aioble/server: Support singleton re-registration across restart cycles.

Enable a pattern where Service and Characteristic objects are created
once and re-registered via register_services() after each BLE radio
restart, avoiding per-cycle heap allocations on constrained targets.

Fix _register() consuming initial= values after first registration.
Fix _server_shutdown() not waking tasks blocked in written().
Fix _init_capture() guard mismatch with _server_shutdown() preventing
capture infrastructure rebuild after shutdown.
Add register_services() auto-rebuild of capture infrastructure.
Add ble_reregister multitest covering 3 stop/start cycles.

Signed-off-by: Andrew Leech <andrew.leech@planetinnovation.com.au>

Author: pi-anl

micropython/bluetooth/aioble/aioble/server.py

@@ -15,7 +15,7 @@
     register_irq_handler,
     GattError,
 )
-from .device import DeviceConnection, DeviceTimeout
+from .device import DeviceConnection, DeviceDisconnectedError, DeviceTimeout
 
 _registered_characteristics = {}
 
@@ -56,6 +56,10 @@ def _server_irq(event, data):
 
 def _server_shutdown():
     global _registered_characteristics
+    for characteristic in _registered_characteristics.values():
+        if hasattr(characteristic, "_write_event"):
+            characteristic._write_event.set()
+        characteristic._value_handle = None
     _registered_characteristics = {}
     if hasattr(BaseCharacteristic, "_capture_task"):
         BaseCharacteristic._capture_task.cancel()
@@ -84,7 +88,6 @@ def _register(self, value_handle):
         _registered_characteristics[value_handle] = self
         if self._initial is not None:
             self.write(self._initial)
-            self._initial = None
 
     # Read value from local db.
     def read(self):
@@ -100,13 +103,21 @@ def write(self, data, send_update=False):
         else:
             ble.gatts_write(self._value_handle, data, send_update)
 
-    # When the a capture-enabled characteristic is created, create the
+    # When a capture-enabled characteristic is created, create the
     # necessary events (if not already created).
+    # Guard on _capture_task (not _capture_queue) to match _server_shutdown()
+    # which guards on _capture_task. This ensures partial teardown (task gone
+    # but queue remains) self-heals instead of silently no-oping.
     @staticmethod
     def _init_capture():
-        if hasattr(BaseCharacteristic, "_capture_queue"):
+        if hasattr(BaseCharacteristic, "_capture_task"):
             return
-
+        # Clean up any partial state from incomplete shutdown
+        for attr in ("_capture_queue", "_capture_write_event", "_capture_consumed_event"):
+            try:
+                delattr(BaseCharacteristic, attr)
+            except AttributeError:
+                pass
         BaseCharacteristic._capture_queue = deque((), _WRITE_CAPTURE_QUEUE_LIMIT)
         BaseCharacteristic._capture_write_event = asyncio.ThreadSafeFlag()
         BaseCharacteristic._capture_consumed_event = asyncio.ThreadSafeFlag()
@@ -152,6 +163,9 @@ async def written(self, timeout_ms=None):
         with DeviceTimeout(None, timeout_ms):
             await self._write_event.wait()
 
+        if self._value_handle is None:
+            raise DeviceDisconnectedError
+
         # Return the write data and clear the stored copy.
         # In default usage this will be just the connection handle.
         # In capture mode this will be a tuple of (connection_handle, received_data)
@@ -338,3 +352,8 @@ def register_services(*services):
             for descriptor in characteristic.descriptors:
                 descriptor._register(service_handles[n])
                 n += 1
+
+    for characteristic in _registered_characteristics.values():
+        if characteristic.flags & _FLAG_WRITE_CAPTURE:
+            BaseCharacteristic._init_capture()
+            break

micropython/bluetooth/aioble/multitests/ble_reregister.py

@@ -0,0 +1,114 @@
+# Test that singleton service/characteristic instances can be re-registered
+# across multiple stop/start cycles without data loss.
+
+import sys
+
+# ruff: noqa: E402
+sys.path.append("")
+
+from micropython import const
+import machine
+import time
+
+import asyncio
+import aioble
+import bluetooth
+
+TIMEOUT_MS = 5000
+
+SERVICE_UUID = bluetooth.UUID("A5A5A5A5-FFFF-9999-1111-5A5A5A5A5A5A")
+CHAR_INITIAL_UUID = bluetooth.UUID("00000000-1111-2222-3333-444444444444")
+CHAR_WRITE_UUID = bluetooth.UUID("00000000-1111-2222-3333-555555555555")
+
+
+# Acting in peripheral role.
+async def instance0_task():
+    # Create service and characteristics ONCE (singleton pattern).
+    service = aioble.Service(SERVICE_UUID)
+    aioble.Characteristic(service, CHAR_INITIAL_UUID, read=True, initial=b"hello")
+    char_write = aioble.Characteristic(service, CHAR_WRITE_UUID, read=True, write=True)
+
+    multitest.globals(BDADDR=aioble.config("mac"))
+    multitest.next()
+
+    for i in range(3):
+        # Re-register the same service instances.
+        aioble.register_services(service)
+
+        # Write a cycle-specific value to the writable characteristic.
+        char_write.write("periph{}".format(i))
+
+        multitest.broadcast("connect-{}".format(i))
+
+        # Wait for central to connect.
+        print("advertise", i)
+        connection = await aioble.advertise(
+            20_000, adv_data=b"\x02\x01\x06\x04\xffMPY", timeout_ms=TIMEOUT_MS
+        )
+        print("connected", i)
+
+        # Wait for the central to write.
+        await char_write.written(timeout_ms=TIMEOUT_MS)
+        print("written", i)
+
+        # Wait for the central to disconnect.
+        await connection.disconnected(timeout_ms=TIMEOUT_MS)
+        print("disconnected", i)
+
+        # Shutdown aioble.
+        print("shutdown", i)
+        aioble.stop()
+
+        await asyncio.sleep_ms(100)
+
+
+def instance0():
+    try:
+        asyncio.run(instance0_task())
+    finally:
+        aioble.stop()
+
+
+# Acting in central role.
+async def instance1_task():
+    multitest.next()
+
+    for i in range(3):
+        multitest.wait("connect-{}".format(i))
+
+        # Connect to peripheral.
+        print("connect", i)
+        device = aioble.Device(*BDADDR)
+        connection = await device.connect(timeout_ms=TIMEOUT_MS)
+
+        # Discover characteristics.
+        service = await connection.service(SERVICE_UUID)
+        char_initial = await service.characteristic(CHAR_INITIAL_UUID)
+        char_write = await service.characteristic(CHAR_WRITE_UUID)
+
+        # Read the initial= characteristic — must be the same every cycle.
+        print("read initial", await char_initial.read(timeout_ms=TIMEOUT_MS))
+
+        # Read the writable characteristic — should have cycle-specific value.
+        print("read written", await char_write.read(timeout_ms=TIMEOUT_MS))
+
+        # Write to the writable characteristic.
+        print("write", i)
+        await char_write.write("central{}".format(i), response=True, timeout_ms=TIMEOUT_MS)
+
+        # Disconnect from peripheral.
+        print("disconnect", i)
+        await connection.disconnect(timeout_ms=TIMEOUT_MS)
+        print("disconnected", i)
+
+        # Shutdown aioble.
+        aioble.stop()
+
+        await asyncio.sleep_ms(100)
+
+
+def instance1():
+    try:
+        asyncio.run(instance1_task())
+    finally:
+        aioble.stop()

micropython/bluetooth/aioble/multitests/ble_reregister.py.exp

@@ -0,0 +1,35 @@
+--- instance0 ---
+advertise 0
+connected 0
+written 0
+disconnected 0
+shutdown 0
+advertise 1
+connected 1
+written 1
+disconnected 1
+shutdown 1
+advertise 2
+connected 2
+written 2
+disconnected 2
+shutdown 2
+--- instance1 ---
+connect 0
+read initial b'hello'
+read written b'periph0'
+write 0
+disconnect 0
+disconnected 0
+connect 1
+read initial b'hello'
+read written b'periph1'
+write 1
+disconnect 1
+disconnected 1
+connect 2
+read initial b'hello'
+read written b'periph2'
+write 2
+disconnect 2
+disconnected 2