VTXWriter: support file modes

cpp/demo/interpolation-io/main.cpp

@@ -66,8 +66,8 @@ void interpolate_scalar(std::shared_ptr<mesh::Mesh<U>> mesh,
 #ifdef HAS_ADIOS2
   // Write the function to a VTX file for visualisation, e.g. using
   // ParaView
-  io::VTXWriter<U> outfile(mesh->comm(), filename.replace_extension("bp"), {u},
-                           "BP4");
+  io::VTXWriter<U> outfile(mesh->comm(), filename.replace_extension("bp"), "w",
+                           {u}, "BP4");
   outfile.write(0);
   outfile.close();
 #endif
@@ -183,7 +183,7 @@ void interpolate_nedelec(std::shared_ptr<mesh::Mesh<U>> mesh,
 // (jump in the normal component between cells) and the x1 component
 // will appear continuous (continuous tangent component between cells).
 #ifdef HAS_ADIOS2
-  io::VTXWriter<U> outfile(mesh->comm(), filename.replace_extension("bp"),
+  io::VTXWriter<U> outfile(mesh->comm(), filename.replace_extension("bp"), "w",
                            {u_l}, "BP4");
   outfile.write(0);
   outfile.close();

cpp/demo/interpolation_different_meshes/main.cpp

@@ -86,9 +86,9 @@ int main(int argc, char* argv[])
     u_hex->interpolate(*u_tet, cells, eps, max_iter, interpolation_data);
 
 #ifdef HAS_ADIOS2
-    io::VTXWriter<double> write_tet(mesh_tet->comm(), "u_tet.bp", {u_tet});
+    io::VTXWriter<double> write_tet(mesh_tet->comm(), "u_tet.bp", "w", {u_tet});
     write_tet.write(0);
-    io::VTXWriter<double> write_hex(mesh_hex->comm(), "u_hex.bp", {u_hex});
+    io::VTXWriter<double> write_hex(mesh_hex->comm(), "u_hex.bp", "w", {u_hex});
     write_hex.write(0);
 #endif
   }

cpp/demo/mixed_poisson/main.cpp

@@ -364,10 +364,10 @@ int main(int argc, char* argv[])
 
 #ifdef HAS_ADIOS2
     // Save solution in VTX format
-    io::VTXWriter<U> vtx_u(MPI_COMM_WORLD, "u.bp", {u_soln}, "bp4");
+    io::VTXWriter<U> vtx_u(MPI_COMM_WORLD, "u.bp", "w", {u_soln}, "bp4");
     vtx_u.write(0);
     // Save interpolated boundary condition
-    io::VTXWriter<U> vtx_u0(MPI_COMM_WORLD, "u0.bp", {u0}, "bp4");
+    io::VTXWriter<U> vtx_u0(MPI_COMM_WORLD, "u0.bp", "w", {u0}, "bp4");
     vtx_u0.write(0);
 #endif
   }

cpp/demo/poisson/main.cpp

@@ -250,7 +250,7 @@ int main(int argc, char* argv[])
 
 #ifdef HAS_ADIOS2
     // Save solution in VTX format
-    io::VTXWriter<U> vtx(MPI_COMM_WORLD, "u.bp", {u}, "bp4");
+    io::VTXWriter<U> vtx(MPI_COMM_WORLD, "u.bp", "w", {u}, "bp4");
     vtx.write(0);
 #endif
   }

cpp/dolfinx/io/ADIOS2Writers.cpp

@@ -18,13 +18,13 @@
 
 //-----------------------------------------------------------------------------
 ADIOS2Writer::ADIOS2Writer(MPI_Comm comm, const std::filesystem::path& filename,
-                           std::string tag, std::string engine)
+                           adios2::Mode mode, std::string tag,
+                           std::string engine)
     : _adios(std::make_unique<adios2::ADIOS>(comm)),
       _io(std::make_unique<adios2::IO>(_adios->DeclareIO(std::move(tag))))
 {
   _io->SetEngine(std::move(engine));
-  _engine = std::make_unique<adios2::Engine>(
-      _io->Open(filename, adios2::Mode::Write));
+  _engine = std::make_unique<adios2::Engine>(_io->Open(filename, mode));
 }
 //-----------------------------------------------------------------------------
 ADIOS2Writer::~ADIOS2Writer() { close(); }
@@ -38,6 +38,24 @@
     _engine->Close();
 }
 //-----------------------------------------------------------------------------
+adios2::Mode impl_adios2::mode(std::string_view mode)
+{
+  if (mode == "a")
+    return adios2::Mode::Append;
+
+  if (mode == "w")
+    return adios2::Mode::Write;
+
+  // unsupported adios2 modes:
+  // - Undefined
+  // - Read
+  // - ReadRandomAccess
+  // - Sync
+  // - Deferred
+
+  throw std::runtime_error("Invalid adios2 mode.");
+}
+//-----------------------------------------------------------------------------
 std::stringstream
 io::impl_vtx::create_vtk_schema(const std::vector<std::string>& point_data,
                                 const std::vector<std::string>& cell_data)

cpp/dolfinx/io/ADIOS2Writers.h

@@ -6,10 +6,12 @@
 
 #pragma once
 
+#include <string_view>
 #ifdef HAS_ADIOS2
 
 #include "vtk_utils.h"
 #include <adios2.h>
+#include <adios2/common/ADIOSTypes.h>
 #include <algorithm>
 #include <basix/mdspan.hpp>
 #include <cassert>
@@ -59,11 +61,12 @@ class ADIOS2Writer
   /// @brief Create an ADIOS2-based writer
   /// @param[in] comm The MPI communicator
   /// @param[in] filename Name of output file
+  /// @param[in] mode Mode to open file with
   /// @param[in] tag The ADIOS2 object name
   /// @param[in] engine ADIOS2 engine type. See
   /// https://adios2.readthedocs.io/en/latest/engines/engines.html.
   ADIOS2Writer(MPI_Comm comm, const std::filesystem::path& filename,
-               std::string tag, std::string engine);
+               adios2::Mode mode, std::string tag, std::string engine);
 
   /// @brief Move constructor
   ADIOS2Writer(ADIOS2Writer&& writer) = default;
@@ -157,6 +160,11 @@ extract_common_mesh(const typename adios2_writer::U<T>& u)
   return mesh;
 }
 
+/// Convert string to corresponding adios2 mode.
+/// @param[in] mode Mode in string representation, either "w" or "a".
+/// @returns Adios2 mode.
+adios2::Mode mode(std::string_view mode);
+
 } // namespace impl_adios2
 
 /// @privatesection
@@ -461,16 +469,18 @@ class VTXWriter : public ADIOS2Writer
   ///
   /// @param[in] comm MPI communicator to open the file on.
   /// @param[in] filename Name of output file.
+  /// @param[in] mode Mode to open file with
   /// @param[in] mesh Mesh to write.
   /// @param[in] engine ADIOS2 engine type.
   /// @note This format supports arbitrary degree meshes.
   /// @note The mesh geometry can be updated between write steps but the
   /// topology should not be changed between write steps.
   VTXWriter(MPI_Comm comm, const std::filesystem::path& filename,
-            std::shared_ptr<const mesh::Mesh<T>> mesh,
+            const std::string& mode, std::shared_ptr<const mesh::Mesh<T>> mesh,
             std::string engine = "BPFile")
-      : ADIOS2Writer(comm, filename, "VTX mesh writer", engine), _mesh(mesh),
-        _mesh_reuse_policy(VTXMeshPolicy::update),
+      : ADIOS2Writer(comm, filename, impl_adios2::mode(mode), "VTX mesh writer",
+                     engine),
+        _mesh(mesh), _mesh_reuse_policy(VTXMeshPolicy::update),
         _has_piecewise_constant(false)
   {
     // Define VTK scheme attribute for mesh
@@ -484,6 +494,7 @@ class VTXWriter : public ADIOS2Writer
   ///
   /// @param[in] comm The MPI communicator to open the file on
   /// @param[in] filename Name of output file
+  /// @param[in] mode Mode to open file with
   /// @param[in] u List of functions. The functions must (1) share the
   /// same mesh and (2) be (discontinuous) Lagrange functions. The
   /// element family and degree, and degree-of-freedom map (up to the
@@ -494,9 +505,11 @@ class VTXWriter : public ADIOS2Writer
   /// step.
   /// @note This format supports arbitrary degree meshes.
   VTXWriter(MPI_Comm comm, const std::filesystem::path& filename,
-            const typename adios2_writer::U<T>& u, std::string engine,
+            const std::string& mode, const typename adios2_writer::U<T>& u,
+            std::string engine,
             VTXMeshPolicy mesh_policy = VTXMeshPolicy::update)
-      : ADIOS2Writer(comm, filename, "VTX function writer", engine),
+      : ADIOS2Writer(comm, filename, impl_adios2::mode(mode),
+                     "VTX function writer", engine),
         _mesh(impl_adios2::extract_common_mesh<T>(u)), _u(u),
         _mesh_reuse_policy(mesh_policy), _has_piecewise_constant(false)
   {
@@ -595,6 +608,7 @@ class VTXWriter : public ADIOS2Writer
   ///
   /// @param[in] comm The MPI communicator to open the file on
   /// @param[in] filename Name of output file
+  /// @param[in] mode Mode to open file with
   /// @param[in] u List of functions. The functions must (1) share the
   /// same mesh and (2) be (discontinuous) Lagrange functions. The
   /// element family and degree must be the same for all functions.
@@ -603,9 +617,9 @@ class VTXWriter : public ADIOS2Writer
   /// step.
   /// @note This format supports arbitrary degree meshes.
   VTXWriter(MPI_Comm comm, const std::filesystem::path& filename,
-            const typename adios2_writer::U<T>& u,
+            const std::string& mode, const typename adios2_writer::U<T>& u,
             VTXMeshPolicy mesh_policy = VTXMeshPolicy::update)
-      : VTXWriter(comm, filename, u, "BPFile", mesh_policy)
+      : VTXWriter(comm, filename, mode, u, "BPFile", mesh_policy)
   {
   }
 

cpp/test/io.cpp

@@ -45,7 +45,7 @@ void test_vtx_reuse_mesh()
 
   std::filesystem::path f
       = "test_vtx_reuse_mesh" + std::to_string(sizeof(T)) + ".bp";
-  io::VTXWriter<T> writer(mesh->comm(), f, {u, v}, "BPFile",
+  io::VTXWriter<T> writer(mesh->comm(), f, "w", {u, v}, "BPFile",
                           io::VTXMeshPolicy::reuse);
   writer.write(0);
 

python/demo/demo_axis.py

@@ -794,6 +794,6 @@ def create_eps_mu(pml, rho, eps_bkg, mu_bkg):
     Es_dg = fem.Function(W)
     Es_expr = fem.Expression(Esh, W.element.interpolation_points)
     Es_dg.interpolate(Es_expr)
-    with VTXWriter(mesh_data.mesh.comm, out_folder / "Es.bp", Es_dg) as f:
+    with VTXWriter(mesh_data.mesh.comm, out_folder / "Es.bp", "w", Es_dg) as f:
         f.write(0.0)
 # -

python/demo/demo_biharmonic.py

@@ -330,7 +330,7 @@
 if has_adios2:
     out_folder = Path("out_biharmonic")
     out_folder.mkdir(parents=True, exist_ok=True)
-    with io.VTXWriter(msh.comm, out_folder / "biharmonic.bp", [uh]) as file:
+    with io.VTXWriter(msh.comm, out_folder / "biharmonic.bp", "w", [uh]) as file:
         file.write(0.0)
 
 # and displayed using [pyvista](https://docs.pyvista.org/).

python/demo/demo_half_loaded_waveguide.py

@@ -469,10 +469,10 @@ def verify_mode(
 
         if has_vtx:
             # Save solutions
-            with VTXWriter(msh.comm, out_folder / f"Et_{i}.bp", Et_dg) as f:
+            with VTXWriter(msh.comm, out_folder / f"Et_{i}.bp", "w", Et_dg) as f:
                 f.write(0.0)
 
-            with VTXWriter(msh.comm, out_folder / f"Ez_{i}.bp", ezh) as f:
+            with VTXWriter(msh.comm, out_folder / f"Ez_{i}.bp", "w", ezh) as f:
                 f.write(0.0)
 
         # Visualize solutions with Pyvista

python/demo/demo_hdg.py

@@ -264,9 +264,9 @@ def u_e(x):
 if dolfinx.has_adios2:
     from dolfinx.io import VTXWriter
 
-    with VTXWriter(msh.comm, "u.bp", u, "bp4") as f:
+    with VTXWriter(msh.comm, "u.bp", "w", u, "bp4") as f:
         f.write(0.0)
-    with VTXWriter(msh.comm, "ubar.bp", ubar, "bp4") as f:
+    with VTXWriter(msh.comm, "ubar.bp", "w", ubar, "bp4") as f:
         f.write(0.0)
 else:
     print("ADIOS2 required for VTX output")

python/demo/demo_interpolation-io.py

@@ -82,7 +82,7 @@
 if has_adios2:
     from dolfinx.io import VTXWriter
 
-    with VTXWriter(msh.comm, out_folder / "output_nedelec.bp", u0) as f:
+    with VTXWriter(msh.comm, out_folder / "output_nedelec.bp", "w", u0) as f:
         f.write(0.0)
 else:
     print("ADIOS2 required for VTX output")

python/demo/demo_mixed-poisson.py

@@ -352,7 +352,7 @@
 if dolfinx.has_adios2:
     from dolfinx.io import VTXWriter
 
-    with VTXWriter(msh.comm, "output_mixed_poisson.bp", u) as f:
+    with VTXWriter(msh.comm, "output_mixed_poisson.bp", "w", u) as f:
         f.write(0.0)
 else:
     print("ADIOS2 required for VTX output.")

python/demo/demo_navier-stokes.py

@@ -367,10 +367,10 @@ def jump(phi, n):
 if has_adios2:
     u_vis = fem.Function(W, name="u_init")
     u_vis.interpolate(u_h)
-    u_file = io.VTXWriter(msh.comm, "u.bp", u_vis)
-    p_file = io.VTXWriter(msh.comm, "p.bp", p_h)
-    u_file.write(t)
-    p_file.write(t)
+    with io.VTXWriter(msh.comm, "u.bp", "w", u_vis) as file:
+        file.write(t)
+    with io.VTXWriter(msh.comm, "p.bp", "w", p_h) as file:
+        file.write(t)
 else:
     print("File output requires ADIOS2.")
 
@@ -422,17 +422,13 @@ def jump(phi, n):
     # Write to file
     if has_adios2:
         u_vis.interpolate(u_h)
-        u_file.write(t)
-        p_file.write(t)
+        with io.VTXWriter(msh.comm, "u.bp", "a", u_vis) as file:
+            file.write(t)
+        with io.VTXWriter(msh.comm, "p.bp", "a", u_vis) as file:
+            file.write(t)
 
     # Update u_n
     u_n.x.array[:] = u_h.x.array
-
-try:
-    u_file.close()
-    p_file.close()
-except NameError:
-    pass
 # -
 
 # Now we compare the computed solution to the exact solution

python/demo/demo_pml.py

@@ -666,7 +666,7 @@ def create_eps_mu(
 Esh_dg = fem.Function(V_dg)
 Esh_dg.interpolate(Esh)
 
-with VTXWriter(mesh_data.mesh.comm, out_folder / "Esh.bp", Esh_dg) as vtx:
+with VTXWriter(mesh_data.mesh.comm, out_folder / "Esh.bp", "w", Esh_dg) as vtx:
     vtx.write(0.0)
 # -
 
@@ -702,7 +702,7 @@ def create_eps_mu(
 E_dg = fem.Function(V_dg)
 E_dg.interpolate(E)
 
-with VTXWriter(mesh_data.mesh.comm, out_folder / "E.bp", E_dg) as vtx:
+with VTXWriter(mesh_data.mesh.comm, out_folder / "E.bp", "w", E_dg) as vtx:
     vtx.write(0.0)
 # -
 

python/demo/demo_scattering_boundary_conditions.py

@@ -655,7 +655,7 @@ def curl_2d(f: fem.Function):
 assert isinstance(Esh, fem.Function)
 Esh_dg.interpolate(Esh)
 
-with io.VTXWriter(mesh_data.mesh.comm, out_folder / "Esh.bp", Esh_dg) as vtx:
+with io.VTXWriter(mesh_data.mesh.comm, out_folder / "Esh.bp", "w", Esh_dg) as vtx:
     vtx.write(0.0)
 # -
 
@@ -694,7 +694,7 @@ def curl_2d(f: fem.Function):
 E.x.array[:] = Eb.x.array[:] + Esh.x.array[:]
 E_dg = fem.Function(V_dg)
 E_dg.interpolate(E)
-with io.VTXWriter(mesh_data.mesh.comm, "E.bp", E_dg) as vtx:
+with io.VTXWriter(mesh_data.mesh.comm, "E.bp", "w", E_dg) as vtx:
     vtx.write(0.0)
 # -
 

python/dolfinx/io/utils.py

@@ -47,6 +47,7 @@ def __init__(
             self,
             comm: _MPI.Comm,
             filename: str | Path,
+            mode: str,
             output: Mesh | Function | list[Function] | tuple[Function],
             engine: str = "BPFile",
             mesh_policy: VTXMeshPolicy = VTXMeshPolicy.update,
@@ -56,6 +57,8 @@ def __init__(
             Args:
                 comm: The MPI communicator
                 filename: The output filename
+                mode: The filemode to open the file in, 'a' (append) or 'w'
+                    (write).
                 output: The data to output. Either a mesh, a single
                     (discontinuous) Lagrange Function or list of
                     (discontinuous) Lagrange Functions.
@@ -87,14 +90,16 @@ def __init__(
                 raise RuntimeError(f"VTXWriter does not support dtype={dtype}.")
 
             if isinstance(output, Mesh):
-                self._cpp_object = _vtxwriter(comm, filename, output._cpp_object, engine)  # type: ignore[union-attr]
+                self._cpp_object = _vtxwriter(comm, filename, mode, output._cpp_object, engine)  # type: ignore[union-attr]
             else:
                 cpp_objects = (
                     [output._cpp_object]
                     if isinstance(output, Function)
                     else [o._cpp_object for o in output]
                 )
-                self._cpp_object = _vtxwriter(comm, filename, cpp_objects, engine, mesh_policy)
+                self._cpp_object = _vtxwriter(
+                    comm, filename, mode, cpp_objects, engine, mesh_policy
+                )
 
         def __enter__(self):
             """Enter context manager."""