Fix process-node handling by process monitor thread

To avoid SQLAlchemy session conflicts, the process node MUST be fetched on each request (not locally stored) to ensure any given thread will handle its OWN fetched process node.

src/aiidalab_qe/app/result/__init__.py

@@ -154,7 +154,7 @@ def _on_kill_button_click(self, _):
 
     def _on_update_results_button_click(self, _):
         self.node_view.node = None
-        self.node_view.node = self._model.process_node
+        self.node_view.node = self._model.get_process_node()
 
     def _on_clean_scratch_button_click(self, _):
         self._model.clean_remote_data()
@@ -164,9 +164,9 @@ def _update_kill_button_layout(self):
         if not self.rendered:
             return
         if (
-            not self._model.process
-            or self._model.process_node.is_finished
-            or self._model.process_node.is_excepted
+            not (process_node := self._model.get_process_node())
+            or process_node.is_finished
+            or process_node.is_excepted
             or self.state
             in (
                 self.State.SUCCESS,
@@ -180,31 +180,32 @@ def _update_kill_button_layout(self):
     def _update_clean_scratch_button_layout(self):
         if not self.rendered:
             return
-        if self._model.process and self._model.process_node.is_terminated:
+        process_node = self._model.get_process_node()
+        if process_node and process_node.is_terminated:
             self.clean_scratch_button.layout.display = "block"
         else:
             self.clean_scratch_button.layout.display = "none"
 
     def _update_state(self):
-        if not self._model.process:
+        if not (process_node := self._model.get_process_node()):
             self.state = self.State.INIT
-        elif self._model.process_node.process_state in (
+        elif process_node.process_state in (
             ProcessState.CREATED,
             ProcessState.RUNNING,
             ProcessState.WAITING,
         ):
             self.state = self.State.ACTIVE
             self._model.process_info = PROCESS_RUNNING
         elif (
-            self._model.process_node.process_state
+            process_node.process_state
             in (
                 ProcessState.EXCEPTED,
                 ProcessState.KILLED,
             )
-            or self._model.process_node.is_failed
+            or process_node.is_failed
         ):
             self.state = self.State.FAIL
             self._model.process_info = PROCESS_EXCEPTED
-        elif self._model.process_node.is_finished_ok:
+        elif process_node.is_finished_ok:
             self.state = self.State.SUCCESS
             self._model.process_info = PROCESS_COMPLETED

src/aiidalab_qe/app/result/model.py

@@ -5,6 +5,7 @@
 import traitlets as tl
 
 from aiida import orm
+from aiida.common.exceptions import NotExistent
 from aiida.engine.processes import control
 
 
@@ -14,25 +15,27 @@ class ResultsModel(tl.HasTraits):
     process_info = tl.Unicode("")
     process_remote_folder_is_clean = tl.Bool(False)
 
-    _process_node: orm.ProcessNode | None = None
-
     @property
     def process_node(self):
-        if self._process_node is None:
-            self._process_node = self._get_process_node()
-        return self._process_node
+        return self.get_process_node()
 
     def update(self):
         self._update_process_remote_folder_state()
 
+    def get_process_node(self):
+        try:
+            return orm.load_node(self.process) if self.process else None
+        except NotExistent:
+            return None
+
     def kill_process(self):
-        if process := self._get_process_node():
-            control.kill_processes([process])
+        if process_node := self.get_process_node():
+            control.kill_processes([process_node])
 
     def clean_remote_data(self):
-        if self.process_node is None:
+        if not (process_node := self.get_process_node()):
             return
-        for called_descendant in self.process_node.called_descendants:
+        for called_descendant in process_node.called_descendants:
             if isinstance(called_descendant, orm.CalcJobNode):
                 with contextlib.suppress(Exception):
                     called_descendant.outputs.remote_folder._clean()
@@ -42,14 +45,11 @@ def reset(self):
         self.process = None
         self.process_info = ""
 
-    def _get_process_node(self):
-        return orm.load_node(self.process) if self.process else None
-
     def _update_process_remote_folder_state(self):
-        if self.process_node is None:
+        if not (process_node := self.get_process_node()):
             return
         cleaned = []
-        for called_descendant in self.process_node.called_descendants:
+        for called_descendant in process_node.called_descendants:
             if isinstance(called_descendant, orm.CalcJobNode):
                 with contextlib.suppress(Exception):
                     cleaned.append(called_descendant.outputs.remote_folder.is_empty)

src/aiidalab_qe/plugins/xps/model.py

@@ -1,7 +1,7 @@
 import traitlets as tl
 
 from aiida.common import NotExistent
-from aiida.orm import Group, QueryBuilder, StructureData, load_group
+from aiida.orm import Group, QueryBuilder, load_group
 from aiidalab_qe.common.mixins import HasInputStructure
 from aiidalab_qe.common.panel import SettingsModel