fix race condition in core bluetooth startup

core bluetooth has to wait until centralManagerDidUpdateState_ is called
and the state is CBManagerStatePoweredOn before any other bluetooth
functions can be used.

Since __init__ can't be async, this means we have to move the check
to the other async entry points of discovery and scanner.

bleak/backends/corebluetooth/CentralManagerDelegate.py

@@ -66,7 +66,7 @@ def init(self):
         self.connected_peripheral = None
         self._connection_state = CMDConnectionState.DISCONNECTED
 
-        self.ready = False
+        self.powered_on_event = asyncio.Event()
         self.devices = {}
 
         self.disconnected_callback = None
@@ -84,15 +84,19 @@ def compliant(self):
             CBCentralManagerDelegate
         )
 
-    @property
-    def enabled(self):
-        """Check if the bluetooth device is on and running"""
-        return self.central_manager.state() == CBManagerStatePoweredOn
-
     @property
     def isConnected(self) -> bool:
         return self._connection_state == CMDConnectionState.CONNECTED
 
+    async def waitForPowerOn_(self, timeout: float):
+        """
+        Waits for state to be CBManagerStatePoweredOn. This must be done before
+        attempting to do anything else.
+
+        Throws asyncio.TimeoutError if power on is not detected before timeout.
+        """
+        await asyncio.wait_for(self.powered_on_event.wait(), timeout)
+
     async def scanForPeripherals_(self, scan_options) -> List[CBPeripheral]:
         """
         Scan for peripheral devices
@@ -160,7 +164,10 @@ def centralManagerDidUpdateState_(self, centralManager):
         elif centralManager.state() == CBManagerStatePoweredOn:
             logger.debug("Bluetooth powered on")
 
-        self.ready = True
+        if centralManager.state() == CBManagerStatePoweredOn:
+            self.powered_on_event.set()
+        else:
+            self.powered_on_event.clear()
 
     def centralManager_didDiscoverPeripheral_advertisementData_RSSI_(
         self,

bleak/backends/corebluetooth/discovery.py

@@ -23,7 +23,9 @@ async def discover(timeout: float = 5.0, **kwargs) -> List[BLEDevice]:
         timeout (float): duration of scanning period
 
     """
-    if not _manager.enabled:
+    try:
+        await _manager.waitForPowerOn_(0.1)
+    except asyncio.TimeoutError:
         raise BleakError("Bluetooth device is turned off")
 
     scan_options = {"timeout": timeout}

bleak/backends/corebluetooth/scanner.py

@@ -34,13 +34,14 @@ class BleakScannerCoreBluetooth(BaseBleakScanner):
     def __init__(self, **kwargs):
         super(BleakScannerCoreBluetooth, self).__init__(**kwargs)
         self._manager = cbapp.central_manager_delegate
-
-        if not self._manager.enabled:
-            raise BleakError("Bluetooth device is turned off")
-
         self._timeout = kwargs.get("timeout", 5.0)
 
     async def start(self):
+        try:
+            await self._manager.waitForPowerOn_(0.1)
+        except asyncio.TimeoutError:
+            raise BleakError("Bluetooth device is turned off")
+
         # TODO: Evaluate if newer macOS than 10.11 has stopScan.
         if hasattr(self._manager, "stopScan_"):
             await self._manager.scanForPeripherals_()