Add callbacks for synchronizing with C++ Solution members

Objects that need to hold pointers to the members of a C++ Solution,
like the Python Solution object or StFlow, can register a callback
with the Solution that will be called if any of the thermo/kinetics/transport
objects change.

Fixes #1409

include/cantera/base/Solution.h

@@ -108,6 +108,22 @@ public:
     //! Returns a null pointer if the requested handle does not exist.
     shared_ptr<ExternalHandle> getExternalHandle(const std::string& name) const;
 
+    //! Register a function to be called if any of the Solution's thermo, kinetics,
+    //! or transport objects is replaced.
+    //! @param id  A unique ID corresponding to the object affected by the callback.
+    //!   Typically, this is a pointer to an object that also holds a reference to the
+    //!   Solution object.
+    //! @param callback  The callback function to be called after any component of the
+    //!   Solution is replaced.
+    //! When the callback becomes invalid (for example, the corresponding object is
+    //! being deleted, the removeChangedCallback() method must be invoked.
+    //! @since New in Cantera 3.0
+    void registerChangedCallback(void* id, const function<void()>& callback);
+
+    //! Remove the callback function associated with the specified object.
+    //! @since New in Cantera 3.0
+    void removeChangedCallback(void* id);
+
 protected:
     shared_ptr<ThermoPhase> m_thermo;  //!< ThermoPhase manager
     shared_ptr<Kinetics> m_kinetics;  //!< Kinetics manager
@@ -124,6 +140,10 @@ protected:
     //! Wrappers for this Kinetics object in extension languages, for evaluation
     //! of user-defined reaction rates
     std::map<std::string, shared_ptr<ExternalHandle>> m_externalHandles;
+
+    //! Callback functions that are invoked when the therm, kinetics, or transport
+    //! members of the Solution are replaced.
+    map<void*, function<void()>> m_changeCallbacks;
 };
 
 //! Create and initialize a new Solution from an input file

include/cantera/oneD/StFlow.h

@@ -63,6 +63,8 @@ public:
     //! @param points  initial number of grid points
     StFlow(shared_ptr<Solution> sol, const std::string& id="", size_t points=1);
 
+    ~StFlow();
+
     //! @name Problem Specification
     //! @{
 
@@ -440,11 +442,6 @@ protected:
     Kinetics* m_kin;
     Transport* m_trans;
 
-    // Smart pointer preventing garbage collection when the transport model of an
-    // associated Solution object changes: the transport model of the StFlow object
-    // will remain unaffected by an external change.
-    shared_ptr<Transport> m_trans_shared;
-
     // boundary emissivities for the radiation calculations
     doublereal m_epsilon_left;
     doublereal m_epsilon_right;

interfaces/cython/cantera/delegator.pxd

@@ -84,3 +84,4 @@ cdef extern from "cantera/base/ExtensionManagerFactory.h" namespace "Cantera":
 ctypedef CxxDelegator* CxxDelegatorPtr
 
 cdef int assign_delegates(object, CxxDelegator*) except -1
+cdef void callback_v(PyFuncInfo& funcInfo)

interfaces/cython/cantera/solutionbase.pxd

@@ -59,6 +59,8 @@ cdef extern from "cantera/base/Solution.h" namespace "Cantera":
         size_t nAdjacent()
         shared_ptr[CxxSolution] adjacent(size_t)
         void holdExternalHandle(string&, shared_ptr[CxxExternalHandle])
+        void registerChangedCallback(void*, function[void()])
+        void removeChangedCallback(void*)
 
     cdef shared_ptr[CxxSolution] CxxNewSolution "Cantera::Solution::create" ()
     cdef shared_ptr[CxxSolution] newSolution (
@@ -86,4 +88,5 @@ cdef class _SolutionBase:
     cdef np.ndarray _selected_species
     cdef object parent
     cdef object _adjacent
+    cdef object _soln_changed_callback
     cdef public object _references

interfaces/cython/cantera/solutionbase.pyx

@@ -13,6 +13,7 @@ from .kinetics cimport *
 from .transport cimport *
 from .reaction cimport *
 from ._utils cimport *
+from .delegator cimport pyOverride, callback_v
 from .yamlwriter cimport YamlWriter
 
 ctypedef CxxSurfPhase* CxxSurfPhasePtr
@@ -110,6 +111,10 @@ cdef class _SolutionBase:
         if name is not None:
             self.name = name
 
+    def __dealloc__(self):
+        if self.base != NULL:
+            self.base.removeChangedCallback(<PyObject*>self)
+
     property name:
         """
         The name assigned to this object. The default value corresponds
@@ -429,11 +434,22 @@ cdef _assign_Solution(_SolutionBase soln, shared_ptr[CxxSolution] cxx_soln,
     if not weak:
         # When the main application isn't Python, we should only hold a weak reference
         # here, since the C++ Solution object owns this Python Solution.
+        if soln._base.get() != NULL:
+            soln._base.get().removeChangedCallback(<PyObject*>(soln))
         soln._base = cxx_soln
     soln.base = cxx_soln.get()
-    soln.thermo = soln.base.thermo().get()
-    soln.kinetics = soln.base.kinetics().get()
-    soln.transport = soln.base.transport().get()
+
+    def assign_pointers():
+        soln.thermo = soln.base.thermo().get()
+        soln.kinetics = soln.base.kinetics().get()
+        soln.transport = soln.base.transport().get()
+    assign_pointers()
+
+    soln.base.registerChangedCallback(<PyObject*>soln,
+        pyOverride(<PyObject*>assign_pointers, callback_v))
+    # PyOverride only holds a weak reference to the function, so this also needs to be
+    # stored on the Python Solution object to have the right lifetime
+    soln._soln_changed_callback = assign_pointers
 
     cdef shared_ptr[CxxSolution] adj_soln
     if reset_adjacent:

interfaces/cython/cantera/transport.pyx

@@ -195,7 +195,6 @@ cdef class Transport(_SolutionBase):
 
         def __set__(self, model):
             self.base.setTransport(newTransport(self.thermo, stringify(model)))
-            self.transport = self.base.transport().get()
 
     property CK_mode:
         """Boolean to indicate if the chemkin interpretation is used."""

src/base/Solution.cpp

@@ -42,6 +42,9 @@ void Solution::setName(const std::string& name) {
 
 void Solution::setThermo(shared_ptr<ThermoPhase> thermo) {
     m_thermo = thermo;
+    for (const auto& [id, callback] : m_changeCallbacks) {
+        callback();
+    }
 }
 
 void Solution::setKinetics(shared_ptr<Kinetics> kinetics) {
@@ -49,10 +52,16 @@ void Solution::setKinetics(shared_ptr<Kinetics> kinetics) {
     if (m_kinetics) {
         m_kinetics->setRoot(shared_from_this());
     }
+    for (const auto& [id, callback] : m_changeCallbacks) {
+        callback();
+    }
 }
 
 void Solution::setTransport(shared_ptr<Transport> transport) {
     m_transport = transport;
+    for (const auto& [id, callback] : m_changeCallbacks) {
+        callback();
+    }
 }
 
 void Solution::setTransportModel(const std::string& model) {
@@ -152,10 +161,20 @@ shared_ptr<ExternalHandle> Solution::getExternalHandle(const std::string& name)
     }
 }
 
-shared_ptr<Solution> newSolution(const std::string& infile,
-                                 const std::string& name,
-                                 const std::string& transport,
-                                 const std::vector<shared_ptr<Solution>>& adjacent)
+void Solution::registerChangedCallback(void *id, const function<void()>& callback)
+{
+    m_changeCallbacks[id] = callback;
+}
+
+void Solution::removeChangedCallback(void* id)
+{
+    m_changeCallbacks.erase(id);
+}
+
+shared_ptr<Solution> newSolution(const std::string &infile,
+                                 const std::string &name,
+                                 const std::string &transport,
+                                 const std::vector<shared_ptr<Solution>> &adjacent)
 {
     // get file extension
     size_t dot = infile.find_last_of(".");

src/oneD/IonFlow.cpp

@@ -64,8 +64,7 @@ IonFlow::IonFlow(shared_ptr<Solution> sol, const std::string& id, size_t points)
     m_solution = sol;
     m_id = id;
     m_kin = m_solution->kinetics().get();
-    m_trans_shared = m_solution->transport();
-    m_trans = m_trans_shared.get();
+    m_trans = m_solution->transport().get();
     if (m_trans->transportModel() == "None") {
         // @deprecated
         warn_deprecated("IonFlow",
@@ -74,6 +73,10 @@ IonFlow::IonFlow(shared_ptr<Solution> sol, const std::string& id, size_t points)
             "is deprecated and\nwill be removed after Cantera 3.0.");
         setTransportModel("Ion");
     }
+    m_solution->registerChangedCallback(this, [this]() {
+        setKinetics(*m_solution->kinetics());
+        setTransport(*m_solution->transport());
+    });
 }
 
 void IonFlow::resize(size_t components, size_t points){

src/oneD/StFlow.cpp

@@ -7,6 +7,7 @@
 #include "cantera/oneD/StFlow.h"
 #include "cantera/oneD/refine.h"
 #include "cantera/transport/Transport.h"
+#include "cantera/transport/TransportFactory.h"
 #include "cantera/numerics/funcs.h"
 #include "cantera/base/global.h"
 
@@ -113,8 +114,7 @@ StFlow::StFlow(shared_ptr<Solution> sol, const std::string& id, size_t points)
     m_solution = sol;
     m_id = id;
     m_kin = m_solution->kinetics().get();
-    m_trans_shared = m_solution->transport();
-    m_trans = m_trans_shared.get();
+    m_trans = m_solution->transport().get();
     if (m_trans->transportModel() == "None") {
         // @deprecated
         warn_deprecated("StFlow",
@@ -123,6 +123,17 @@ StFlow::StFlow(shared_ptr<Solution> sol, const std::string& id, size_t points)
             "is deprecated and\nwill be removed after Cantera 3.0.");
         setTransportModel("Mix");
     }
+    m_solution->registerChangedCallback(this, [this]() {
+        setKinetics(*m_solution->kinetics());
+        setTransport(*m_solution->transport());
+    });
+}
+
+StFlow::~StFlow()
+{
+    if (m_solution) {
+        m_solution->removeChangedCallback(this);
+    }
 }
 
 void StFlow::setThermo(IdealGasPhase& th) {
@@ -187,9 +198,6 @@ void StFlow::setTransportModel(const std::string& trans)
             "from a Solution manager: set Transport object directly instead.");
     }
     m_solution->setTransportModel(trans);
-    m_trans_shared = m_solution->transport();
-    m_trans = m_trans_shared.get();
-    setTransport(*m_trans);
 }
 
 std::string StFlow::transportModel() const {

test/python/test_onedim.py

@@ -128,6 +128,22 @@ class TestOnedim(utilities.CanteraTest):
         self.assertEqual(rtol_ss, set((5e-3, 3e-4, 7e-7)))
         self.assertEqual(rtol_ts, set((6e-3, 4e-4, 2e-7)))
 
+    def test_switch_transport(self):
+        gas = ct.Solution('h2o2.yaml')
+        gas.set_equivalence_ratio(0.9, 'H2', 'O2:0.21, N2:0.79')
+        flame = ct.FreeFlame(gas, width=0.1)
+        flame.set_initial_guess()
+
+        assert gas.transport_model == flame.transport_model == 'Mix'
+
+        flame.transport_model = 'UnityLewis'
+        assert gas.transport_model == flame.transport_model == 'UnityLewis'
+        Dkm_flame = flame.mix_diff_coeffs
+        assert all(Dkm_flame[1,:] == Dkm_flame[2,:])
+
+        gas.transport_model = 'Multi'
+        assert flame.transport_model == 'Multi'
+
 
 class TestFreeFlame(utilities.CanteraTest):
     tol_ss = [1.0e-5, 1.0e-14]  # [rtol atol] for steady-state problem