Cannot enable Bluetooth after using airplane and Bluetooth tethering sequentially

The root cause is we can't unbind blue service when bluetooth isnot disbaled
Otherwise the bluedroid stack will be out of sync with bluetooth service
only unbind bluetoothservice, when bluetooth is at OFF state.

bug 7376846

Change-Id: If5a11926f77a1ac29e75cdddbf5e90d492179f43

Author: Zhihai Xu

services/java/com/android/server/BluetoothManagerService.java

@@ -982,14 +982,9 @@ private void bluetoothStateChangeHandler(int prevState, int newState) {
                 sendBluetoothStateCallback(isUp);
 
                 //If Bluetooth is off, send service down event to proxy objects, and unbind
-                if (!isUp) {
-                    //Only unbind with mEnable flag not set
-                    //For race condition: disable and enable back-to-back
-                    //Avoid unbind right after enable due to callback from disable
-                    if ((!mEnable) && (mBluetooth != null)) {
-                        sendBluetoothServiceDownCallback();
-                        unbindAndFinish();
-                    }
+                if (!isUp && canUnbindBluetoothService()) {
+                    sendBluetoothServiceDownCallback();
+                    unbindAndFinish();
                 }
             }
 
@@ -1037,4 +1032,22 @@ private boolean waitForOnOff(boolean on, boolean off) {
         Log.e(TAG,"waitForOnOff time out");
         return false;
     }
+
+    private boolean canUnbindBluetoothService() {
+        synchronized(mConnection) {
+            //Only unbind with mEnable flag not set
+            //For race condition: disable and enable back-to-back
+            //Avoid unbind right after enable due to callback from disable
+            //Only unbind with Bluetooth at OFF state
+            //Only unbind without any MESSAGE_BLUETOOTH_STATE_CHANGE message
+            try {
+                if (mEnable || (mBluetooth == null)) return false;
+                if (mHandler.hasMessages(MESSAGE_BLUETOOTH_STATE_CHANGE)) return false;
+                return (mBluetooth.getState() == BluetoothAdapter.STATE_OFF);
+            } catch (RemoteException e) {
+                Log.e(TAG, "getState()", e);
+            }
+        }
+        return false;
+    }
 }