2:  #include <petscsys.h>
  3:  #include <petsc/private/petscimpl.h>
  4: /*
  5:     Note that tag of 0 is ok because comm is a private communicator
  6:   generated below just for these routines.
  7: */

  9: PetscErrorCode PetscSequentialPhaseBegin_Private(MPI_Comm comm,int ng)
 10: {
 12:   PetscMPIInt    rank,size,tag = 0;
 13:   MPI_Status     status;

 16:   MPI_Comm_size(comm,&size);
 17:   if (size == 1) return(0);
 18:   MPI_Comm_rank(comm,&rank);
 19:   if (rank) {
 20:     MPI_Recv(0,0,MPI_INT,rank-1,tag,comm,&status);
 21:   }
 22:   /* Send to the next process in the group unless we are the last process */
 23:   if ((rank % ng) < ng - 1 && rank != size - 1) {
 24:     MPI_Send(0,0,MPI_INT,rank + 1,tag,comm);
 25:   }
 26:   return(0);
 27: }

 29: PetscErrorCode PetscSequentialPhaseEnd_Private(MPI_Comm comm,int ng)
 30: {
 32:   PetscMPIInt    rank,size,tag = 0;
 33:   MPI_Status     status;

 36:   MPI_Comm_rank(comm,&rank);
 37:   MPI_Comm_size(comm,&size);
 38:   if (size == 1) return(0);

 40:   /* Send to the first process in the next group */
 41:   if ((rank % ng) == ng - 1 || rank == size - 1) {
 42:     MPI_Send(0,0,MPI_INT,(rank + 1) % size,tag,comm);
 43:   }
 44:   if (!rank) {
 45:     MPI_Recv(0,0,MPI_INT,size-1,tag,comm,&status);
 46:   }
 47:   return(0);
 48: }

 50: /* ---------------------------------------------------------------------*/
 51: /*
 52:     The variable Petsc_Seq_keyval is used to indicate an MPI attribute that
 53:   is attached to a communicator that manages the sequential phase code below.
 54: */
 55: PetscMPIInt Petsc_Seq_keyval = MPI_KEYVAL_INVALID;

 57: /*@
 58:    PetscSequentialPhaseBegin - Begins a sequential section of code.

 60:    Collective on MPI_Comm

 62:    Input Parameters:
 63: +  comm - Communicator to sequentialize.
 64: -  ng   - Number in processor group.  This many processes are allowed to execute
 65:    at the same time (usually 1)

 67:    Level: intermediate

 69:    Notes:
 70:    PetscSequentialPhaseBegin() and PetscSequentialPhaseEnd() provide a
 71:    way to force a section of code to be executed by the processes in
 72:    rank order.  Typically, this is done with
 73: .vb
 74:       PetscSequentialPhaseBegin(comm, 1);
 75:       <code to be executed sequentially>
 76:       PetscSequentialPhaseEnd(comm, 1);
 77: .ve

 79:    Often, the sequential code contains output statements (e.g., printf) to
 80:    be executed.  Note that you may need to flush the I/O buffers before
 81:    calling PetscSequentialPhaseEnd().  Also, note that some systems do
 82:    not propagate I/O in any order to the controling terminal (in other words,
 83:    even if you flush the output, you may not get the data in the order
 84:    that you want).

 86: .seealso: PetscSequentialPhaseEnd()

 88:    Concepts: sequential stage

 90: @*/
 91: PetscErrorCode  PetscSequentialPhaseBegin(MPI_Comm comm,int ng)
 92: {
 94:   PetscMPIInt    size;
 95:   MPI_Comm       local_comm,*addr_local_comm;

 98:   MPI_Comm_size(comm,&size);
 99:   if (size == 1) return(0);

101:   /* Get the private communicator for the sequential operations */
102:   if (Petsc_Seq_keyval == MPI_KEYVAL_INVALID) {
103:     MPI_Keyval_create(MPI_NULL_COPY_FN,MPI_NULL_DELETE_FN,&Petsc_Seq_keyval,0);
104:   }

106:   MPI_Comm_dup(comm,&local_comm);
107:   PetscMalloc1(1,&addr_local_comm);

109:   *addr_local_comm = local_comm;

111:   MPI_Attr_put(comm,Petsc_Seq_keyval,(void*)addr_local_comm);
112:   PetscSequentialPhaseBegin_Private(local_comm,ng);
113:   return(0);
114: }

116: /*@
117:    PetscSequentialPhaseEnd - Ends a sequential section of code.

119:    Collective on MPI_Comm

121:    Input Parameters:
122: +  comm - Communicator to sequentialize.
123: -  ng   - Number in processor group.  This many processes are allowed to execute
124:    at the same time (usually 1)

126:    Level: intermediate

128:    Notes:
129:    See PetscSequentialPhaseBegin() for more details.

131: .seealso: PetscSequentialPhaseBegin()

133:    Concepts: sequential stage

135: @*/
136: PetscErrorCode  PetscSequentialPhaseEnd(MPI_Comm comm,int ng)
137: {
139:   PetscMPIInt    size,flag;
140:   MPI_Comm       local_comm,*addr_local_comm;

143:   MPI_Comm_size(comm,&size);
144:   if (size == 1) return(0);

146:   MPI_Attr_get(comm,Petsc_Seq_keyval,(void**)&addr_local_comm,&flag);
147:   if (!flag) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_INCOMP,"Wrong MPI communicator; must pass in one used with PetscSequentialPhaseBegin()");
148:   local_comm = *addr_local_comm;

150:   PetscSequentialPhaseEnd_Private(local_comm,ng);

152:   PetscFree(addr_local_comm);
153:   MPI_Comm_free(&local_comm);
154:   MPI_Attr_delete(comm,Petsc_Seq_keyval);
155:   return(0);
156: }