Adapter address changed to 0F:DD:CC:AA:EE:0A  # 調用的initialize()  4s後才返回結果，但此時狀態已經設置為BLE_TURNING_OFF了
2021-10-27 14:32:34.743 495-495/system_process D/BluetoothManagerService: Stored Bluetoothaddress: 0F:DD:CC:AA:EE:0A
2021-10-27 14:32:34.744 495-495/system_process D/BluetoothManagerService: Bluetooth Adapter name changed to IPPhone
2021-10-27 14:32:34.747 495-495/system_process D/BluetoothManagerService: Stored Bluetooth name: IPPhone
2021-10-27 14:32:34.759 19461-19461/com.android.bluetooth D/BluetoothAdapterService: handleMessage() - Message: 1
2021-10-27 14:32:34.759 19461-19461/com.android.bluetooth D/BluetoothAdapterService: handleMessage() - MESSAGE_PROFILE_SERVICE_STATE_CHANGED
2021-10-27 14:32:34.760 19461-19461/com.android.bluetooth D/BluetoothAdapterService: handleMessage() - Message: 3
2021-10-27 14:32:34.760 19461-19461/com.android.bluetooth D/BluetoothAdapterService: handleMessage() - MESSAGE_PROFILE_SERVICE_UNREGISTERED
2021-10-27 14:32:34.761 19461-19482/com.android.bluetooth D/BluetoothAdapterService: updateAdapterState() - Broadcasting state OFF to 1 receivers.
2021-10-27 14:32:34.761 495-522/system_process D/BluetoothManagerService: MESSAGE_BLUETOOTH_STATE_CHANGE: BLE_TURNING_OFF > OFF

繼續分析，其他語言使用都正常，為什麼只有希臘語會有出現這種情況呢？

對比正常情況，BluetoothHci::initialize()調用後在2s內就會返回結果，因此問題就在於希臘語下BluetoothHci::initialize()的時間過長，這種問題最簡單的分析方法就是在可能有耗時較長的地方加log列印時間。
logcat本身會列印時間，如果是沒有列印時間的，就需要使用其他方式計算時間了。

最後定位到源碼里packages/apps/Bluetooth/src/com/android/bluetooth/Utils.java的getAddressStringFromByte()方法。
這個方法裡面很簡單，就只是調用了format()方法，但是該方法卻卡了至少2~4s的時間，加上其他步驟本身就需要接近2s，而上層BLE開啟的超時時間是4s，因此很容易就導致超時而打不開。

繼續跟蹤format()方法的實現：

format() # libcore/ojluni/src/main/java/java/util/Formatter.java
  ` toString()
    ` toUpperCase() # libcore/libart/src/main/java/java/lang/CaseMapper.java

最終找到根本原因是使用了希臘語的toUpperCase()方法。
該方法實現如下：

public static String toUpperCase(Locale locale, String s, int count) {
    String languageCode = locale.getLanguage();
    if (languageCode.equals("tr") || languageCode.equals("az") || languageCode.equals("lt")) {
        return ICU.toUpperCase(s, locale);
    }
    if (languageCode.equals("el")) { // 希臘語使用特殊方法處理
        return EL_UPPER.get().transliterate(s);
    }
}

private static final ThreadLocal<Transliterator> EL_UPPER = new ThreadLocal<Transliterator>() {
    @Override protected Transliterator initialValue() {
        return Transliterator.getInstance("el-Upper");
    }
};

android使用開源轉換庫icu做處理，在調用希臘語轉換模塊的時候需要生成大量的對象，因此第一次調用會有很明顯的延遲。
經過驗證，如果對toUpperCase()指定其他語言，也不會存在延遲；並且其他APP第一次調用該方法，也會有延遲。

解決方案：我們的解決方案是提前創建該對象，使用的時候就不會有延遲了。