Carpet: Implement new routine gather_string

2 files changed, 79 insertions, 0 deletions

diff --git a/Carpet/CarpetLib/src/mpi_string.cc b/Carpet/CarpetLib/src/mpi_string.cc
index e0022e3e0..b7e1f9b0e 100644
--- a/Carpet/CarpetLib/src/mpi_string.cc
+++ b/Carpet/CarpetLib/src/mpi_string.cc
@@ -22,6 +22,81 @@ namespace CarpetLib
   
   
   vector <string>
+  gather_string (MPI_Comm const comm,
+                 int const root,
+                 string const & data)
+  {
+    // Get my rank
+    int rank;
+    MPI_Comm_rank (comm, & rank);
+    
+    if (rank == root) {
+      
+      // Get the total number of processors
+      int num_procs;
+      MPI_Comm_size (comm, & num_procs);
+      
+      // Gather the lengths of the data strings
+      int const length = data.length();
+      vector <int> lengths (num_procs);
+      
+      MPI_Gather (const_cast <int *> (& length), 1, MPI_INT,
+                  & lengths.front(), 1, MPI_INT,
+                  root, comm);
+      
+      // Allocate space for all data strings
+      vector <int> offsets (num_procs + 1);
+      offsets.AT(0) = 0;
+      for (int n = 0; n < num_procs; ++ n)
+      {
+        offsets.AT(n + 1) = offsets.AT(n) + lengths.AT(n);
+      }
+      int const total_length = offsets.AT(num_procs);
+      vector <char> alldata_buffer (total_length);
+      
+      // Gather all data strings
+      MPI_Gatherv (const_cast <char *> (data.c_str()), length, MPI_CHAR,
+                   & alldata_buffer.front(),
+                   const_cast <int *> (& lengths.front()),
+                   const_cast <int *> (& offsets.front()),
+                   MPI_CHAR,
+                   root, comm);
+      
+      // Convert data buffer with C strings to C++ strings
+      vector <string> alldata  (num_procs);
+      for (int n = 0; n < num_procs; ++ n)
+      {
+        alldata.AT(n) =
+          string (& alldata_buffer.AT (offsets.AT(n)), lengths.AT(n));
+      }
+      
+      return alldata;
+      
+    } else {
+      
+      // Gather the lengths of the data strings
+      int const length = data.length();
+      
+      MPI_Gather (const_cast <int *> (& length), 1, MPI_INT,
+                  NULL, 1, MPI_INT,
+                  root, comm);
+      
+      // Gather all data strings
+      MPI_Gatherv (const_cast <char *> (data.c_str()), length, MPI_CHAR,
+                   NULL, NULL, NULL, MPI_CHAR,
+                   root, comm);
+      
+      // Convert data buffer with C strings to C++ strings
+      vector <string> alldata;
+      
+      return alldata;
+      
+    }
+  }
+  
+  
+  
+  vector <string>
   allgather_string (MPI_Comm const comm,
                     string const & data)
   {
diff --git a/Carpet/CarpetLib/src/mpi_string.hh b/Carpet/CarpetLib/src/mpi_string.hh
index 6ed8d447d..f05910139 100644
--- a/Carpet/CarpetLib/src/mpi_string.hh
+++ b/Carpet/CarpetLib/src/mpi_string.hh
@@ -17,6 +17,10 @@ namespace CarpetLib
   // String communication
   
   vector <string>
+  gather_string (MPI_Comm comm, int root,
+                 string const & data);
+  
+  vector <string>
   allgather_string (MPI_Comm comm,
                     string const & data);