introduce a helper for a restartable task

(there are going to be a few of these)

subiquity/async_helpers.py

@@ -16,11 +16,43 @@
 import asyncio
 
 
+def _done(fut):
+    try:
+        fut.result()
+    except asyncio.CancelledError:
+        pass
+
+
 def schedule_task(coro):
     loop = asyncio.get_event_loop()
-    loop.call_soon(asyncio.ensure_future, coro)
+    if asyncio.iscoroutine(coro):
+        task = asyncio.Task(coro)
+    else:
+        task = coro
+    task.add_done_callback(_done)
+    loop.call_soon(asyncio.ensure_future, task)
+    return task
 
 
 async def run_in_thread(func, *args):
     loop = asyncio.get_event_loop()
     return await loop.run_in_executor(None, func, *args)
+
+
+class SingleInstanceTask:
+
+    def __init__(self, func):
+        self.func = func
+        self.task = None
+
+    async def start(self, *args, **kw):
+        if self.task is not None:
+            self.task.cancel()
+            try:
+                await self.task
+            except asyncio.CancelledError:
+                pass
+        self.task = schedule_task(self.func(*args, **kw))
+
+    def start_sync(self, *args, **kw):
+        return schedule_task(self.start(*args, **kw))

subiquitycore/controllers/network.py

@@ -34,7 +34,7 @@ from subiquitycore.utils import (
 from subiquitycore.file_util import write_file
 from subiquitycore import netplan
 
-from subiquity.async_helpers import schedule_task
+from subiquity.async_helpers import SingleInstanceTask
 
 
 log = logging.getLogger("subiquitycore.controller.network")
@@ -129,7 +129,7 @@ class NetworkController(BaseController):
         self.model = app.base_model.network
         self.view = None
         self.view_shown = False
-        self.apply_config_task = None
+        self.apply_config_task = SingleInstanceTask(self._apply_config)
         if self.opts.dry_run:
             self.root = os.path.abspath(".subiquity")
             netplan_path = self.netplan_path
@@ -282,7 +282,7 @@ class NetworkController(BaseController):
             self.update_initial_configs()
         self.view = NetworkView(self.model, self)
         if not self.view_shown:
-            self.apply_config_start()
+            self.apply_config(silent=True)
             self.view_shown = True
         self.network_event_receiver.view = self.view
         self.ui.set_body(self.view)
@@ -298,18 +298,8 @@ class NetworkController(BaseController):
             netplan_config_file_name = '00-snapd-config.yaml'
         return os.path.join(self.root, 'etc/netplan', netplan_config_file_name)
 
-    def apply_config_start(self, silent=False):
-        schedule_task(self.apply_config(silent))
-
-    async def apply_config(self, silent):
-        if self.apply_config_task is not None:
-            self.apply_config_task.cancel()
-            try:
-                await self.apply_config_task
-            except asyncio.CancelledError:
-                pass
-        self.apply_config_task = asyncio.ensure_future(
-            self._apply_config(silent))
+    def apply_config(self, silent=False):
+        self.apply_config_task.start_sync(silent)
 
     async def _down_devs(self, devs):
         for dev in devs:

subiquitycore/core.py

@@ -274,6 +274,7 @@ class AsyncioEventLoop(urwid.AsyncioEventLoop):
     def _exception_handler(self, loop, context):
         exc = context.get('exception')
         if exc:
+            log.debug("_exception_handler %r", exc)
             loop.stop()
             if not isinstance(exc, urwid.ExitMainLoop):
                 # Store the exc_info so we can re-raise after the loop stops

subiquitycore/ui/views/network.py

@@ -136,7 +136,7 @@ class NetworkView(BaseView):
         self.del_link(device)
         for dev in touched_devs:
             self.update_link(dev)
-        self.controller.apply_config_start()
+        self.controller.apply_config()
 
     def _action(self, sender, action, device):
         action, meth = action

subiquitycore/ui/views/network_configure_manual_interface.py

@@ -250,7 +250,7 @@ class EditNetworkStretchy(Stretchy):
             self.device.config['dhcp{v}'.format(v=self.ip_version)] = True
         else:
             log.debug("EditNetworkStretchy %s, disabled", self.ip_version)
-        self.parent.controller.apply_config_start()
+        self.parent.controller.apply_config()
         self.parent.update_link(self.device)
         self.parent.remove_overlay()
 
@@ -307,7 +307,7 @@ class AddVlanStretchy(Stretchy):
         dev = self.parent.controller.add_vlan(
             self.device, self.form.vlan.value)
         self.parent.new_link(dev)
-        self.parent.controller.apply_config_start()
+        self.parent.controller.apply_config()
 
     def cancel(self, sender=None):
         self.parent.remove_overlay()
@@ -487,7 +487,7 @@ class BondStretchy(Stretchy):
         for dev in touched_devices:
             self.parent.update_link(dev)
         self.parent.remove_overlay()
-        self.parent.controller.apply_config_start()
+        self.parent.controller.apply_config()
 
     def cancel(self, sender=None):
         self.parent.remove_overlay()