Actual source code: tagm.c

  1: #include <petsc/private/petscimpl.h>
  2: /* ---------------------------------------------------------------- */
  3: /*
  4:    A simple way to manage tags inside a communicator.

  6:    It uses the attributes to determine if a new communicator
  7:       is needed and to store the available tags.

  9: */

 11: /*@C
 12:     PetscObjectGetNewTag - Gets a unique new tag from a PETSc object. All
 13:     processors that share the object MUST call this routine EXACTLY the same
 14:     number of times.  This tag should only be used with the current objects
 15:     communicator; do NOT use it with any other MPI communicator.

 17:     Collective on PetscObject

 19:     Input Parameter:
 20: .   obj - the PETSc object; this must be cast with a (PetscObject), for example,
 21:          PetscObjectGetNewTag((PetscObject)mat,&tag);

 23:     Output Parameter:
 24: .   tag - the new tag

 26:     Level: developer

 28: .seealso: PetscCommGetNewTag()
 29: @*/
 30: PetscErrorCode  PetscObjectGetNewTag(PetscObject obj,PetscMPIInt *tag)
 31: {
 32:   PetscCommGetNewTag(obj->comm,tag);
 33:   return 0;
 34: }

 36: /*@
 37:     PetscCommGetNewTag - Gets a unique new tag from a PETSc communicator. All
 38:     processors that share the communicator MUST call this routine EXACTLY the same
 39:     number of times.  This tag should only be used with the current objects
 40:     communicator; do NOT use it with any other MPI communicator.

 42:     Collective

 44:     Input Parameter:
 45: .   comm - the MPI communicator

 47:     Output Parameter:
 48: .   tag - the new tag

 50:     Level: developer

 52: .seealso: PetscObjectGetNewTag(), PetscCommDuplicate()
 53: @*/
 54: PetscErrorCode  PetscCommGetNewTag(MPI_Comm comm,PetscMPIInt *tag)
 55: {
 56:   PetscCommCounter *counter;
 57:   PetscMPIInt      *maxval,flg;


 61:   MPI_Comm_get_attr(comm,Petsc_Counter_keyval,&counter,&flg);

 64:   if (counter->tag < 1) {

 66:     PetscInfo(NULL,"Out of tags for object, starting to recycle. Comm reference count %" PetscInt_FMT "\n",counter->refcount);
 67:     MPI_Comm_get_attr(MPI_COMM_WORLD,MPI_TAG_UB,&maxval,&flg);
 69:     counter->tag = *maxval - 128; /* hope that any still active tags were issued right at the beginning of the run */
 70:   }

 72:   *tag = counter->tag--;
 73:   if (PetscDefined(USE_DEBUG)) {
 74:     /*
 75:      Hanging here means that some processes have called PetscCommGetNewTag() and others have not.
 76:      */
 77:     MPI_Barrier(comm);
 78:   }
 79:   return 0;
 80: }

 82: /*@C
 83:   PetscCommGetComm - get an MPI communicator from a PETSc communicator that can be passed off to another package

 85:   Collective

 87:   Input Parameter:
 88: . comm_in - Input communicator

 90:   Output Parameters:
 91: . comm_out - Output communicator

 93:   Notes:
 94:     Use PetscCommRestoreComm() to return the communicator when the external package no longer needs it

 96:     Certain MPI implementations have MPI_Comm_free() that do not work, thus one can run out of available MPI communicators causing
 97:     mysterious crashes in the code after running a long time. This routine allows reusing previously obtained MPI communicators that
 98:     are no longer needed.

100: Level: developer

102: .seealso: PetscObjectGetNewTag(), PetscCommGetNewTag(), PetscCommDestroy(), PetscCommRestoreComm()
103: @*/
104: PetscErrorCode  PetscCommGetComm(MPI_Comm comm_in,MPI_Comm *comm_out)
105: {
106:   PetscCommCounter *counter;
107:   PetscMPIInt      flg;

109:   PetscSpinlockLock(&PetscCommSpinLock);
110:   MPI_Comm_get_attr(comm_in,Petsc_Counter_keyval,&counter,&flg);

113:   if (counter->comms) {
114:     struct PetscCommStash *pcomms = counter->comms;

116:     *comm_out = pcomms->comm;
117:     counter->comms = pcomms->next;
118:     PetscFree(pcomms);
119:     PetscInfo(NULL,"Reusing a communicator %ld %ld\n",(long)comm_in,(long)*comm_out);
120:   } else {
121:     MPI_Comm_dup(comm_in,comm_out);
122:   }
123:   PetscSpinlockUnlock(&PetscCommSpinLock);
124:   return 0;
125: }

127: /*@C
128:   PetscCommRestoreComm - restores an MPI communicator that was obtained with PetscCommGetComm()

130:   Collective

132:   Input Parameters:
133: +  comm_in - Input communicator
134: -  comm_out - returned communicator

136: Level: developer

138: .seealso: PetscObjectGetNewTag(), PetscCommGetNewTag(), PetscCommDestroy(), PetscCommRestoreComm()
139: @*/
140: PetscErrorCode PetscCommRestoreComm(MPI_Comm comm_in,MPI_Comm *comm_out)
141: {
142:   PetscCommCounter      *counter;
143:   PetscMPIInt           flg;
144:   struct PetscCommStash *pcomms,*ncomm;

146:   PetscSpinlockLock(&PetscCommSpinLock);
147:   MPI_Comm_get_attr(comm_in,Petsc_Counter_keyval,&counter,&flg);

150:   PetscMalloc(sizeof(struct PetscCommStash),&ncomm);
151:   ncomm->comm = *comm_out;
152:   ncomm->next = NULL;
153:   pcomms = counter->comms;
154:   while (pcomms && pcomms->next) pcomms = pcomms->next;
155:   if (pcomms) {
156:     pcomms->next   = ncomm;
157:   } else {
158:     counter->comms = ncomm;
159:   }
160:   *comm_out = 0;
161:   PetscSpinlockUnlock(&PetscCommSpinLock);
162:   return 0;
163: }

165: /*@C
166:   PetscCommDuplicate - Duplicates the communicator only if it is not already a PETSc communicator.

168:   Collective

170:   Input Parameter:
171:   . comm_in - Input communicator

173:   Output Parameters:
174:   + comm_out - Output communicator.  May be comm_in.
175:   - first_tag - Tag available that has not already been used with this communicator (you may
176:   pass in NULL if you do not need a tag)

178:   PETSc communicators are just regular MPI communicators that keep track of which
179:   tags have been used to prevent tag conflict. If you pass a non-PETSc communicator into
180:   a PETSc creation routine it will attach a private communicator for use in the objects communications.
181:   The internal MPI_Comm is used to perform all the MPI calls for PETSc, the outer MPI_Comm is a user
182:   level MPI_Comm that may be performing communication for the user or other library and so IS NOT used by PETSc.

184: Level: developer

186: .seealso: PetscObjectGetNewTag(), PetscCommGetNewTag(), PetscCommDestroy()
187: @*/
188: PetscErrorCode  PetscCommDuplicate(MPI_Comm comm_in,MPI_Comm *comm_out,PetscMPIInt *first_tag)
189: {
190:   PetscCommCounter *counter;
191:   PetscMPIInt      *maxval,flg;

193:   PetscSpinlockLock(&PetscCommSpinLock);
194:   MPI_Comm_get_attr(comm_in,Petsc_Counter_keyval,&counter,&flg);

196:   if (!flg) {  /* this is NOT a PETSc comm */
197:     union {MPI_Comm comm; void *ptr;} ucomm;
198:     /* check if this communicator has a PETSc communicator imbedded in it */
199:     MPI_Comm_get_attr(comm_in,Petsc_InnerComm_keyval,&ucomm,&flg);
200:     if (!flg) {
201:       /* This communicator is not yet known to this system, so we duplicate it and make an internal communicator */
202:       MPI_Comm_dup(comm_in,comm_out);
203:       MPI_Comm_get_attr(MPI_COMM_WORLD,MPI_TAG_UB,&maxval,&flg);
205:       PetscNew(&counter); /* all fields of counter are zero'ed */
206:       counter->tag = *maxval;
207:       MPI_Comm_set_attr(*comm_out,Petsc_Counter_keyval,counter);
208:       PetscInfo(NULL,"Duplicating a communicator %ld %ld max tags = %d\n",(long)comm_in,(long)*comm_out,*maxval);

210:       /* save PETSc communicator inside user communicator, so we can get it next time */
211:       ucomm.comm = *comm_out;   /* ONLY the comm part of the union is significant. */
212:       MPI_Comm_set_attr(comm_in,Petsc_InnerComm_keyval,ucomm.ptr);
213:       ucomm.comm = comm_in;
214:       MPI_Comm_set_attr(*comm_out,Petsc_OuterComm_keyval,ucomm.ptr);
215:     } else {
216:       *comm_out = ucomm.comm;
217:       /* pull out the inner MPI_Comm and hand it back to the caller */
218:       MPI_Comm_get_attr(*comm_out,Petsc_Counter_keyval,&counter,&flg);
220:       PetscInfo(NULL,"Using internal PETSc communicator %ld %ld\n",(long)comm_in,(long)*comm_out);
221:     }
222:   } else *comm_out = comm_in;

224:   if (PetscDefined(USE_DEBUG)) {
225:     /*
226:      Hanging here means that some processes have called PetscCommDuplicate() and others have not.
227:      This likley means that a subset of processes in a MPI_Comm have attempted to create a PetscObject!
228:      ALL processes that share a communicator MUST shared objects created from that communicator.
229:      */
230:     MPI_Barrier(comm_in);
231:   }

233:   if (counter->tag < 1) {
234:     PetscInfo(NULL,"Out of tags for object, starting to recycle. Comm reference count %" PetscInt_FMT "\n",counter->refcount);
235:     MPI_Comm_get_attr(MPI_COMM_WORLD,MPI_TAG_UB,&maxval,&flg);
237:     counter->tag = *maxval - 128; /* hope that any still active tags were issued right at the beginning of the run */
238:   }

240:   if (first_tag) *first_tag = counter->tag--;

242:   counter->refcount++; /* number of references to this comm */
243:   PetscSpinlockUnlock(&PetscCommSpinLock);
244:   return 0;
245: }

247: /*@C
248:    PetscCommDestroy - Frees communicator.  Use in conjunction with PetscCommDuplicate().

250:    Collective

252:    Input Parameter:
253: .  comm - the communicator to free

255:    Level: developer

257: .seealso:   PetscCommDuplicate()
258: @*/
259: PetscErrorCode  PetscCommDestroy(MPI_Comm *comm)
260: {
261:   PetscCommCounter *counter;
262:   PetscMPIInt      flg;
263:   MPI_Comm         icomm = *comm,ocomm;
264:   union {MPI_Comm comm; void *ptr;} ucomm;

266:   if (*comm == MPI_COMM_NULL) return 0;
267:   PetscSpinlockLock(&PetscCommSpinLock);
268:   MPI_Comm_get_attr(icomm,Petsc_Counter_keyval,&counter,&flg);
269:   if (!flg) { /* not a PETSc comm, check if it has an inner comm */
270:     MPI_Comm_get_attr(icomm,Petsc_InnerComm_keyval,&ucomm,&flg);
272:     icomm = ucomm.comm;
273:     MPI_Comm_get_attr(icomm,Petsc_Counter_keyval,&counter,&flg);
275:   }

277:   counter->refcount--;

279:   if (!counter->refcount) {
280:     /* if MPI_Comm has outer comm then remove reference to inner MPI_Comm from outer MPI_Comm */
281:     MPI_Comm_get_attr(icomm,Petsc_OuterComm_keyval,&ucomm,&flg);
282:     if (flg) {
283:       ocomm = ucomm.comm;
284:       MPI_Comm_get_attr(ocomm,Petsc_InnerComm_keyval,&ucomm,&flg);
285:       if (flg) {
286:         MPI_Comm_delete_attr(ocomm,Petsc_InnerComm_keyval);
287:       } else SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_CORRUPT,"Outer MPI_Comm %ld does not have expected reference to inner comm %ld, problem with corrupted memory",(long int)ocomm,(long int)icomm);
288:     }

290:     PetscInfo(NULL,"Deleting PETSc MPI_Comm %ld\n",(long)icomm);
291:     MPI_Comm_free(&icomm);
292:   }
293:   *comm = MPI_COMM_NULL;
294:   PetscSpinlockUnlock(&PetscCommSpinLock);
295:   return 0;
296: }

298: /*@C
299:     PetscObjectsListGetGlobalNumbering - computes a global numbering
300:     of PetscObjects living on subcommunicators of a given communicator.

302:     Collective.

304:     Input Parameters:
305: +   comm    - MPI_Comm
306: .   len     - local length of objlist
307: -   objlist - a list of PETSc objects living on subcomms of comm and containing this comm rank
308:               (subcomm ordering is assumed to be deadlock-free)

310:     Output Parameters:
311: +   count      - global number of distinct subcommunicators on objlist (may be > len)
312: -   numbering  - global numbers of objlist entries (allocated by user)

314:     Level: developer

316: @*/
317: PetscErrorCode  PetscObjectsListGetGlobalNumbering(MPI_Comm comm, PetscInt len, PetscObject *objlist, PetscInt *count, PetscInt *numbering)
318: {
319:   PetscInt       i, roots, offset;
320:   PetscMPIInt    size, rank;

323:   if (!count && !numbering) return 0;

325:   MPI_Comm_size(comm, &size);
326:   MPI_Comm_rank(comm, &rank);
327:   roots = 0;
328:   for (i = 0; i < len; ++i) {
329:     PetscMPIInt srank;
330:     MPI_Comm_rank(objlist[i]->comm, &srank);
331:     /* Am I the root of the i-th subcomm? */
332:     if (!srank) ++roots;
333:   }
334:   if (count) {
335:     /* Obtain the sum of all roots -- the global number of distinct subcomms. */
336:     MPIU_Allreduce(&roots,count,1,MPIU_INT,MPI_SUM,comm);
337:   }
338:   if (numbering) {
339:     /* Introduce a global numbering for subcomms, initially known only by subcomm roots. */
340:     /*
341:       At each subcomm root number all of the subcomms it owns locally
342:       and make it global by calculating the shift among all of the roots.
343:       The roots are ordered using the comm ordering.
344:     */
345:     MPI_Scan(&roots,&offset,1,MPIU_INT,MPI_SUM,comm);
346:     offset -= roots;
347:     /* Now we are ready to broadcast global subcomm numbers within each subcomm.*/
348:     /*
349:       This is where the assumption of a deadlock-free ordering of the subcomms is assumed:
350:       broadcast is collective on the subcomm.
351:     */
352:     roots = 0;
353:     for (i = 0; i < len; ++i) {
354:       PetscMPIInt srank;
355:       numbering[i] = offset + roots; /* only meaningful if !srank. */

357:       MPI_Comm_rank(objlist[i]->comm, &srank);
358:       MPI_Bcast(numbering+i,1,MPIU_INT,0,objlist[i]->comm);
359:       if (!srank) ++roots;
360:     }
361:   }
362:   return 0;
363: }