Obtain the replicas communicator from GROMACS

Simplified version of the code in Colvars/gromacs#4

Patch core GROMACS files

gromacs/gromacs-mdmodules.patch

@@ -0,0 +1,32 @@
+diff --git a/src/gromacs/mdrun/runner.cpp b/src/gromacs/mdrun/runner.cpp
+index 321833a6d6..e847921390 100644
+--- a/src/gromacs/mdrun/runner.cpp
++++ b/src/gromacs/mdrun/runner.cpp
+@@ -1837,6 +1837,7 @@ int Mdrunner::mdrunner()
+     if (thisRankHasDuty(cr, DUTY_PP))
+     {
+         setupNotifier.notify(*cr);
++        setupNotifier.notify(ms);
+         setupNotifier.notify(&atomSets);
+         setupNotifier.notify(mtop);
+         setupNotifier.notify(inputrec->pbcType);
+diff --git a/src/gromacs/mdrunutility/mdmodulesnotifiers.h b/src/gromacs/mdrunutility/mdmodulesnotifiers.h
+index 913cb0b3c4..76c8ebc09a 100644
+--- a/src/gromacs/mdrunutility/mdmodulesnotifiers.h
++++ b/src/gromacs/mdrunutility/mdmodulesnotifiers.h
+@@ -62,6 +62,7 @@ struct gmx_mtop_t;
+ class WarningHandler;
+ enum class PbcType : int;
+ struct t_inputrec;
++struct gmx_multisim_t;
+
+ namespace gmx
+ {
+@@ -395,6 +396,7 @@ struct MDModulesNotifiers
+                            const SimulationTimeStep&,
+                            const EnsembleTemperature&,
+                            const t_commrec&,
++                           const gmx_multisim_t*,
+                            const MdRunInputFilename&,
+                            const EdrOutputFilename&,
+                            const PlumedInputFilename&>::type simulationSetupNotifier_;

gromacs/gromacs-mdmodules/applied_forces/colvars/colvarsMDModule.cpp

@@ -40,15 +40,14 @@
  */
 #include "gmxpre.h"
 
-#include "colvarsMDModule.h"
-
 #include <functional>
 #include <memory>
 #include <string>
 
 #include "gromacs/domdec/localatomsetmanager.h"
 #include "gromacs/fileio/checkpoint.h"
 #include "gromacs/mdrunutility/mdmodulesnotifiers.h"
+#include "gromacs/mdrunutility/multisim.h"
 #include "gromacs/mdtypes/commrec.h"
 #include "gromacs/mdtypes/iforceprovider.h"
 #include "gromacs/mdtypes/imdmodule.h"
@@ -58,6 +57,8 @@
 #include "colvarsoptions.h"
 #include "colvarssimulationsparameters.h"
 
+#include "colvarsMDModule.h"
+
 enum class PbcType : int;
 struct gmx_mtop_t;
 
@@ -97,7 +98,7 @@ class ColvarsMDModule final : public IMDModule
      *     KeyValueTreeObjectBuilder as parameter
      *   - Acess topology using gmx_mtop_t notification
      *   - Access MDLogger for notifications output
-     *   - Access warninp for for grompp warnings output
+     *   - Access warning for for grompp warnings output
      *   - Coordinates, PBC and box for setting up the proxy
      */
     void subscribeToPreProcessingNotifications(MDModulesNotifiers* notifier) override
@@ -192,6 +193,12 @@ class ColvarsMDModule final : public IMDModule
         };
         notifier->simulationSetupNotifier_.subscribe(setCommFunction);
 
+        // Retrieve the Multisim Record during simulations setup
+        const auto setMultisimFunction = [this](const gmx_multisim_t *ms) {
+            this->ColvarsSimulationsParameters_.setMultisim(ms);
+        };
+        notifier->simulationSetupNotifier_.subscribe(setMultisimFunction);
+
         // setting the simulation time step
         const auto setSimulationTimeStepFunction = [this](const SimulationTimeStep& simulationTimeStep) {
             this->ColvarsSimulationsParameters_.setSimulationTimeStep(simulationTimeStep.delta_t);
@@ -251,6 +258,7 @@ class ColvarsMDModule final : public IMDModule
                     colvarsOptions_.colvarsSeed(),
                     ColvarsSimulationsParameters_.localAtomSetManager(),
                     ColvarsSimulationsParameters_.comm(),
+                    ColvarsSimulationsParameters_.ms(),
                     ColvarsSimulationsParameters_.simulationTimeStep(),
                     colvarsOptions_.colvarsAtomCoords(),
                     colvarsOptions_.colvarsOutputPrefix(),

gromacs/gromacs-mdmodules/applied_forces/colvars/colvarsforceprovider.cpp

@@ -39,16 +39,12 @@
  * \ingroup module_applied_forces
  */
 
-#include "colvarsforceprovider.h"
-
 #include <cstddef>
 #include <cstdint>
 
 #include <array>
 #include <string>
 
-#include "external/colvars/colvars_memstream.h"
-
 #include "gromacs/applied_forces/colvars/colvarproxygromacs.h"
 #include "gromacs/compat/pointers.h"
 #include "gromacs/domdec/localatomsetmanager.h"
@@ -57,6 +53,7 @@
 #include "gromacs/math/vec.h"
 #include "gromacs/mdlib/broadcaststructs.h"
 #include "gromacs/mdlib/groupcoord.h"
+#include "gromacs/mdrunutility/multisim.h"
 #include "gromacs/mdtypes/commrec.h"
 #include "gromacs/mdtypes/enerdata.h"
 #include "gromacs/mdtypes/forceoutput.h"
@@ -65,10 +62,15 @@
 #include "gromacs/utility/arrayref.h"
 #include "gromacs/utility/basedefinitions.h"
 #include "gromacs/utility/exceptions.h"
+#include "gromacs/utility/gmxmpi.h"
 #include "gromacs/utility/keyvaluetree.h"
 #include "gromacs/utility/keyvaluetreebuilder.h"
 #include "gromacs/utility/smalloc.h"
 
+#include "colvarsforceprovider.h"
+
+#include "external/colvars/colvars_memstream.h"
+
 enum class PbcType : int;
 
 
@@ -173,6 +175,7 @@ ColvarsForceProvider::ColvarsForceProvider(const std::string& colvarsConfigStrin
                                            int                              seed,
                                            LocalAtomSetManager*             localAtomSetManager,
                                            const t_commrec*                 cr,
+                                           const gmx_multisim_t*            ms,
                                            double                           simulationTimeStep,
                                            const std::vector<RVec>&         colvarsCoords,
                                            const std::string&               outputPrefix,
@@ -236,6 +239,14 @@ ColvarsForceProvider::ColvarsForceProvider(const std::string& colvarsConfigStrin
     snew(fColvars, nColvarsAtoms);
     snew(xColvarsOldWhole, nColvarsAtoms);
 
+#if GMX_MPI
+    if (MAIN(cr))
+    {
+        if (isMultiSim(ms)) {
+            colvarproxy::set_replicas_mpi_communicator(ms->mainRanksComm_);
+        }
+    }
+#endif
 
     // Check state status (did we read a cpt file?)
     if (MAIN(cr))

gromacs/gromacs-mdmodules/applied_forces/colvars/colvarsforceprovider.h

@@ -61,6 +61,7 @@
 
 enum class PbcType : int;
 struct t_commrec;
+struct gmx_multisim_t;
 
 
 namespace gmx
@@ -196,6 +197,7 @@ class ColvarsForceProvider final : public ColvarProxyGromacs, public IForceProvi
                          int                                       seed,
                          LocalAtomSetManager*                      localAtomSetManager,
                          const t_commrec*                          cr,
+                         const gmx_multisim_t*                     ms,
                          double                                    simulationTimeStep,
                          const std::vector<RVec>&                  colvarsCoords,
                          const std::string&                        outputPrefix,

gromacs/gromacs-mdmodules/applied_forces/colvars/colvarssimulationsparameters.cpp

@@ -114,6 +114,16 @@ const t_commrec* ColvarsSimulationsParameters::comm() const
     return cr_;
 }
 
+void ColvarsSimulationsParameters::setMultisim(const gmx_multisim_t *ms)
+{
+    ms_ = ms;
+}
+
+const gmx_multisim_t* ColvarsSimulationsParameters::ms() const
+{
+    return ms_;
+}
+
 
 void ColvarsSimulationsParameters::setLogger(const MDLogger& logger)
 {

gromacs/gromacs-mdmodules/applied_forces/colvars/colvarssimulationsparameters.h

@@ -50,6 +50,7 @@
 #include "gromacs/pbcutil/pbc.h"
 #include "gromacs/topology/atoms.h"
 #include "gromacs/utility/logger.h"
+struct gmx_multisim_t;
 
 struct gmx_mtop_t;
 
@@ -109,7 +110,12 @@ class ColvarsSimulationsParameters
     //! Return the communicator
     const t_commrec* comm() const;
 
-    /*! \brief Set the logger for QMMM during mdrun
+    //! Set the Multisim record
+    void setMultisim(const gmx_multisim_t *ms);
+    //! Return Multisim record
+    const gmx_multisim_t* ms() const;
+
+    /*! \brief Set the logger for Colvars during mdrun
      * \param[in] logger Logger instance to be used for output
      */
     void setLogger(const MDLogger& logger);
@@ -128,6 +134,8 @@ class ColvarsSimulationsParameters
     t_atoms gmxAtoms_;
     //! The communicator
     const t_commrec* cr_;
+    //! The multisim record
+    const gmx_multisim_t *ms_;
     //! MDLogger for notifications during mdrun
     const MDLogger* logger_ = nullptr;