Separated async-task-operator code from texture browser GUI code.

blender_cloud/async_loop.py

@@ -130,6 +130,84 @@ class AsyncLoopModalOperator(bpy.types.Operator):
         return {'RUNNING_MODAL'}
 
 
+# noinspection PyAttributeOutsideInit
+class AsyncModalOperatorMixin:
+    async_task = None  # asyncio task for fetching thumbnails
+    signalling_future = None  # asyncio future for signalling that we want to cancel everything.
+    log = logging.getLogger('%s.AsyncModalOperatorMixin' % __name__)
+
+    _state = 'INITIALIZING'
+
+    def invoke(self, context, event):
+        context.window_manager.modal_handler_add(self)
+        self.timer = context.window_manager.event_timer_add(1 / 15, context.window)
+        return {'RUNNING_MODAL'}
+
+    def modal(self, context, event):
+        task = self.async_task
+
+        if self._state != 'EXCEPTION' and task and task.done() and not task.cancelled():
+            ex = task.exception()
+            if ex is not None:
+                self._state = 'EXCEPTION'
+                self.log.error('Exception while running task: %s', ex)
+                return {'RUNNING_MODAL'}
+
+        if self._state == 'QUIT':
+            self._finish(context)
+            return {'FINISHED'}
+
+        return {'PASS_THROUGH'}
+
+    def _finish(self, context):
+        self._stop_async_task()
+        context.window_manager.event_timer_remove(self.timer)
+
+    def _new_async_task(self, async_task: asyncio.coroutine, future: asyncio.Future = None):
+        """Stops the currently running async task, and starts another one."""
+
+        self.log.debug('Setting up a new task %r, so any existing task must be stopped', async_task)
+        self._stop_async_task()
+
+        # Download the previews asynchronously.
+        self.signalling_future = future or asyncio.Future()
+        self.async_task = asyncio.ensure_future(async_task)
+        self.log.debug('Created new task %r', self.async_task)
+
+        # Start the async manager so everything happens.
+        ensure_async_loop()
+
+    def _stop_async_task(self):
+        self.log.debug('Stopping async task')
+        if self.async_task is None:
+            self.log.debug('No async task, trivially stopped')
+            return
+
+        # Signal that we want to stop.
+        self.async_task.cancel()
+        if not self.signalling_future.done():
+            self.log.info("Signalling that we want to cancel anything that's running.")
+            self.signalling_future.cancel()
+
+        # Wait until the asynchronous task is done.
+        if not self.async_task.done():
+            self.log.info("blocking until async task is done.")
+            loop = asyncio.get_event_loop()
+            try:
+                loop.run_until_complete(self.async_task)
+            except asyncio.CancelledError:
+                self.log.info('Asynchronous task was cancelled')
+                return
+
+        # noinspection PyBroadException
+        try:
+            self.async_task.result()  # This re-raises any exception of the task.
+        except asyncio.CancelledError:
+            self.log.info('Asynchronous task was cancelled')
+        except Exception:
+            self.log.exception("Exception from asynchronous task")
+
+
 def register():
     bpy.utils.register_class(AsyncLoopModalOperator)