Plotting

All plotting in Peano is typically realised through the files in tarch/plotter.

The idea is that you have an action set which dumps the data. To do so, it owns a plotter class. This implies that each tree in the system owns its own plotter and writes (logically) into its own output file. The plotter under the hood might do something clever with merging those guys, but logically it is a one file per action set approach.

Action set pattern

You never know how much meta data plotter object holds and when this data is dumped into the file. Therefore, most action sets which dump data allocate the plotter object on the heap within beginTraversal(). They delete this object in endTraversal(), which is the latest point when the plotter will actually stream its data into a file.

Parallel plotting

Most plotters either are shipped with a dedicated index file class which you can wrap around the actual plotter, or they provide a constructor which can coordinate an action set's plotting with all the other plotting that's going on in parallel. For the Peano mesh format plotter, the constructor looks similar to

_writer = new tarch::plotter::griddata::blockstructured::PeanoTextPatchFileWriter(
  DIMENSIONS, snapshotFileName.str(), "grid",
  tarch::plotter::griddata::blockstructured::PeanoTextPatchFileWriter::IndexFileMode::AppendNewData,
  repositories::getMinTimeStamp()
);    

and the AppendNewData flag indicates that the code should look up the index file "grid.file-format-specific-extension" and add a new snapshot called snapshotFileName.str() to it.

Before we discuss how we implement this constructor, let's clarify that this constructor is neither thread-safe nor MPI-safe. That is, you should not call it concurrently from two threads or two ranks. To ensure that this does not happen, you typically wrap the construction into a tarch::mpi::Lock region around an global instance of tarch::mpi::BooleanSemaphore.

A comprehensive (and documented) version of such a plotter is tarch::plotter::griddata::blockstructured::PeanoTextPatchFileWriter.