1: #include <petsc/private/viewerimpl.h>
  2: #include <petscdraw.h>

  4: PetscClassId PETSC_VIEWER_CLASSID;

  6: static PetscBool PetscViewerPackageInitialized = PETSC_FALSE;

  8: /*@C
  9:   PetscViewerFinalizePackage - This function destroys any global objects created in PETSc viewers. It is
 10:   called from `PetscFinalize()`.

 12:   Level: developer

 14: .seealso: [](sec_viewers), `PetscViewer`, `PetscFinalize()`, `PetscViewerInitializePackage()`
 15: @*/
 16: PetscErrorCode PetscViewerFinalizePackage(void)
 17: {
 18:   PetscFunctionBegin;
 19:   if (Petsc_Viewer_keyval != MPI_KEYVAL_INVALID) PetscCallMPI(MPI_Comm_free_keyval(&Petsc_Viewer_keyval));
 20:   if (Petsc_Viewer_Stdout_keyval != MPI_KEYVAL_INVALID) PetscCallMPI(MPI_Comm_free_keyval(&Petsc_Viewer_Stdout_keyval));
 21:   if (Petsc_Viewer_Stderr_keyval != MPI_KEYVAL_INVALID) PetscCallMPI(MPI_Comm_free_keyval(&Petsc_Viewer_Stderr_keyval));
 22:   if (Petsc_Viewer_Binary_keyval != MPI_KEYVAL_INVALID) PetscCallMPI(MPI_Comm_free_keyval(&Petsc_Viewer_Binary_keyval));
 23:   if (Petsc_Viewer_Draw_keyval != MPI_KEYVAL_INVALID) PetscCallMPI(MPI_Comm_free_keyval(&Petsc_Viewer_Draw_keyval));
 24: #if defined(PETSC_HAVE_HDF5)
 25:   if (Petsc_Viewer_HDF5_keyval != MPI_KEYVAL_INVALID) PetscCallMPI(MPI_Comm_free_keyval(&Petsc_Viewer_HDF5_keyval));
 26: #endif
 27: #if defined(PETSC_USE_SOCKETVIEWER)
 28:   if (Petsc_Viewer_Socket_keyval != MPI_KEYVAL_INVALID) PetscCallMPI(MPI_Comm_free_keyval(&Petsc_Viewer_Socket_keyval));
 29: #endif
 30:   PetscCall(PetscFunctionListDestroy(&PetscViewerList));
 31:   PetscViewerPackageInitialized = PETSC_FALSE;
 32:   PetscViewerRegisterAllCalled  = PETSC_FALSE;
 33:   PetscFunctionReturn(PETSC_SUCCESS);
 34: }

 36: /*@C
 37:   PetscViewerInitializePackage - This function initializes everything in the `PetscViewer` package.

 39:   Level: developer

 41: .seealso: [](sec_viewers), `PetscViewer`, `PetscInitialize()`, `PetscViewerFinalizePackage()`
 42: @*/
 43: PetscErrorCode PetscViewerInitializePackage(void)
 44: {
 45:   char      logList[256];
 46:   PetscBool opt, pkg;

 48:   PetscFunctionBegin;
 49:   if (PetscViewerPackageInitialized) PetscFunctionReturn(PETSC_SUCCESS);
 50:   PetscViewerPackageInitialized = PETSC_TRUE;
 51:   /* Register Classes */
 52:   PetscCall(PetscClassIdRegister("Viewer", &PETSC_VIEWER_CLASSID));
 53:   /* Register Constructors */
 54:   PetscCall(PetscViewerRegisterAll());
 55:   /* Process Info */
 56:   {
 57:     PetscClassId classids[1];

 59:     classids[0] = PETSC_VIEWER_CLASSID;
 60:     PetscCall(PetscInfoProcessClass("viewer", 1, classids));
 61:   }
 62:   /* Process summary exclusions */
 63:   PetscCall(PetscOptionsGetString(NULL, NULL, "-log_exclude", logList, sizeof(logList), &opt));
 64:   if (opt) {
 65:     PetscCall(PetscStrInList("viewer", logList, ',', &pkg));
 66:     if (pkg) PetscCall(PetscLogEventExcludeClass(PETSC_VIEWER_CLASSID));
 67:   }
 68: #if defined(PETSC_HAVE_MATHEMATICA)
 69:   PetscCall(PetscViewerMathematicaInitializePackage());
 70: #endif
 71:   /* Register package finalizer */
 72:   PetscCall(PetscRegisterFinalize(PetscViewerFinalizePackage));
 73:   PetscFunctionReturn(PETSC_SUCCESS);
 74: }

 76: /*@
 77:   PetscViewerDestroy - Destroys a `PetscViewer`.

 79:   Collective

 81:   Input Parameter:
 82: . viewer - the `PetscViewer` to be destroyed.

 84:   Level: beginner

 86: .seealso: [](sec_viewers), `PetscViewer`, `PetscViewerCreate()`, `PetscViewerSocketOpen()`, `PetscViewerASCIIOpen()`, `PetscViewerDrawOpen()`
 87: @*/
 88: PetscErrorCode PetscViewerDestroy(PetscViewer *viewer)
 89: {
 90:   PetscFunctionBegin;
 91:   if (!*viewer) PetscFunctionReturn(PETSC_SUCCESS);

 94:   PetscCall(PetscViewerFlush(*viewer));
 95:   if (--((PetscObject)(*viewer))->refct > 0) {
 96:     *viewer = NULL;
 97:     PetscFunctionReturn(PETSC_SUCCESS);
 98:   }

100:   PetscCall(PetscObjectSAWsViewOff((PetscObject)*viewer));
101:   if ((*viewer)->ops->destroy) PetscCall((*(*viewer)->ops->destroy)(*viewer));
102:   PetscCall(PetscHeaderDestroy(viewer));
103:   PetscFunctionReturn(PETSC_SUCCESS);
104: }

106: /*@C
107:   PetscViewerAndFormatCreate - Creates a `PetscViewerAndFormat` struct.

109:   Collective

111:   Input Parameters:
112: + viewer - the viewer
113: - format - the format

115:   Output Parameter:
116: . vf - viewer and format object

118:   Level: developer

120:   Notes:
121:   This increases the reference count of the viewer.

123:   Use `PetscViewerAndFormatDestroy()` to free the struct

125:   This is used as the context variable for many of the `TS`, `SNES`, and `KSP` monitor functions

127:   This construct exists because it allows one to keep track of the use of a `PetscViewerFormat` without requiring the
128:   format in the viewer to be permanently changed.

130: .seealso: [](sec_viewers), `PetscViewer`, `PetscViewerAndFormat`, `PetscViewerFormat`, `PetscViewerSocketOpen()`, `PetscViewerASCIIOpen()`, `PetscViewerCreate()`,
131:           `PetscViewerDrawOpen()`, `PetscViewerAndFormatDestroy()`
132: @*/
133: PetscErrorCode PetscViewerAndFormatCreate(PetscViewer viewer, PetscViewerFormat format, PetscViewerAndFormat **vf)
134: {
135:   PetscFunctionBegin;
136:   PetscCall(PetscObjectReference((PetscObject)viewer));
137:   PetscCall(PetscNew(vf));
138:   (*vf)->viewer = viewer;
139:   (*vf)->format = format;
140:   (*vf)->lg     = NULL;
141:   (*vf)->data   = NULL;
142:   PetscFunctionReturn(PETSC_SUCCESS);
143: }

145: /*@C
146:   PetscViewerAndFormatDestroy - Destroys a `PetscViewerAndFormat` struct created with `PetscViewerAndFormatCreate()`

148:   Collective

150:   Input Parameter:
151: . vf - the `PetscViewerAndFormat` to be destroyed.

153:   Level: developer

155: .seealso: [](sec_viewers), `PetscViewer`, `PetscViewerAndFormat`, `PetscViewerFormat`, `PetscViewerAndFormatCreate()`, `PetscViewerSocketOpen()`,
156:           `PetscViewerASCIIOpen()`, `PetscViewerCreate()`, `PetscViewerDrawOpen()`
157: @*/
158: PetscErrorCode PetscViewerAndFormatDestroy(PetscViewerAndFormat **vf)
159: {
160:   PetscFunctionBegin;
161:   PetscCall(PetscViewerDestroy(&(*vf)->viewer));
162:   PetscCall(PetscDrawLGDestroy(&(*vf)->lg));
163:   PetscCall(PetscFree(*vf));
164:   PetscFunctionReturn(PETSC_SUCCESS);
165: }

167: /*@C
168:   PetscViewerGetType - Returns the type of a `PetscViewer`.

170:   Not Collective

172:   Input Parameter:
173: . viewer - the `PetscViewer`

175:   Output Parameter:
176: . type - `PetscViewerType`

178:   Level: intermediate

180:   Note:
181:   `PetscViewerType` is actually a string

183: .seealso: [](sec_viewers), `PetscViewerType`, `PetscViewer`, `PetscViewerCreate()`, `PetscViewerSetType()`
184: @*/
185: PetscErrorCode PetscViewerGetType(PetscViewer viewer, PetscViewerType *type)
186: {
187:   PetscFunctionBegin;
189:   PetscAssertPointer(type, 2);
190:   *type = ((PetscObject)viewer)->type_name;
191:   PetscFunctionReturn(PETSC_SUCCESS);
192: }

194: /*@C
195:   PetscViewerSetOptionsPrefix - Sets the prefix used for searching for
196:   `PetscViewer` options in the database during `PetscViewerSetFromOptions()`.

198:   Logically Collective

200:   Input Parameters:
201: + viewer - the `PetscViewer` context
202: - prefix - the prefix to prepend to all option names

204:   Note:
205:   A hyphen (-) must NOT be given at the beginning of the prefix name.
206:   The first character of all runtime options is AUTOMATICALLY the hyphen.

208:   Level: advanced

210: .seealso: [](sec_viewers), `PetscViewer`, `PetscViewerSetFromOptions()`, `PetscViewerAppendOptionsPrefix()`
211: @*/
212: PetscErrorCode PetscViewerSetOptionsPrefix(PetscViewer viewer, const char prefix[])
213: {
214:   PetscFunctionBegin;
216:   PetscCall(PetscObjectSetOptionsPrefix((PetscObject)viewer, prefix));
217:   PetscFunctionReturn(PETSC_SUCCESS);
218: }

220: /*@C
221:   PetscViewerAppendOptionsPrefix - Appends to the prefix used for searching for
222:   `PetscViewer` options in the database during `PetscViewerSetFromOptions()`.

224:   Logically Collective

226:   Input Parameters:
227: + viewer - the `PetscViewer` context
228: - prefix - the prefix to prepend to all option names

230:   Level: advanced

232:   Note:
233:   A hyphen (-) must NOT be given at the beginning of the prefix name.
234:   The first character of all runtime options is AUTOMATICALLY the hyphen.

236: .seealso: [](sec_viewers), `PetscViewer`, `PetscViewerGetOptionsPrefix()`, `PetscViewerSetOptionsPrefix()`
237: @*/
238: PetscErrorCode PetscViewerAppendOptionsPrefix(PetscViewer viewer, const char prefix[])
239: {
240:   PetscFunctionBegin;
242:   PetscCall(PetscObjectAppendOptionsPrefix((PetscObject)viewer, prefix));
243:   PetscFunctionReturn(PETSC_SUCCESS);
244: }

246: /*@C
247:   PetscViewerGetOptionsPrefix - Gets the prefix used for searching for
248:   `PetscViewer` options in the database during `PetscViewerSetFromOptions()`.

250:   Not Collective

252:   Input Parameter:
253: . viewer - the `PetscViewer` context

255:   Output Parameter:
256: . prefix - pointer to the prefix string used

258:   Level: advanced

260:   Fortran Notes:
261:   The user should pass in a string 'prefix' of sufficient length to hold the prefix.

263: .seealso: [](sec_viewers), `PetscViewer`, `PetscViewerAppendOptionsPrefix()`, `PetscViewerSetOptionsPrefix()`
264: @*/
265: PetscErrorCode PetscViewerGetOptionsPrefix(PetscViewer viewer, const char *prefix[])
266: {
267:   PetscFunctionBegin;
269:   PetscCall(PetscObjectGetOptionsPrefix((PetscObject)viewer, prefix));
270:   PetscFunctionReturn(PETSC_SUCCESS);
271: }

273: /*@
274:   PetscViewerSetUp - Sets up the internal viewer data structures for the later use.

276:   Collective

278:   Input Parameter:
279: . viewer - the `PetscViewer` context

281:   Level: advanced

283:   Note:
284:   For basic use of the `PetscViewer` classes the user need not explicitly call
285:   `PetscViewerSetUp()`, since these actions will happen automatically.

287: .seealso: [](sec_viewers), `PetscViewer`, `PetscViewerCreate()`, `PetscViewerDestroy()`
288: @*/
289: PetscErrorCode PetscViewerSetUp(PetscViewer viewer)
290: {
291:   PetscFunctionBegin;
293:   if (viewer->setupcalled) PetscFunctionReturn(PETSC_SUCCESS);
294:   PetscTryTypeMethod(viewer, setup);
295:   viewer->setupcalled = PETSC_TRUE;
296:   PetscFunctionReturn(PETSC_SUCCESS);
297: }

299: /*@C
300:   PetscViewerViewFromOptions - View from the viewer based on options in the options database

302:   Collective

304:   Input Parameters:
305: + A    - the `PetscViewer` context
306: . obj  - Optional object that provides the prefix for the option names
307: - name - command line option

309:   Level: intermediate

311:   Note:
312:   See `PetscObjectViewFromOptions()` for details on the viewers and formats support via this interface

314: .seealso: [](sec_viewers), `PetscViewer`, `PetscViewerView`, `PetscObjectViewFromOptions()`, `PetscViewerCreate()`
315: @*/
316: PetscErrorCode PetscViewerViewFromOptions(PetscViewer A, PetscObject obj, const char name[])
317: {
318:   PetscFunctionBegin;
320:   PetscCall(PetscObjectViewFromOptions((PetscObject)A, obj, name));
321:   PetscFunctionReturn(PETSC_SUCCESS);
322: }

324: /*@C
325:   PetscViewerView - Visualizes a viewer object.

327:   Collective

329:   Input Parameters:
330: + v      - the viewer to be viewed
331: - viewer - visualization context

333:   Level: beginner

335: .seealso: [](sec_viewers), `PetscViewer`, `PetscViewerPushFormat()`, `PetscViewerASCIIOpen()`, `PetscViewerDrawOpen()`,
336:           `PetscViewerSocketOpen()`, `PetscViewerBinaryOpen()`, `PetscViewerLoad()`
337: @*/
338: PetscErrorCode PetscViewerView(PetscViewer v, PetscViewer viewer)
339: {
340:   PetscBool         iascii;
341:   PetscViewerFormat format;
342: #if defined(PETSC_HAVE_SAWS)
343:   PetscBool issaws;
344: #endif

346:   PetscFunctionBegin;
349:   if (!viewer) PetscCall(PetscViewerASCIIGetStdout(PetscObjectComm((PetscObject)v), &viewer));
351:   PetscCheckSameComm(v, 1, viewer, 2);

353:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERASCII, &iascii));
354: #if defined(PETSC_HAVE_SAWS)
355:   PetscCall(PetscObjectTypeCompare((PetscObject)viewer, PETSCVIEWERSAWS, &issaws));
356: #endif
357:   if (iascii) {
358:     PetscCall(PetscViewerGetFormat(viewer, &format));
359:     PetscCall(PetscObjectPrintClassNamePrefixType((PetscObject)v, viewer));
360:     if (format == PETSC_VIEWER_DEFAULT || format == PETSC_VIEWER_ASCII_INFO || format == PETSC_VIEWER_ASCII_INFO_DETAIL) {
361:       if (v->format) PetscCall(PetscViewerASCIIPrintf(viewer, "  Viewer format = %s\n", PetscViewerFormats[v->format]));
362:       PetscCall(PetscViewerASCIIPushTab(viewer));
363:       PetscTryTypeMethod(v, view, viewer);
364:       PetscCall(PetscViewerASCIIPopTab(viewer));
365:     }
366: #if defined(PETSC_HAVE_SAWS)
367:   } else if (issaws) {
368:     if (!((PetscObject)v)->amsmem) {
369:       PetscCall(PetscObjectViewSAWs((PetscObject)v, viewer));
370:       PetscTryTypeMethod(v, view, viewer);
371:     }
372: #endif
373:   }
374:   PetscFunctionReturn(PETSC_SUCCESS);
375: }

377: /*@C
378:   PetscViewerRead - Reads data from a `PetscViewer`

380:   Collective

382:   Input Parameters:
383: + viewer - The viewer
384: . data   - Location to write the data, treated as an array of the type defined by `datatype`
385: . num    - Number of items of data to read
386: - dtype  - Type of data to read

388:   Output Parameter:
389: . count - number of items of data actually read, or `NULL`

391:   Level: beginner

393:   Notes:
394:   If datatype is `PETSC_STRING` and `num` is negative, reads until a newline character is found,
395:   until a maximum of (-num - 1) chars.

397:   Only certain viewers, such as `PETSCVIEWERBINARY` can be read from, see `PetscViewerReadable()`

399: .seealso: [](sec_viewers), `PetscViewer`, `PetscViewerASCIIOpen()`, `PetscViewerPushFormat()`, `PetscViewerDestroy()`,
400:           `PetscViewerReadable()`, `PetscViewerBinaryGetDescriptor()`,
401:           `PetscViewerBinaryGetInfoPointer()`, `PetscFileMode`
402: @*/
403: PetscErrorCode PetscViewerRead(PetscViewer viewer, void *data, PetscInt num, PetscInt *count, PetscDataType dtype)
404: {
405:   PetscFunctionBegin;
407:   if (dtype == PETSC_STRING) {
408:     PetscInt c, i = 0, cnt;
409:     char    *s = (char *)data;
410:     if (num >= 0) {
411:       for (c = 0; c < num; c++) {
412:         /* Skip leading whitespaces */
413:         do {
414:           PetscCall((*viewer->ops->read)(viewer, &(s[i]), 1, &cnt, PETSC_CHAR));
415:           if (!cnt) break;
416:         } while (s[i] == '\n' || s[i] == '\t' || s[i] == ' ' || s[i] == '\0' || s[i] == '\v' || s[i] == '\f' || s[i] == '\r');
417:         i++;
418:         /* Read strings one char at a time */
419:         do {
420:           PetscCall((*viewer->ops->read)(viewer, &(s[i++]), 1, &cnt, PETSC_CHAR));
421:           if (!cnt) break;
422:         } while (s[i - 1] != '\n' && s[i - 1] != '\t' && s[i - 1] != ' ' && s[i - 1] != '\0' && s[i - 1] != '\v' && s[i - 1] != '\f' && s[i - 1] != '\r');
423:         /* Terminate final string */
424:         if (c == num - 1) s[i - 1] = '\0';
425:       }
426:     } else {
427:       /* Read until a \n is encountered (-num is the max size allowed) */
428:       do {
429:         PetscCall((*viewer->ops->read)(viewer, &(s[i++]), 1, &cnt, PETSC_CHAR));
430:         if (i == -num || !cnt) break;
431:       } while (s[i - 1] != '\n');
432:       /* Terminate final string */
433:       s[i - 1] = '\0';
434:       c        = i;
435:     }
436:     if (count) *count = c;
437:     else PetscCheck(c >= num, PetscObjectComm((PetscObject)viewer), PETSC_ERR_FILE_READ, "Insufficient data, only read %" PetscInt_FMT " < %" PetscInt_FMT " strings", c, num);
438:   } else PetscUseTypeMethod(viewer, read, data, num, count, dtype);
439:   PetscFunctionReturn(PETSC_SUCCESS);
440: }

442: /*@
443:   PetscViewerReadable - Return a flag whether the viewer can be read from with `PetscViewerRead()`

445:   Not Collective

447:   Input Parameter:
448: . viewer - the `PetscViewer` context

450:   Output Parameter:
451: . flg - `PETSC_TRUE` if the viewer is readable, `PETSC_FALSE` otherwise

453:   Level: intermediate

455:   Note:
456:   `PETSC_TRUE` means that viewer's `PetscViewerType` supports reading, that is `PetscViewerRead()`, (this holds e.g. for `PETSCVIEWERBINARY`)
457:   and the viewer is in a mode allowing reading, i.e. `PetscViewerFileGetMode()`
458:   returns one of `FILE_MODE_READ`, `FILE_MODE_UPDATE`, `FILE_MODE_APPEND_UPDATE`.

460: .seealso: [](sec_viewers), `PetscViewerRead()`, `PetscViewer`, `PetscViewerWritable()`, `PetscViewerCheckReadable()`, `PetscViewerCreate()`, `PetscViewerFileSetMode()`, `PetscViewerFileSetType()`
461: @*/
462: PetscErrorCode PetscViewerReadable(PetscViewer viewer, PetscBool *flg)
463: {
464:   PetscFileMode mode;
465:   PetscErrorCode (*f)(PetscViewer, PetscFileMode *) = NULL;

467:   PetscFunctionBegin;
469:   PetscAssertPointer(flg, 2);
470:   PetscCall(PetscObjectQueryFunction((PetscObject)viewer, "PetscViewerFileGetMode_C", &f));
471:   *flg = PETSC_FALSE;
472:   if (!f) PetscFunctionReturn(PETSC_SUCCESS);
473:   PetscCall((*f)(viewer, &mode));
474:   switch (mode) {
475:   case FILE_MODE_READ:
476:   case FILE_MODE_UPDATE:
477:   case FILE_MODE_APPEND_UPDATE:
478:     *flg = PETSC_TRUE;
479:   default:
480:     break;
481:   }
482:   PetscFunctionReturn(PETSC_SUCCESS);
483: }

485: /*@
486:   PetscViewerWritable - Return a flag whether the viewer can be written to with `PetscViewerWrite()`

488:   Not Collective

490:   Input Parameter:
491: . viewer - the `PetscViewer` context

493:   Output Parameter:
494: . flg - `PETSC_TRUE` if the viewer is writable, `PETSC_FALSE` otherwise

496:   Level: intermediate

498:   Note:
499:   `PETSC_TRUE` means viewer is in a mode allowing writing, i.e. `PetscViewerFileGetMode()`
500:   returns one of `FILE_MODE_WRITE`, `FILE_MODE_APPEND`, `FILE_MODE_UPDATE`, `FILE_MODE_APPEND_UPDATE`.

502: .seealso: [](sec_viewers), `PetscViewer`, `PetscViewerReadable()`, `PetscViewerCheckWritable()`, `PetscViewerCreate()`, `PetscViewerFileSetMode()`, `PetscViewerFileSetType()`
503: @*/
504: PetscErrorCode PetscViewerWritable(PetscViewer viewer, PetscBool *flg)
505: {
506:   PetscFileMode mode;
507:   PetscErrorCode (*f)(PetscViewer, PetscFileMode *) = NULL;

509:   PetscFunctionBegin;
511:   PetscAssertPointer(flg, 2);
512:   PetscCall(PetscObjectQueryFunction((PetscObject)viewer, "PetscViewerFileGetMode_C", &f));
513:   *flg = PETSC_TRUE;
514:   if (!f) PetscFunctionReturn(PETSC_SUCCESS);
515:   PetscCall((*f)(viewer, &mode));
516:   if (mode == FILE_MODE_READ) *flg = PETSC_FALSE;
517:   PetscFunctionReturn(PETSC_SUCCESS);
518: }

520: /*@
521:   PetscViewerCheckReadable - Check whether the viewer can be read from, generates an error if not

523:   Collective

525:   Input Parameter:
526: . viewer - the `PetscViewer` context

528:   Level: intermediate

530: .seealso: [](sec_viewers), `PetscViewer`, `PetscViewerReadable()`, `PetscViewerCheckWritable()`, `PetscViewerCreate()`, `PetscViewerFileSetMode()`, `PetscViewerFileSetType()`
531: @*/
532: PetscErrorCode PetscViewerCheckReadable(PetscViewer viewer)
533: {
534:   PetscBool flg;

536:   PetscFunctionBegin;
538:   PetscCall(PetscViewerReadable(viewer, &flg));
539:   PetscCheck(flg, PetscObjectComm((PetscObject)viewer), PETSC_ERR_SUP, "Viewer doesn't support reading, or is not in reading mode (FILE_MODE_READ, FILE_MODE_UPDATE, FILE_MODE_APPEND_UPDATE)");
540:   PetscFunctionReturn(PETSC_SUCCESS);
541: }

543: /*@
544:   PetscViewerCheckWritable - Check whether the viewer can be written to, generates an error if not

546:   Collective

548:   Input Parameter:
549: . viewer - the `PetscViewer` context

551:   Level: intermediate

553: .seealso: [](sec_viewers), `PetscViewer`, `PetscViewerWritable()`, `PetscViewerCheckReadable()`, `PetscViewerCreate()`, `PetscViewerFileSetMode()`, `PetscViewerFileSetType()`
554: @*/
555: PetscErrorCode PetscViewerCheckWritable(PetscViewer viewer)
556: {
557:   PetscBool flg;

559:   PetscFunctionBegin;
561:   PetscCall(PetscViewerWritable(viewer, &flg));
562:   PetscCheck(flg, PetscObjectComm((PetscObject)viewer), PETSC_ERR_SUP, "Viewer doesn't support writing, or is in FILE_MODE_READ mode");
563:   PetscFunctionReturn(PETSC_SUCCESS);
564: }