change proc count to color for MPI_Comm_split

doc/src/Section_start.txt

@@ -1352,24 +1352,27 @@ specified file is "none", then no log files are created.  Using a
 "log"_log.html command in the input script will override this setting.
 Option -plog will override the name of the partition log files file.N.
 
--mpi P :pre
+-mpi color :pre
 
 If used, this must be the first command-line argument after the LAMMPS
-executable name.  It is only used when running LAMMPS in client/server
+executable name.  It is only used when LAMMPS is launched by an mpirun
-mode with the "mpi/one" mode of messaging provided by the
+command which also launches another executable(s) (the other
-"message"_message.html command and the CSlib library LAMMPS links with
+executable could be LAMMPS as well) at the same time.  The color is an
-from the lib/message directory.  See the "message"_message.html
+integer value which should be different for each executable (another
-command for more details
+application may set this value in a different way).  LAMMPS and the
-
+other executable(s) perform an MPI_Comm_split() with their own colors
-In the mpi/one mode of messaging, both executables (the client and the
+to shrink the MPI_COMM_WORLD communication to be the subset of
-server) are launched by one mpirun command.  P should be specified as
-the number of processors (MPI tasks) the first executable is running
-on (could be the client or the server code).
-
-This information is required so that both codes can shrink the
-MPI_COMM_WORLD communicator they are part of to the subset of
 processors they are actually running on.
 
+Currently, this is only used in LAMMPS to perform client/server
+messaging with another application.  LAMMPS can act as either a client
+or server (or both).
+
+Specifically, this refers to the "mpi/one" mode of messaging provided
+by the "message"_message.html command and the CSlib library LAMMPS
+links with from the lib/message directory.  See the
+"message"_message.html command for more details.
+
 -nocite :pre
 
 Disable writing the log.cite file which is normally written to list

examples/message/README

@@ -91,12 +91,11 @@ Mpi/one mode of messaging:
 
 Launch LAMMPS twice in a single mpirun command:
 
-mpirun -np 2 lmp_mpi -mpi 2 -in in.message.client -v mode mpione -log log.client : -np 4 lmp_mpi -mpi 2 -in in.message.server -v mode mpione -log log.server
+mpirun -np 2 lmp_mpi -mpi 0 -in in.message.client -v mode mpione -log log.client : -np 4 lmp_mpi -mpi 1 -in in.message.server -v mode mpione -log log.server
 
 The two -np values determine how many procs the client and the server
 run on.
 
-A LAMMPS executable run in this manner must use the -mpi P
+A LAMMPS executable run in this manner must use the -mpi color
-command-line option as their first option, where P is the number of
+command-line option as their first option, where color is set to
-processors the first code in the mpirun command (client or server) is
+one integer value for the 1st app, and another value for the 2nd app.
-running on.

src/lammps.cpp

@@ -86,17 +86,17 @@ LAMMPS::LAMMPS(int narg, char **arg, MPI_Comm communicator)
   // check if -mpi is first arg
   // if so, then 2 apps were launched with one mpirun command
   //   this means passed communicator (e.g. MPI_COMM_WORLD) is bigger than LAMMPS
-  //   e.g. for client/server coupling with another code
+  //     e.g. for client/server coupling with another code
-  //   communicator needs to shrink to be just LAMMPS
+  //     in the future LAMMPS might leverage this in other ways
-  // syntax: -mpi P1 means P1 procs for one app, P-P1 procs for second app
+  //   universe communicator needs to shrink to be just LAMMPS
-  //   LAMMPS could be either app, based on proc IDs
+  // syntax: -mpi color
+  //   color = integer for this app, different than other app(s)
   // do the following:
   //   perform an MPI_Comm_split() to create a new LAMMPS-only subcomm
-  //   NOTE: assuming other app is doing the same thing, else will hang!
+  //   NOTE: this assumes other app(s) does same thing, else will hang!
   //   re-create universe with subcomm
-  //   store full two-app comm in cscomm
+  //   store full multi-app comm in cscomm
   //   cscomm is used by CSLIB package to exchange messages w/ other app
-  // eventually should extend to N > 2 apps launched with one mpirun command
 
   int iarg = 1;
   if (narg-iarg >= 2 && (strcmp(arg[iarg],"-mpi") == 0 ||
@@ -104,13 +104,9 @@ LAMMPS::LAMMPS(int narg, char **arg, MPI_Comm communicator)
     int me,nprocs;
     MPI_Comm_rank(communicator,&me);
     MPI_Comm_size(communicator,&nprocs);
-    int p1 = atoi(arg[iarg+1]);
+    int color = atoi(arg[iarg+1]);
-    if (p1 <= 0 || p1 >= nprocs) 
-      error->universe_all(FLERR,"Invalid command-line argument");
-    int which = 0;
-    if (me >= p1) which = 1;
     MPI_Comm subcomm;
-    MPI_Comm_split(communicator,which,me,&subcomm);
+    MPI_Comm_split(communicator,color,me,&subcomm);
     cscomm = communicator;
     communicator = subcomm;
     delete universe;
@@ -656,8 +652,8 @@ LAMMPS::~LAMMPS()
   delete [] suffix;
   delete [] suffix2;
 
-  // free the MPI comm created by -mpi command-line arg
+  // free the MPI comm created by -mpi command-line arg processed in constructor
-  // it was passed to universe as if origianl universe world
+  // it was passed to universe as if original universe world
   // may have been split later by partitions, universe will free the splits
   // free a copy of uorig here, so check in universe destructor will still work