kill off run_in_bg and some related hacks

DESIGN.md

@@ -164,12 +164,6 @@ running things in the background and subiquity uses
 [trio](https://trio.readthedocs.io/en/stable/) has nicer APIs but is
 a bit too new for now.
 
-The older approach which is still present in the codebase is the `run_in_bg`
-function, which takes two functions: one that takes no arguments and is called
-in a background thread and a callback that takes one argument, and is called
-in the main/UI thread with a `concurrent.futures.Future` representing the
-result of calling the first function.
-
 A cast-iron rule: Only touch the UI from the main thread.
 
 ### Terminal things

subiquity/controllers/tests/test_filesystem.py

@@ -34,7 +34,7 @@ class Thing:
 
 
 class MiniApplication:
-    ui = signal = loop = run_in_bg = None
+    ui = signal = loop = None
     answers = {}
     opts = Thing()
     opts.dry_run = True

subiquitycore/controller.py

@@ -46,7 +46,6 @@ class BaseController(ABC):
             #    subiquity/controllers/installprogress.py
             self.debug_flags = os.environ.get('SUBIQUITY_DEBUG', '').split(',')
         self.loop = app.loop
-        self.run_in_bg = app.run_in_bg
         self.app = app
         self.answers = app.answers.get(self.name, {})
 

subiquitycore/core.py

@@ -13,7 +13,6 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-from concurrent import futures
 import fcntl
 import json
 import logging
@@ -373,29 +372,8 @@ class Application:
         self.signal = Signal()
         self.prober = prober
         self.loop = None
-        self.pool = futures.ThreadPoolExecutor(10)
         self.controllers = ControllerSet(self, self.controllers)
 
-    def run_in_bg(self, func, callback):
-        """Run func() in a thread and call callback on UI thread.
-
-        callback will be passed a concurrent.futures.Future containing
-        the result of func(). The result of callback is discarded. An
-        exception will crash the process so be careful!
-        """
-        fut = self.pool.submit(func)
-
-        def in_main_thread(ignored):
-            self.loop.remove_watch_pipe(pipe)
-            os.close(pipe)
-            callback(fut)
-
-        pipe = self.loop.watch_pipe(in_main_thread)
-
-        def in_random_thread(ignored):
-            os.write(pipe, b'x')
-        fut.add_done_callback(in_random_thread)
-
     def run_command_in_foreground(self, cmd, before_hook=None, after_hook=None,
                                   **kw):
         screen = self.loop.screen
@@ -652,9 +630,3 @@ class Application:
         except Exception:
             log.exception("Exception in controller.run():")
             raise
-        finally:
-            # concurrent.futures.ThreadPoolExecutor tries to join all
-            # threads before exiting. We don't want that and this
-            # ghastly hack prevents it.
-            from concurrent.futures import thread
-            thread._threads_queues = {}