Add support for "user" output

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## Current develop
 
 ### Added (new features/APIs/variables/...)
+- [[PR 1362]](https://github.com/parthenon-hpc-lab/parthenon/pull/1362) Add support for completely custom "user" output
 
 
 ### Changed (changing behavior/API/variables/...)

doc/sphinx/src/outputs.rst

@@ -406,6 +406,32 @@ The following is a minimal example to plot a 1D and 2D histogram from the output
       plt.pcolormesh(x,y,z,)
       plt.show()
 
+User
+----
+
+Parthenon provides a simple callback for downstream codes to enroll their own
+output routines.
+In the input file, include a ``<parthenon/output*>`` block and specify
+``file_type = user``.
+Output frequency is controlld via ``dt`` or ``dn`` as for other output types.
+Using this callback requires a downstream code to implement the
+``UserOutput::WriteOutputFile`` (required) and  ``UserOutput::GenerateFilename_``
+(optional, but recommended given the structure of the other output types)
+functions.
+
+.. code:: c++
+
+   class UserOutput : public OutputType {
+     public:
+       explicit UserOutput(const OutputParameters &oparams) : OutputType(oparams) {}
+       void WriteOutputFile(Mesh *pm, ParameterInput *pin, SimTime *tm,
+                            const SignalHandler::OutputSignal signal) override;
+     private:
+      std::string GenerateFilename_(ParameterInput *pin, SimTime *tm,
+                                    const SignalHandler::OutputSignal signal);
+   };
+
+
 Ascent (optional)
 -----------------
 

src/outputs/outputs.cpp

@@ -298,7 +298,7 @@ Outputs::Outputs(Mesh *pm, ParameterInput *pin, SimTime *tm) {
     // set output variable and optional data format string used in formatted writes
     if ((op.file_type != "hst") && (op.file_type != "rst") &&
         (op.file_type != "corehdf5") && (op.file_type != "ascent") &&
-        (op.file_type != "histogram")) {
+        (op.file_type != "histogram") && op.file_type != "user") {
       // Do not use GetOrAddVector because it will pollute the input parameters for
       // restarts
       if (pin->DoesParameterExist(op.block_name, "variables")) {
@@ -365,6 +365,8 @@ Outputs::Outputs(Mesh *pm, ParameterInput *pin, SimTime *tm) {
           << std::endl;
       PARTHENON_FAIL(msg);
 #endif // ifdef ENABLE_HDF5
+    } else if (op.file_type == "user") {
+      pnew_type = std::make_shared<UserOutput>(op);
     } else if (is_hdf5_output) {
       restart = (op.file_type == "rst");
       const bool coredump = (op.file_type == "corehdf5");

src/outputs/outputs.hpp

@@ -242,6 +242,21 @@ class HistogramOutput : public OutputType {
 };
 #endif // ifdef ENABLE_HDF5
 
+//----------------------------------------------------------------------------------------
+//! \class UserOutput
+//  \brief derived OutputType class for User enrolled outputs
+
+class UserOutput : public OutputType {
+ public:
+  explicit UserOutput(const OutputParameters &oparams) : OutputType(oparams) {}
+  void WriteOutputFile(Mesh *pm, ParameterInput *pin, SimTime *tm,
+                       const SignalHandler::OutputSignal signal) override;
+
+ private:
+  std::string GenerateFilename_(ParameterInput *pin, SimTime *tm,
+                                const SignalHandler::OutputSignal signal);
+};
+
 //----------------------------------------------------------------------------------------
 //! \class Outputs