Basic caching infrastructure.

Rearchitect fixed input ports to support invalidation.
Simplified SystemOutput.
Get rid of unnecessary data structures in diagram context.
Moved FixInputPort to ContextBase.
Convert spring-mass test to take advantage of cached derivatives.
Modify depth sensor to use the cache.
Add validate step in context allocation.
Rename Freestanding -> Fixed.
Merge changes from PRs: dependency tracker, cache, cache entry,
  cloneable DiagramContinuous/DiscreteState, connect base classes,
  output port allocator context parameter removal, PR RobotLocomotion#8623,
  input port PR RobotLocomotion#8760, diagram output PR RobotLocomotion#8857, output port PR RobotLocomotion#8920.

bindings/pydrake/systems/framework_py_semantics.cc

@@ -178,7 +178,6 @@ void DefineFrameworkPySemantics(py::module m) {
 
     auto system_output = DefineTemplateClassWithDefault<SystemOutput<T>>(
         m, "SystemOutput", GetPyParam<T>());
-    DefClone(&system_output);
     system_output
       .def("get_num_ports", &SystemOutput<T>::get_num_ports)
       .def("get_data", &SystemOutput<T>::get_data,

bindings/pydrake/systems/framework_py_systems.cc

@@ -274,7 +274,9 @@ struct Impl {
              py::arg("input_port"), py::arg("output_port"))
         // Context.
         .def("CreateDefaultContext", &System<T>::CreateDefaultContext)
-        .def("AllocateOutput", &System<T>::AllocateOutput)
+        .def("AllocateOutput",
+             overload_cast_explicit<unique_ptr<SystemOutput<T>>>(
+                 &System<T>::AllocateOutput))
         .def(
             "EvalVectorInput",
             [](const System<T>* self, const Context<T>& arg1, int arg2) {

bindings/pydrake/systems/rgbd_camera_example.py

@@ -43,7 +43,7 @@
 # Allocate context and render.
 context = camera.CreateDefaultContext()
 context.FixInputPort(0, BasicVector(x))
-output = camera.AllocateOutput(context)
+output = camera.AllocateOutput()
 camera.CalcOutput(context, output)
 
 # Get images from computed output.

bindings/pydrake/systems/test/custom_test.py

@@ -103,7 +103,7 @@ def test_adder_execution(self):
         system = self._create_adder_system()
         context = system.CreateDefaultContext()
         self._fix_adder_inputs(context)
-        output = system.AllocateOutput(context)
+        output = system.AllocateOutput()
         self.assertEqual(output.get_num_ports(), 1)
         system.CalcOutput(context, output)
         value = output.get_vector_data(0).get_value()
@@ -354,7 +354,7 @@ def _DoCalcAbstractOutput(self, context, y_data):
 
             self.assertEqual(context.get_num_input_ports(), 1)
             context.FixInputPort(0, AbstractValue.Make(expected_input_value))
-            output = system.AllocateOutput(context)
+            output = system.AllocateOutput()
             self.assertEqual(output.get_num_ports(), 1)
             system.CalcOutput(context, output)
             value = output.get_data(0)

bindings/pydrake/systems/test/general_test.py

@@ -145,7 +145,7 @@ def test_simulator_ctor(self):
 
             def check_output(context):
                 # Check number of output ports and value for a given context.
-                output = system.AllocateOutput(context)
+                output = system.AllocateOutput()
                 self.assertEqual(output.get_num_ports(), 1)
                 system.CalcOutput(context, output)
                 if T == float:

bindings/pydrake/systems/test/primitives_test.py

@@ -156,7 +156,7 @@ def test_vector_pass_through(self):
         system = PassThrough(model_value.size())
         context = system.CreateDefaultContext()
         context.FixInputPort(0, model_value)
-        output = system.AllocateOutput(context)
+        output = system.AllocateOutput()
         input_eval = system.EvalVectorInput(context, 0)
         compare_value(self, input_eval, model_value)
         system.CalcOutput(context, output)
@@ -168,7 +168,7 @@ def test_abstract_pass_through(self):
         system = PassThrough(model_value)
         context = system.CreateDefaultContext()
         context.FixInputPort(0, model_value)
-        output = system.AllocateOutput(context)
+        output = system.AllocateOutput()
         input_eval = system.EvalAbstractInput(context, 0)
         compare_value(self, input_eval, model_value)
         system.CalcOutput(context, output)
@@ -183,7 +183,7 @@ def test_gain(self):
 
         for system in systems:
             context = system.CreateDefaultContext()
-            output = system.AllocateOutput(context)
+            output = system.AllocateOutput()
 
             def mytest(input, expected):
                 context.FixInputPort(0, BasicVector(input))
@@ -197,7 +197,7 @@ def mytest(input, expected):
     def test_saturation(self):
         system = Saturation((0., -1., 3.), (1., 2., 4.))
         context = system.CreateDefaultContext()
-        output = system.AllocateOutput(context)
+        output = system.AllocateOutput()
 
         def mytest(input, expected):
             context.FixInputPort(0, BasicVector(input))
@@ -212,7 +212,7 @@ def test_wrap_to_system(self):
         system = WrapToSystem(2)
         system.set_interval(1, 1., 2.)
         context = system.CreateDefaultContext()
-        output = system.AllocateOutput(context)
+        output = system.AllocateOutput()
 
         def mytest(input, expected):
             context.FixInputPort(0, BasicVector(input))
@@ -238,7 +238,7 @@ def test_multiplexer(self):
             port_size = sum([len(vec) for vec in case['data']])
             self.assertEqual(mux.get_output_port(0).size(), port_size)
             context = mux.CreateDefaultContext()
-            output = mux.AllocateOutput(context)
+            output = mux.AllocateOutput()
             num_ports = len(case['data'])
             self.assertEqual(context.get_num_input_ports(), num_ports)
             for j, vec in enumerate(case['data']):

bindings/pydrake/systems/test/rendering_test.py

@@ -147,7 +147,7 @@ def test_pose_aggregator(self):
 
         # - CalcOutput.
         context = aggregator.CreateDefaultContext()
-        output = aggregator.AllocateOutput(context)
+        output = aggregator.AllocateOutput()
 
         p1 = [0, 1, 2]
         pose1 = PoseVector()

bindings/pydrake/systems/test/test_util_py.cc

@@ -180,7 +180,7 @@ PYBIND11_MODULE(test_util, m) {
           state.CopyToVector() + dt * state_dot.CopyToVector());
     }
     // Calculate output.
-    auto output = system.AllocateOutput(*context);
+    auto output = system.AllocateOutput();
     system.CalcOutput(*context, output.get());
     return output;
   });

bindings/pydrake/test/automotive_test.py

@@ -139,7 +139,7 @@ def test_pure_pursuit(self):
         lane = rg.junction(0).segment(0).lane(0)
         pure_pursuit = PurePursuitController()
         context = pure_pursuit.CreateDefaultContext()
-        output = pure_pursuit.AllocateOutput(context)
+        output = pure_pursuit.AllocateOutput()
 
         # Fix the inputs.
         ld_value = framework.AbstractValue.Make(
@@ -189,7 +189,7 @@ def test_idm_controller(self):
             road_position_strategy=RoadPositionStrategy.kExhaustiveSearch,
             period_sec=0.)
         context = idm.CreateDefaultContext()
-        output = idm.AllocateOutput(context)
+        output = idm.AllocateOutput()
 
         # Fix the inputs.
         pose_vector1 = PoseVector()
@@ -235,7 +235,7 @@ def test_simple_car(self):
         simple_car = SimpleCar()
         simulator = Simulator(simple_car)
         context = simulator.get_mutable_context()
-        output = simple_car.AllocateOutput(context)
+        output = simple_car.AllocateOutput()
 
         # Fix the input.
         command = DrivingCommand()

systems/controllers/qp_inverse_dynamics/qp_output_translator_system.cc

@@ -28,8 +28,6 @@ void QpOutputTranslatorSystem::CalcActuationTorques(
   // Output:
   auto out_vector = output->get_mutable_value();
 
-  // TODO(sherm1) This computation should be cached so it will be evaluated
-  // when first requested and then available for re-use.
   out_vector = robot_.B.transpose() * qp_output->dof_torques();
 
   DRAKE_ASSERT(out_vector.size() == robot_.get_num_actuators());

systems/controllers/qp_inverse_dynamics/qp_output_translator_system.h

@@ -54,7 +54,6 @@ class QpOutputTranslatorSystem : public systems::LeafSystem<double> {
    * selection matrix that maps the actuator indices to the generalized
    * coordinate indices.
    */
-  // TODO(sherm1) This should be cached so it doesn't need to be recomputed.
   void CalcActuationTorques(const systems::Context<double>& context,
                             systems::BasicVector<double>* output) const;
 

systems/framework/BUILD.bazel

@@ -295,6 +295,7 @@ drake_cc_library(
     srcs = ["output_port_value.cc"],
     hdrs = ["output_port_value.h"],
     deps = [
+        ":framework_common",
         ":value",
         ":value_checker",
         ":vector",
@@ -310,7 +311,6 @@ drake_cc_library(
     hdrs = ["context.h"],
     deps = [
         ":context_base",
-        ":output_port_value",
         ":parameters",
         ":state",
         "//common:default_scalars",
@@ -324,15 +324,14 @@ drake_cc_library(
     srcs = ["leaf_context.cc"],
     hdrs = ["leaf_context.h"],
     deps = [
-        ":cache_and_dependency_tracker",
         ":context",
-        ":parameters",
         ":vector",
         "//common:default_scalars",
         "//common:essential",
     ],
 )
 
+# TODO(sherm1) This should be "input_port".
 drake_cc_library(
     name = "input_port_descriptor",
     srcs = [
@@ -381,6 +380,7 @@ drake_cc_library(
         ":event_collection",
         ":input_port_descriptor",
         ":output_port",
+        ":output_port_value",
         ":system_base",
         ":system_constraint",
         ":system_scalar_converter",
@@ -400,7 +400,7 @@ drake_cc_library(
     srcs = ["leaf_output_port.cc"],
     hdrs = ["leaf_output_port.h"],
     deps = [
-        ":framework_common",
+        ":leaf_context",
         ":output_port",
         ":value",
         ":vector",
@@ -600,7 +600,6 @@ drake_cc_googletest(
 drake_cc_googletest(
     name = "cache_test",
     deps = [
-        ":cache_and_dependency_tracker",
         ":context_base",
         "//common:essential",
         "//systems/framework/test_utilities",
@@ -782,6 +781,7 @@ drake_cc_googletest(
     deps = [
         ":output_port_value",
         "//common:essential",
+        "//systems/framework/test_utilities",
     ],
 )
 

systems/framework/cache.cc

@@ -79,19 +79,29 @@ CacheEntryValue& Cache::CreateNewCacheEntryValue(
                           nullptr /* no value yet */));
   CacheEntryValue& value = *store_[index];
 
-  // Allocate a DependencyTracker for this cache entry. Note that a pointer
-  // to the new CacheEntryValue is retained so must have a lifetime matching
-  // the tracker. That requires that the Cache and DependencyGraph are contained
-  // in the same Context.
-  DependencyTracker& tracker = trackers->CreateNewDependencyTracker(
-      ticket,
-      "cache " + description,
-      &value);
+  // If no well-known DependencyTracker has been created for this cache entry,
+  // create a new one.
+  DependencyTracker* tracker{};
+  if (trackers->has_tracker(ticket)) {
+    // This should only have been done for built-in trackers.
+    DRAKE_DEMAND(ticket < internal::kNextAvailableTicket);
+    tracker = &trackers->get_mutable_tracker(ticket);
+    tracker->set_cache_entry_value(&value);
+  } else {
+    // Allocate a DependencyTracker for this cache entry. Note that a pointer
+    // to the new CacheEntryValue is retained so must have a lifetime matching
+    // the tracker. That requires that the Cache and DependencyGraph are
+    // contained in the same Context.
+    tracker = &trackers->CreateNewDependencyTracker(
+        ticket,
+        "cache " + description,
+        &value);
+  }
 
   // Subscribe to prerequisites (trackers must already exist).
   for (auto prereq : prerequisites) {
     auto& prereq_tracker = trackers->get_mutable_tracker(prereq);
-    tracker.SubscribeToPrerequisite(&prereq_tracker);
+    tracker->SubscribeToPrerequisite(&prereq_tracker);
   }
   return value;
 }