pybricks/util_pb/pb_task: Don't wait for cancel on shutdown.

Fixes pybricks/support#814 so the user can at
least turn the hub off without removing the batteries.

CHANGELOG.md

@@ -12,9 +12,12 @@
 - Reverted Pybricks Code stop button raises `SystemAbort` instead of
   `SystemExit` ([support#834]).
 - Improved stop message raised on `SystemExit` and `SystemAbort` ([support#836]).
+- Fixed Technic Hub and City Hub sometimes not shutting down when a Bluetooth
+  operation is busy ([support#814]).
 
 [support#777]: https://github.com/pybricks/support/issues/777
 [support#805]: https://github.com/pybricks/support/issues/805
+[support#834]: https://github.com/pybricks/support/issues/814
 [support#826]: https://github.com/pybricks/support/issues/826
 [support#834]: https://github.com/pybricks/support/issues/834
 [support#834]: https://github.com/pybricks/support/issues/836

pybricks/util_pb/pb_task.c

@@ -3,6 +3,7 @@
 
 #include <pbio/error.h>
 #include <pbio/task.h>
+#include <pbsys/status.h>
 
 #include "py/mpconfig.h"
 #include "py/mperrno.h"
@@ -41,7 +42,16 @@ void pb_wait_task(pbio_task_t *task, mp_int_t timeout) {
     } else {
         pbio_task_cancel(task);
 
-        while (task->status == PBIO_ERROR_AGAIN) {
+        while (task->status == PBIO_ERROR_AGAIN
+               #if !PYBRICKS_PY_COMMON_CHARGER
+               // HACK: This ensures we don't make the application program wait
+               // forever for a failed task cancellation when shutdown is
+               // requested. See https://github.com/pybricks/pybricks-micropython/pull/129
+               // We can remove this hack once we can ensure that task
+               // cancellation does not fail (for known cases).
+               && !pbsys_status_test(PBIO_PYBRICKS_STATUS_SHUTDOWN_REQUEST)
+               #endif
+               ) {
             MICROPY_VM_HOOK_LOOP
         }