Create a single cancel callback for each unique input.

Author: T4rk1n

dash/_callback.py

@@ -12,7 +12,6 @@
 from .exceptions import (
     PreventUpdate,
     WildcardInLongCallback,
-    DuplicateCallback,
     MissingLongCallbackManagerError,
     LongCallbackError,
 )
@@ -171,25 +170,8 @@ def callback(
             cancel_inputs = coerce_to_list(cancel)
             validate_long_inputs(cancel_inputs)
 
-            cancels_output = [Output(c.component_id, "id") for c in cancel_inputs]
-
-            try:
-
-                @callback(cancels_output, cancel_inputs, prevent_initial_call=True)
-                def cancel_call(*_):
-                    job_ids = flask.request.args.getlist("cancelJob")
-                    executor = (
-                        manager or context_value.get().background_callback_manager
-                    )
-                    if job_ids:
-                        for job_id in job_ids:
-                            executor.terminate_job(job_id)
-                    return NoUpdate()
-
-            except DuplicateCallback:
-                pass  # Already a callback to cancel, will get the proper jobs from the store.
-
             long_spec["cancel"] = [c.to_dict() for c in cancel_inputs]
+            long_spec["cancel_inputs"] = cancel_inputs
 
         if cache_args_to_ignore:
             long_spec["cache_args_to_ignore"] = cache_args_to_ignore

dash/dash.py

@@ -1316,6 +1316,30 @@ def _setup_server(self):
 
         _validate.validate_long_callbacks(self.callback_map)
 
+        cancels = set()
+
+        for callback in self.callback_map.values():
+            cancel = callback.get("long", {}).pop("cancel_inputs")
+            if cancel:
+                cancels.update(cancel)
+
+        if cancels:
+            for cancel_input in cancels:
+
+                # pylint: disable=cell-var-from-loop
+                @self.callback(
+                    Output(cancel_input.component_id, "id"),
+                    cancel_input,
+                    prevent_initial_call=True,
+                )
+                def cancel_call(*_):
+                    job_ids = flask.request.args.getlist("cancelJob")
+                    executor = _callback.context_value.get().background_callback_manager
+                    if job_ids:
+                        for job_id in job_ids:
+                            executor.terminate_job(job_id)
+                    return no_update
+
     def _add_assets_resource(self, url_path, file_path):
         res = {"asset_path": url_path, "filepath": file_path}
         if self.config.assets_external_path: