OpenMM runner fails with more verbosity (#20)

When the simulation fails in the OpenMM runner, it may appear as just a
freeze with no explanation. This is because the simulation would fail on
a separate thread. This commit adds prints in the simulation thread, so
the cause of the failure appears somewhere.

This is a workaround and it should be solved in a better way. If the
simulation fails, it should cause the server to stop with a proper error
message. See #19.

python-libraries/narupa-openmm/src/narupa/openmm/imd.py

@@ -143,13 +143,17 @@ def report(self, simulation: app.Simulation, state: mm.State) -> None:
         if simulation.currentStep % self.frame_interval == 0:
             if positions is None:
                 positions = state.getPositions(asNumpy=True)
-            frame_data = openmm_to_frame_data(
-                state=state, topology=None, include_positions=False
-            )
-            frame_data.particle_positions = positions
-            frame_data.user_energy = self._total_user_energy
-            self.frame_publisher.send_frame(self._frame_index, frame_data)
-            self._frame_index += 1
+            try:
+                frame_data = openmm_to_frame_data(
+                    state=state, topology=None, include_positions=False
+                )
+            except Exception as err:
+                print(f"Error while building a frame: {err}")
+            else:
+                frame_data.particle_positions = positions
+                frame_data.user_energy = self._total_user_energy
+                self.frame_publisher.send_frame(self._frame_index, frame_data)
+                self._frame_index += 1
 
     def _on_first_frame(self, simulation: app.Simulation):
         """
@@ -161,8 +165,12 @@ def _on_first_frame(self, simulation: app.Simulation):
         if self._frame_index == 0:
             state = simulation.context.getState(getPositions=True, getEnergy=True)
             topology = simulation.topology
-            frame_data = openmm_to_frame_data(state=state, topology=topology)
-            self.frame_publisher.send_frame(self._frame_index, frame_data)
+            try:
+                frame_data = openmm_to_frame_data(state=state, topology=topology)
+            except Exception as err:
+                print(f"Error with the first frame: {err}")
+            else:
+                self.frame_publisher.send_frame(self._frame_index, frame_data)
 
     @staticmethod
     def get_masses(system: mm.System) -> np.ndarray:

python-libraries/narupa-openmm/src/narupa/openmm/runner.py

@@ -296,23 +296,26 @@ def run(
             self._run_task = self.threads.submit(self._run, steps)
 
     def _run(self, steps: Optional[int]) -> None:
-        remaining_steps = steps if steps is not None else float("inf")
-        for _ in self._variable_interval_generator.yield_interval():
-            if self._cancelled or remaining_steps <= 0:
-                break
-            steps_for_this_iteration = min(self.frame_interval, remaining_steps)
-            try:
-                self.simulation.step(steps_for_this_iteration)
-            except (ValueError, openmm.OpenMMException):
-                # We want to stop running if the simulation exploded in a way
-                # that prevents OpenMM to run. Otherwise, we will be a a state
-                # where OpenMM raises an exception which would make the runner
-                # unusable. The OpenMMException is typically raised by OpenMM
-                # itself when something is NaN; the ValueError is typically
-                # raised by the StateReporter when the energy is NaN.
-                break
-            remaining_steps -= steps_for_this_iteration
-        self._cancelled = False
+        try:
+            remaining_steps = steps if steps is not None else float("inf")
+            for _ in self._variable_interval_generator.yield_interval():
+                if self._cancelled or remaining_steps <= 0:
+                    break
+                steps_for_this_iteration = min(self.frame_interval, remaining_steps)
+                try:
+                    self.simulation.step(steps_for_this_iteration)
+                except (ValueError, openmm.OpenMMException):
+                    # We want to stop running if the simulation exploded in a way
+                    # that prevents OpenMM to run. Otherwise, we will be a a state
+                    # where OpenMM raises an exception which would make the runner
+                    # unusable. The OpenMMException is typically raised by OpenMM
+                    # itself when something is NaN; the ValueError is typically
+                    # raised by the StateReporter when the energy is NaN.
+                    break
+                remaining_steps -= steps_for_this_iteration
+            self._cancelled = False
+        except Exception as err:
+            print(f"Error whith run: {err}")
 
     def step(self):
         with self._cancel_lock: