Fix background callbacks progress not deleted after fetch.

CHANGELOG.md

@@ -14,6 +14,12 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - [#2417](https://github.com/plotly/dash/pull/2417) Disable the pytest plugin if `dash[testing]` not installed, fix [#946](https://github.com/plotly/dash/issues/946).
 - [#2417](https://github.com/plotly/dash/pull/2417) Do not swallow the original error to get the webdriver, easier to know what is wrong after updating the browser but the driver.
 
+## [UNRELEASED]
+
+## Fixed
+
+- [#2415](https://github.com/plotly/dash/pull/2415) Fix background callbacks progress not deleted after fetch.
+
 ## [2.8.1] - 2023-01-30
 
 ## Fixed

dash/long_callback/managers/celery_manager.py

@@ -98,6 +98,7 @@ def get_progress(self, key):
         progress_key = self._make_progress_key(key)
         progress_data = self.handle.backend.get(progress_key)
         if progress_data:
+            self.handle.backend.delete(progress_key)
             return json.loads(progress_data)
 
         return None

dash/long_callback/managers/diskcache_manager.py

@@ -127,7 +127,11 @@ def call_job_fn(self, key, job_fn, args, context):
 
     def get_progress(self, key):
         progress_key = self._make_progress_key(key)
-        return self.handle.get(progress_key)
+        progress_data = self.handle.get(progress_key)
+        if progress_data:
+            self.handle.delete(progress_key)
+
+        return progress_data
 
     def result_ready(self, key):
         return self.handle.get(key) is not None

tests/integration/long_callback/app_progress_delete.py

@@ -0,0 +1,45 @@
+from dash import Dash, Input, Output, State, html, clientside_callback
+import time
+
+from tests.integration.long_callback.utils import get_long_callback_manager
+
+long_callback_manager = get_long_callback_manager()
+handle = long_callback_manager.handle
+
+app = Dash(__name__, long_callback_manager=long_callback_manager)
+
+app.layout = html.Div(
+    [
+        html.Button("Start", id="start"),
+        html.Div(id="output"),
+        html.Div(id="progress-output"),
+        html.Div(0, id="progress-counter"),
+    ]
+)
+
+clientside_callback(
+    "function(_, previous) { return parseInt(previous) + 1;}",
+    Output("progress-counter", "children"),
+    Input("progress-output", "children"),
+    State("progress-counter", "children"),
+    prevent_initial_call=True,
+)
+
+
+@app.callback(
+    Output("output", "children"),
+    Input("start", "n_clicks"),
+    progress=Output("progress-output", "children"),
+    interval=200,
+    background=True,
+    prevent_initial_call=True,
+)
+def on_bg_progress(set_progress, _):
+    set_progress("start")
+    time.sleep(2)
+    set_progress("stop")
+    return "done"
+
+
+if __name__ == "__main__":
+    app.run_server(debug=True)

tests/integration/long_callback/test_basic_long_callback.py

@@ -538,3 +538,12 @@ def test_lcbc013_unordered_state_input(dash_duo, manager):
         dash_duo.find_element("#click").click()
 
         dash_duo.wait_for_text_to_equal("#output", "stored")
+
+
+def test_lcbc014_progress_delete(dash_duo, manager):
+    with setup_long_callback_app(manager, "app_progress_delete") as app:
+        dash_duo.start_server(app)
+        dash_duo.find_element("#start").click()
+        dash_duo.wait_for_text_to_equal("#output", "done")
+
+        assert dash_duo.find_element("#progress-counter").text == "2"