Allow setting n_jobs on tool invocation

- It can be useful to set n_jobs indepently from the config file
- For the sklearn reconstructors this requires setting n_jobs on every
  model, that is attached to the reconstructor
- Fixes #2307

ctapipe/reco/reconstructor.py

@@ -70,7 +70,7 @@ class Reconstructor(TelescopeComponent):
     algorithms should inherit from
     """
 
-    #: ctapipe_rco entry points may provide Reconstructor implementations
+    #: ctapipe_reco entry points may provide Reconstructor implementations
     plugin_entry_point = "ctapipe_reco"
 
     def __init__(self, subarray, **kwargs):
@@ -141,6 +141,18 @@ def read(cls, path, parent=None, subarray=None, **kwargs):
         Provenance().add_input_file(path, role="reconstructor")
         return instance
 
+    def set_n_jobs(self, n_jobs):
+        """
+        Set n_jobs if applicable for the reconsructor.
+        This is not just a traits option of the class, because
+        for example in the case of the SKLearnReconstructors you need
+        to set the property of all of the sklearn models for it to be
+        applied in the fit and predict steps.
+        """
+        self.log.warning(
+            f"Trying to set n_jobs to {n_jobs}, but the reconstructor does not make any use of it."
+        )
+
 
 class HillasGeometryReconstructor(Reconstructor):
     """

ctapipe/reco/sklearn.py

@@ -222,6 +222,13 @@ def fit(self, key, table):
         y = self._table_to_y(table, mask=valid)
         self._models[key].fit(X, y)
 
+    def set_n_jobs(self, n_jobs):
+        """
+        Update n_jobs of all associated models.
+        """
+        for model in self._models.values():
+            setattr(model, "n_jobs", n_jobs)
+
 
 class SKLearnRegressionReconstructor(SKLearnReconstructor):
     """
@@ -803,6 +810,14 @@ def predict_table(self, key, table: Table) -> Dict[ReconstructionProperty, Table
             ReconstructionProperty.GEOMETRY: altaz_result,
         }
 
+    def set_n_jobs(self, n_jobs):
+        """
+        Update n_jobs of all associated models.
+        """
+        for (disp, sign) in self._models.values():
+            setattr(disp, "n_jobs", n_jobs)
+            setattr(sign, "n_jobs", n_jobs)
+
 
 class CrossValidator(Component):
     """Class to train sklearn based reconstructors in a cross validation"""

ctapipe/reco/tests/test_sklearn.py

@@ -9,6 +9,7 @@
 from ctapipe.core import Component
 from ctapipe.reco import EnergyRegressor, ParticleClassifier
 from ctapipe.reco.reconstructor import ReconstructionProperty
+from ctapipe.reco.sklearn import DispReconstructor
 
 KEY = "LST_LST_LSTCam"
 
@@ -166,6 +167,49 @@ def test_regressor_single_event(model_cls, example_table, example_subarray):
     assert valid[0] == False
 
 
+def test_set_n_jobs(example_subarray):
+    config = Config(
+        {
+            "EnergyRegressor": {
+                "model_cls": "RandomForestRegressor",
+                "model_config": {"n_estimators": 20, "max_depth": 15, "n_jobs": -1},
+            }
+        }
+    )
+    regressor = EnergyRegressor(
+        example_subarray,
+        config=config,
+    )
+
+    regressor._models["telescope"] = regressor._new_model()
+    assert regressor._models["telescope"].n_jobs == -1
+    regressor.set_n_jobs(42)
+    assert regressor._models["telescope"].n_jobs == 42
+
+    # DISP has two models per telescope, check that aswell
+    config = Config(
+        {
+            "DispReconstructor": {
+                "norm_cls": "RandomForestRegressor",
+                "norm_config": {"n_estimators": 20, "max_depth": 15, "n_jobs": -1},
+                "sign_cls": "RandomForestClassifier",
+                "sign_config": {"n_estimators": 20, "max_depth": 15, "n_jobs": -1},
+            }
+        }
+    )
+    disp = DispReconstructor(
+        example_subarray,
+        config=config,
+    )
+
+    disp._models["telescope"] = disp._new_models()
+    assert disp._models["telescope"][0].n_jobs == -1
+    assert disp._models["telescope"][1].n_jobs == -1
+    disp.set_n_jobs(42)
+    assert disp._models["telescope"][0].n_jobs == 42
+    assert disp._models["telescope"][1].n_jobs == 42
+
+
 @pytest.mark.parametrize(
     "model_cls", ["KNeighborsClassifier", "RandomForestClassifier"]
 )

ctapipe/tools/apply_models.py

@@ -68,6 +68,12 @@ class ApplyModels(Tool):
         help="How many subarray events to load at once for making predictions.",
     ).tag(config=True)
 
+    n_jobs = Integer(
+        default_value=None,
+        allow_none=True,
+        help="Number of threads to use for the reconstruction. This overwrites the values in the config",
+    ).tag(config=True)
+
     progress_bar = Bool(
         help="show progress bar during processing",
         default_value=True,
@@ -150,6 +156,9 @@ def setup(self):
             Reconstructor.read(path, parent=self, subarray=self.loader.subarray)
             for path in self.reconstructor_paths
         ]
+        if self.n_jobs:
+            for r in self._reconstructors:
+                r.set_n_jobs(self.n_jobs)
 
     def start(self):
         """Apply models to input tables"""

ctapipe/tools/train_disp_reconstructor.py

@@ -66,6 +66,12 @@ class TrainDispReconstructor(Tool):
         default_value=0, help="Random seed for sampling and cross validation"
     ).tag(config=True)
 
+    n_jobs = Int(
+        default_value=None,
+        allow_none=True,
+        help="Number of threads to use for the reconstruction. This overwrites the values in the config",
+    ).tag(config=True)
+
     project_disp = Bool(
         default_value=False,
         help=(
@@ -103,6 +109,9 @@ def setup(self):
         self.n_events.attach_subarray(self.loader.subarray)
 
         self.models = DispReconstructor(self.loader.subarray, parent=self)
+        if self.n_jobs:
+            self.models.set_n_jobs(self.n_jobs)
+
         self.cross_validate = CrossValidator(parent=self, model_component=self.models)
         self.rng = np.random.default_rng(self.random_seed)
         self.check_output(self.output_path, self.cross_validate.output_path)

ctapipe/tools/train_energy_regressor.py

@@ -63,6 +63,12 @@ class TrainEnergyRegressor(Tool):
         default_value=0, help="Random seed for sampling and cross validation"
     ).tag(config=True)
 
+    n_jobs = Int(
+        default_value=None,
+        allow_none=True,
+        help="Number of threads to use for the reconstruction. This overwrites the values in the config",
+    ).tag(config=True)
+
     aliases = {
         ("i", "input"): "TableLoader.input_url",
         ("o", "output"): "TrainEnergyRegressor.output_path",
@@ -94,6 +100,8 @@ def setup(self):
         self.n_events.attach_subarray(self.loader.subarray)
 
         self.regressor = EnergyRegressor(self.loader.subarray, parent=self)
+        if self.n_jobs:
+            self.regressor.set_n_jobs(self.n_jobs)
         self.cross_validate = CrossValidator(
             parent=self, model_component=self.regressor
         )

ctapipe/tools/train_particle_classifier.py

@@ -92,6 +92,12 @@ class TrainParticleClassifier(Tool):
         help="Random number seed for sampling and the cross validation splitting",
     ).tag(config=True)
 
+    n_jobs = Int(
+        default_value=None,
+        allow_none=True,
+        help="Number of threads to use for the reconstruction. This overwrites the values in the config",
+    ).tag(config=True)
+
     aliases = {
         "signal": "TrainParticleClassifier.input_url_signal",
         "background": "TrainParticleClassifier.input_url_background",
@@ -144,6 +150,8 @@ def setup(self):
         self.n_background.attach_subarray(self.subarray)
 
         self.classifier = ParticleClassifier(subarray=self.subarray, parent=self)
+        if self.n_jobs:
+            self.classifier.set_n_jobs(self.n_jobs)
         self.rng = np.random.default_rng(self.random_seed)
         self.cross_validate = CrossValidator(
             parent=self, model_component=self.classifier