core: replace workflow.kill_default with workflow.close_others

core/src/apps/common/mnemonic.py

@@ -57,9 +57,8 @@ def get_seed(passphrase: str = "", progress_bar: bool = True) -> bytes:
 
 def _start_progress() -> None:
     # Because we are drawing to the screen manually, without a layout, we
-    # should make sure that no other layout is running.  At this point, only
-    # the homescreen should be on, so shut it down.
-    workflow.kill_default()
+    # should make sure that no other layout is running.
+    workflow.close_others()
     t = Text("Please wait", ui.ICON_CONFIG)
     ui.draw_simple(t)
 

core/src/apps/common/passphrase.py

@@ -26,6 +26,7 @@ async def get(ctx: wire.Context) -> str:
 
 
 async def _request_from_user(ctx: wire.Context) -> str:
+    workflow.close_others()  # request exclusive UI access
     if storage.device.get_passphrase_always_on_device():
         passphrase = await _request_on_device(ctx)
     else:
@@ -69,7 +70,6 @@ async def _request_on_device(ctx: wire.Context) -> str:
 
 
 def _entry_dialog() -> None:
-    workflow.kill_default()
     text = Text("Passphrase entry", ICON_CONFIG)
     text.normal("Please type your", "passphrase on the", "connected host.")
     draw_simple(text)

core/src/trezor/ui/__init__.py

@@ -168,7 +168,8 @@ def draw_simple(t: Component) -> None:  # noqa: F405
     This function bypasses the UI workflow engine, so other layouts will not know
     that something was drawn over them. In particular, if no other Layout is shown
     in a workflow, the homescreen will not redraw when the workflow is finished.
-    Use `workflow.kill_default()` if you need to avoid this situation.
+    Make sure you use `workflow.close_others()` before invoking this function
+    (note that `workflow.close_others()` is implicitly called with `button_request()`).
     """
     backlight_fade(style.BACKLIGHT_DIM)
     display.clear()

core/src/trezor/workflow.py

@@ -3,7 +3,7 @@ import utime
 from trezor import log, loop
 
 if False:
-    from typing import Any, Callable, Dict, Optional, Set
+    from typing import Callable, Dict, Optional, Set
 
     IdleCallback = Callable[[], None]
 
@@ -20,7 +20,7 @@ tasks = set()  # type: Set[loop.spawn]
 
 # Default workflow task, if a default workflow is running.  Default workflow
 # is not contained in the `tasks` set above.
-default_task = None  # type: Optional[loop.Task]
+default_task = None  # type: Optional[loop.spawn]
 
 # Constructor for the default workflow.  Returns a workflow task.
 default_constructor = None  # type: Optional[Callable[[], loop.Task]]
@@ -78,12 +78,10 @@ def start_default() -> None:
     assert default_constructor is not None
 
     if not default_task:
-        default_task = default_constructor()
+        default_task = loop.spawn(default_constructor())
         if __debug__:
-            log.debug(__name__, "start default: %s", default_task)
-        # Schedule the default task.  Because the task can complete on its own,
-        # we need to reset the `default_task` global in a finalizer.
-        loop.schedule(default_task, None, None, _finalize_default)
+            log.debug(__name__, "start default: %s", default_task.task)
+        default_task.set_finalizer(_finalize_default)
     else:
         if __debug__:
             log.debug(__name__, "default already started")
@@ -110,17 +108,19 @@ def kill_default() -> None:
         if __debug__:
             log.debug(__name__, "close default")
         # We let the `_finalize_default` reset the global.
-        loop.close(default_task)
+        default_task.close()
 
 
 def close_others() -> None:
-    """Shut down all running tasks, except the one that is currently executing, and
-    restart the default."""
-    try:
-        kill_default()
+    """Request workflow (and UI) exclusivity: shut down all running tasks, except
+    the one that is currently executing.
+
+    If this is called from outside a registered workflow, it is equivalent to "close
+    all tasks". In that case, the default task will be restarted afterwards.
+    """
+    if default_task is not None and not default_task.is_running():
+        default_task.close()
         # if no other tasks are running, start_default will run immediately
-    except ValueError:
-        pass
 
     # we need a local copy of tasks because processing task.close() modifies
     # the global instance
@@ -131,39 +131,23 @@ def close_others() -> None:
     # if tasks were running, closing the last of them will run start_default
 
 
-def _finalize_default(task: loop.Task, value: Any) -> None:
+def _finalize_default(task: loop.spawn) -> None:
     """Finalizer for the default task. Cleans up globals and restarts the default
     in case no other task is running."""
     global default_task
 
-    if default_task is task:
+    assert default_task is task  # finalizer is closing something other than default?
+    assert default_constructor is not None  # it should always be configured
+
     if __debug__:
-            log.debug(__name__, "default closed: %s", task)
+        log.debug(__name__, "default closed: %s", task.task)
     default_task = None
 
     if not tasks:
         # No registered workflows are running and we are in the default task
         # finalizer, so when this function finished, nothing will be running.
         # We must schedule a new instance of the default now.
-            if default_constructor is not None:
         start_default()
-            else:
-                raise RuntimeError  # no tasks and no default constructor
-
-    else:
-        if __debug__:
-            log.warning(
-                __name__,
-                "default task does not match: task=%s, default_task=%s",
-                task,
-                default_task,
-            )
-
-
-# TODO
-# If required, a function `shutdown_default` should be written, that clears the
-# default constructor and shuts down the running default task.
-# We currently do not need such function, so I'm just noting how it should work.
 
 
 class IdleTimer: