Actual source code: mpimesg.c

  1: /*$Id: mpimesg.c,v 1.14 2001/08/07 03:02:06 balay Exp $*/

 3:  #include petsc.h


  6: /*@C
  7:   PetscGatherNumberOfMessages -  Computes the number of messages a node expects to receive

  9:   Collective on MPI_Comm

 11:   Input Parameters:
 12: + comm     - Communicator
 13: . iflags   - an array of integers of length sizeof(comm). A '1' in ilengths[i] represent a 
 14:              message from current node to ith node. Optionally PETSC_NULL
 15: - ilengths - Non zero ilengths[i] represent a message to i of length ilengths[i].
 16:              Optionally PETSC_NULL.

 18:   Output Parameters:
 19: . nrecvs    - number of messages received

 21:   Level: developer

 23:   Concepts: mpi utility

 25:   Notes:
 26:   With this info, the correct message lengths can be determined using
 27:   PetscGatherMessageLengths()

 29:   Either iflags or ilengths should be provided.  If iflags is not
 30:   provided (PETSC_NULL) it can be computed from ilengths. If iflags is
 31:   provided, ilengths is not required.

 33: .seealso: PetscGatherMessageLengths()
 34: @*/
 35: int PetscGatherNumberOfMessages(MPI_Comm comm,int *iflags,int *ilengths,int *nrecvs)
 36: {
 37:   int *recv_buf,size,rank,i,ierr,*iflags_local;


 41:   MPI_Comm_size(comm,&size);
 42:   MPI_Comm_rank(comm,&rank);


 45:   /* If iflags not provided, compute iflags from ilengths */
 46:   if (!iflags) {
 47:     if (!ilengths) SETERRQ(PETSC_ERR_ARG_WRONGSTATE,"Either iflags or ilengths should be provided");
 48:     PetscMalloc(size*sizeof(int),&iflags_local);
 49:     for (i=0; i<size; i++) {
 50:       if (ilengths[i])  iflags_local[i] = 1;
 51:       else iflags_local[i] = 0;
 52:     }
 53:   } else {
 54:     iflags_local = iflags;
 55:   }

 57:   PetscMalloc(size*sizeof(int),&recv_buf);

 59:   /* Now post an allreduce to determine the numer of messages the current node will receive */
 60:   ierr    = MPI_Allreduce(iflags_local,recv_buf,size,MPI_INT,MPI_SUM,comm);
 61:   *nrecvs = recv_buf[rank];

 63:   if (!iflags) {
 64:     PetscFree(iflags_local);
 65:   }
 66:   PetscFree(recv_buf);
 67: 
 68:   return(0);
 69: }


 72: /*@C
 73:   PetscGatherMessageLengths - Computes info about messages that a MPI-node will receive, 
 74:   including (from-id,length) pairs for each message.

 76:   Collective on MPI_Comm

 78:   Input Parameters:
 79: + comm      - Communicator
 80: . nsends    - number of messages that are to be sent.
 81: . nrecvs    - number of messages being received
 82: - ilengths  - an array of integers of length sizeof(comm)
 83:               a non zero ilengths[i] represent a message to i of length ilengths[i] 


 86:   Output Parameters:
 87: + onodes    - list of node-ids from which messages are expected
 88: - olengths  - corresponding message lengths

 90:   Level: developer

 92:   Concepts: mpi utility

 94:   Notes:
 95:   With this info, the correct MPI_Irecv() can be posted with the correct
 96:   from-id, with a buffer with the right amount of memory required.

 98:   The calling function deallocates the memory in onodes and olengths

100:   To determine nrecevs, one can use PetscGatherNumberOfMessages()

102: .seealso: PetscGatherNumberOfMessages()
103: @*/
104: int PetscGatherMessageLengths(MPI_Comm comm,int nsends,int nrecvs,int *ilengths,int **onodes,int **olengths)
105: {
106:   int         size,i,j,tag,ierr;
107:   MPI_Request *s_waits,*r_waits;
108:   MPI_Status  *w_status;


112:   MPI_Comm_size(comm,&size);
113:   PetscCommGetNewTag(comm,&tag);

115:   PetscMalloc((nrecvs+nsends+1)*sizeof(MPI_Request),&r_waits);
116:   s_waits = r_waits + nrecvs;

118:   /* Now post the Irecv to get the message length-info */
119:   PetscMalloc((nrecvs+1)*sizeof(int),olengths);
120:   for (i=0; i<nrecvs; i++) {
121:     MPI_Irecv((*olengths)+i,1,MPI_INT,MPI_ANY_SOURCE,tag,comm,r_waits+i);
122:   }

124:   /* Now post the Isends with the message lenght-info */
125:   for (i=0,j=0; i<size; ++i) {
126:     if (ilengths[i]) {
127:       MPI_Isend(ilengths+i,1,MPI_INT,i,tag,comm,s_waits+j);
128:       j++;
129:     }
130:   }
131: 
132:   /* Now post waits on sends and receivs */
133:   PetscMalloc((nrecvs+nsends+1)*sizeof(MPI_Status),&w_status);
134:   MPI_Waitall(nrecvs+nsends,r_waits,w_status);

136: 
137:   /* Now pack up the received data */
138:   PetscMalloc((nrecvs+1)*sizeof(int),onodes);
139:   for (i=0; i<nrecvs; ++i) {
140:     (*onodes)[i] = w_status[i].MPI_SOURCE;
141:   }

143:   PetscFree(r_waits);
144:   PetscFree(w_status);
145: 
146:   return(0);
147: }

149: /*

151:   Allocate a bufffer sufficient to hold messages of size specified in olengths.
152:   And post Irecvs on these buffers using node info from onodes
153:   
154:  */
155: int PetscPostIrecvInt(MPI_Comm comm,int tag,int nrecvs,int *onodes,int *olengths,int ***rbuf,MPI_Request **r_waits)
156: {
157:   int         len=0,**rbuf_t,i,ierr;
158:   MPI_Request *r_waits_t;


162:   /* compute memory required for recv buffers */
163:   for (i=0; i<nrecvs; i++) len += olengths[i];  /* each message length */
164:   len *= sizeof(int);
165:   len += (nrecvs+1)*sizeof(int*); /* Array of pointers for each message */

167:   /* allocate memory for recv buffers */
168:   ierr    = PetscMalloc(len,&rbuf_t);
169:   rbuf_t[0] = (int*)(rbuf_t + nrecvs);
170:   for (i=1; i<nrecvs; ++i) rbuf_t[i] = rbuf_t[i-1] + olengths[i-1];

172:   /* Post the receives */
173:   PetscMalloc((nrecvs+1)*sizeof(MPI_Request),&r_waits_t);
174:   for (i=0; i<nrecvs; ++i) {
175:     MPI_Irecv(rbuf_t[i],olengths[i],MPI_INT,onodes[i],tag,comm,r_waits_t+i);
176:   }

178:   *rbuf    = rbuf_t;
179:   *r_waits = r_waits_t;
180:   return(0);
181: }

183: int PetscPostIrecvScalar(MPI_Comm comm,int tag,int nrecvs,int *onodes,int *olengths,PetscScalar ***rbuf,MPI_Request **r_waits)
184: {
185:   int         len=0,i,ierr;
186:   PetscScalar **rbuf_t;
187:   MPI_Request *r_waits_t;


191:   /* compute memory required for recv buffers */
192:   for (i=0; i<nrecvs; i++) len += olengths[i];  /* each message length */
193:   len *= sizeof(PetscScalar);
194:   len += (nrecvs+1)*sizeof(PetscScalar*); /* Array of pointers for each message */


197:   /* allocate memory for recv buffers */
198:   ierr    = PetscMalloc(len,&rbuf_t);
199:   rbuf_t[0] = (PetscScalar*)(rbuf_t + nrecvs);
200:   for (i=1; i<nrecvs; ++i) rbuf_t[i] = rbuf_t[i-1] + olengths[i-1];

202:   /* Post the receives */
203:   PetscMalloc((nrecvs+1)*sizeof(MPI_Request),&r_waits_t);
204:   for (i=0; i<nrecvs; ++i) {
205:     MPI_Irecv(rbuf_t[i],olengths[i],MPIU_SCALAR,onodes[i],tag,comm,r_waits_t+i);
206:   }

208:   *rbuf    = rbuf_t;
209:   *r_waits = r_waits_t;
210:   return(0);
211: }