[#2795] More fine-grained error handling in concurrent case fetching

These changes are necessary because we do not want a failure to resolve
a single case to abort the thread for the whole API group. If one case
fails, we should still try and return the cases that properly resolve.

src/open_inwoner/cms/cases/views/services.py

@@ -186,31 +186,41 @@ def get_cases(self) -> list[ZaakWithApiGroup]:
 
         return cases_with_api_group
 
-    def _get_cases_for_api_group(self, group: ZGWApiGroupConfig):
+    def _get_cases_for_api_group(self, group: ZGWApiGroupConfig) -> list[Zaak]:
         raw_cases = group.zaken_client.fetch_cases(
             **get_user_fetch_parameters(self.request)
         )
-        preprocessed_cases = self.resolve_cases(raw_cases, group)
-        return preprocessed_cases
+        resolved_cases = self.resolve_cases(raw_cases, group)
+
+        filtered_cases = [
+            case for case in resolved_cases if case.status and is_zaak_visible(case)
+        ]
+        filtered_cases.sort(key=lambda case: case.startdatum, reverse=True)
+        return filtered_cases
 
     def resolve_cases(
         self,
         cases: list[Zaak],
         group: ZGWApiGroupConfig,
     ) -> list[Zaak]:
+        resolved_cases = []
         with parallel(max_workers=self._thread_limits["resolve_case_list"]) as executor:
             futures = [
                 executor.submit(self.resolve_case, case, group) for case in cases
             ]
 
-            concurrent.futures.wait(futures, timeout=self._fetch_task_timeout)
-
-        cases = [case for case in cases if case.status and is_zaak_visible(case)]
-        cases.sort(key=lambda case: case.startdatum, reverse=True)
+            for task in concurrent.futures.as_completed(
+                futures, timeout=self._fetch_task_timeout
+            ):
+                try:
+                    resolved_case = task.result()
+                    resolved_cases.append(resolved_case)
+                except BaseException:
+                    logger.exception("Error while resolving case")
 
-        return cases
+        return resolved_cases
 
-    def resolve_case(self, case: Zaak, group: ZGWApiGroupConfig):
+    def resolve_case(self, case: Zaak, group: ZGWApiGroupConfig) -> Zaak:
         logger.debug("Resolving case %s with group %s", case.identificatie, group)
 
         functions = [
@@ -240,12 +250,12 @@ def resolve_case(self, case: Zaak, group: ZGWApiGroupConfig):
             for task in concurrent.futures.as_completed(
                 futures, timeout=self._fetch_task_timeout
             ):
-                if exc := task.exception():
-                    logger.error("Error in resolving case: %s", exc, stack_info=True)
-
-                update_case = task.result()
-                if hasattr(update_case, "__call__"):
-                    update_case(case)
+                try:
+                    update_case = task.result()
+                    if hasattr(update_case, "__call__"):
+                        update_case(case)
+                except BaseException:
+                    logger.exception("Error in resolving case", stack_info=True)
 
         try:
             zaaktype_config = ZaakTypeConfig.objects.filter_case_type(
@@ -271,6 +281,8 @@ def resolve_case(self, case: Zaak, group: ZGWApiGroupConfig):
                 exc_info=True,
             )
 
+        return case
+
     @staticmethod
     def _resolve_zaak_type(
         case: Zaak, *, client: CatalogiClient