summaryrefslogtreecommitdiffstats
path: root/src/H5Cmpio.c
blob: 810398963058653bc600c709ffc484fe6b647627 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright by The HDF Group.                                               *
 * Copyright by the Board of Trustees of the University of Illinois.         *
 * All rights reserved.                                                      *
 *                                                                           *
 * This file is part of HDF5.  The full HDF5 copyright notice, including     *
 * terms governing use, modification, and redistribution, is contained in    *
 * the COPYING file, which can be found at the root of the source code       *
 * distribution tree, or in https://www.hdfgroup.org/licenses.               *
 * If you do not have access to either file, you may request a copy from     *
 * help@hdfgroup.org.                                                        *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/*-------------------------------------------------------------------------
 *
 * Created:     H5Cmpio.c
 *              June 20 2015
 *              Quincey Koziol
 *
 * Purpose:     Functions in this file implement support for parallel I/O for
 *              generic cache code.
 *
 *-------------------------------------------------------------------------
 */

/****************/
/* Module Setup */
/****************/

#include "H5Cmodule.h" /* This source code file is part of the H5C module */
#define H5F_FRIEND     /*suppress error about including H5Fpkg      */

/***********/
/* Headers */
/***********/
#include "H5private.h"   /* Generic Functions                    */
#include "H5ACprivate.h" /* Metadata cache                       */
#include "H5Cpkg.h"      /* Cache                                */
#include "H5CXprivate.h" /* API Contexts                         */
#include "H5Eprivate.h"  /* Error handling                       */
#include "H5Fpkg.h"      /* Files                                */
#include "H5FDprivate.h" /* File drivers                         */
#include "H5MMprivate.h" /* Memory management                    */

#ifdef H5_HAVE_PARALLEL
/****************/
/* Local Macros */
/****************/
#define H5C_APPLY_CANDIDATE_LIST__DEBUG 0

/******************/
/* Local Typedefs */
/******************/

/********************/
/* Local Prototypes */
/********************/
static herr_t H5C__collective_write(H5F_t *f);
static herr_t H5C__flush_candidate_entries(H5F_t *f, unsigned entries_to_flush[H5C_RING_NTYPES],
                                           unsigned entries_to_clear[H5C_RING_NTYPES]);
static herr_t H5C__flush_candidates_in_ring(H5F_t *f, H5C_ring_t ring, unsigned entries_to_flush,
                                            unsigned entries_to_clear);

/*********************/
/* Package Variables */
/*********************/

/*****************************/
/* Library Private Variables */
/*****************************/

/*******************/
/* Local Variables */
/*******************/

/*-------------------------------------------------------------------------
 * Function:    H5C_apply_candidate_list
 *
 * Purpose:     Apply the supplied candidate list.
 *
 *              We used to do this by simply having each process write
 *              every mpi_size-th entry in the candidate list, starting
 *              at index mpi_rank, and mark all the others clean.
 *
 *              However, this can cause unnecessary contention in a file
 *              system by increasing the number of processes writing to
 *              adjacent locations in the HDF5 file.
 *
 *              To attempt to minimize this, we now arange matters such
 *              that each process writes n adjacent entries in the
 *              candidate list, and marks all others clean.  We must do
 *              this in such a fashion as to guarantee that each entry
 *              on the candidate list is written by exactly one process,
 *              and marked clean by all others.
 *
 *              To do this, first construct a table mapping mpi_rank
 *              to the index of the first entry in the candidate list to
 *              be written by the process of that mpi_rank, and then use
 *              the table to control which entries are written and which
 *              are marked as clean as a function of the mpi_rank.
 *
 *              Note that the table must be identical on all processes, as
 *              all see the same candidate list, mpi_size, and mpi_rank --
 *              the inputs used to construct the table.
 *
 *              We construct the table as follows.  Let:
 *
 *                      n = num_candidates / mpi_size;
 *
 *                      m = num_candidates % mpi_size;
 *
 *              Now allocate an array of integers of length mpi_size + 1,
 *              and call this array candidate_assignment_table.
 *
 *              Conceptually, if the number of candidates is a multiple
 *              of the mpi_size, we simply pass through the candidate list
 *              and assign n entries to each process to flush, with the
 *              index of the first entry to flush in the location in
 *              the candidate_assignment_table indicated by the mpi_rank
 *              of the process.
 *
 *              In the more common case in which the candidate list isn't
 *              isn't a multiple of the mpi_size, we pretend it is, and
 *              give num_candidates % mpi_size processes one extra entry
 *              each to make things work out.
 *
 *              Once the table is constructed, we determine the first and
 *              last entry this process is to flush as follows:
 *
 *              first_entry_to_flush = candidate_assignment_table[mpi_rank]
 *
 *              last_entry_to_flush =
 *                      candidate_assignment_table[mpi_rank + 1] - 1;
 *
 *              With these values determined, we simply scan through the
 *              candidate list, marking all entries in the range
 *              [first_entry_to_flush, last_entry_to_flush] for flush,
 *              and all others to be cleaned.
 *
 *              Finally, we scan the LRU from tail to head, flushing
 *              or marking clean the candidate entries as indicated.
 *              If necessary, we scan the pinned list as well.
 *
 *              Note that this function will fail if any protected or
 *              clean entries appear on the candidate list.
 *
 *              This function is used in managing sync points, and
 *              shouldn't be used elsewhere.
 *
 * Return:      Success:        SUCCEED
 *
 *              Failure:        FAIL
 *
 * Programmer:  John Mainzer
 *              3/17/10
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5C_apply_candidate_list(H5F_t *f, H5C_t *cache_ptr, unsigned num_candidates, haddr_t *candidates_list_ptr,
                         int mpi_rank, int mpi_size)
{
    unsigned           first_entry_to_flush;
    unsigned           last_entry_to_flush;
    unsigned           total_entries_to_clear     = 0;
    unsigned           total_entries_to_flush     = 0;
    unsigned          *candidate_assignment_table = NULL;
    unsigned           entries_to_flush[H5C_RING_NTYPES];
    unsigned           entries_to_clear[H5C_RING_NTYPES];
    haddr_t            addr;
    H5C_cache_entry_t *entry_ptr = NULL;
#if H5C_DO_SANITY_CHECKS
    haddr_t last_addr;
#endif /* H5C_DO_SANITY_CHECKS */
#if H5C_APPLY_CANDIDATE_LIST__DEBUG
    char tbl_buf[1024];
#endif /* H5C_APPLY_CANDIDATE_LIST__DEBUG */
    unsigned m, n;
    unsigned u;                   /* Local index variable */
    herr_t   ret_value = SUCCEED; /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    /* Sanity checks */
    HDassert(cache_ptr != NULL);
    HDassert(cache_ptr->magic == H5C__H5C_T_MAGIC);
    HDassert(num_candidates > 0);
    HDassert((!cache_ptr->slist_enabled) || (num_candidates <= cache_ptr->slist_len));
    HDassert(candidates_list_ptr != NULL);
    HDassert(0 <= mpi_rank);
    HDassert(mpi_rank < mpi_size);

    /* Initialize the entries_to_flush and entries_to_clear arrays */
    HDmemset(entries_to_flush, 0, sizeof(entries_to_flush));
    HDmemset(entries_to_clear, 0, sizeof(entries_to_clear));

#if H5C_APPLY_CANDIDATE_LIST__DEBUG
    HDfprintf(stdout, "%s:%d: setting up candidate assignment table.\n", __func__, mpi_rank);

    HDmemset(tbl_buf, 0, sizeof(tbl_buf));

    HDsnprintf(tbl_buf, sizeof(tbl_buf), "candidate list = ");
    for (u = 0; u < num_candidates; u++)
        HDsprintf(&(tbl_buf[HDstrlen(tbl_buf)]), " 0x%llx", (long long)(*(candidates_list_ptr + u)));
    HDsprintf(&(tbl_buf[HDstrlen(tbl_buf)]), "\n");

    HDfprintf(stdout, "%s", tbl_buf);
#endif /* H5C_APPLY_CANDIDATE_LIST__DEBUG */

    if (f->shared->coll_md_write) {
        /* Sanity check */
        HDassert(NULL == cache_ptr->coll_write_list);

        /* Create skip list of entries for collective write */
        if (NULL == (cache_ptr->coll_write_list = H5SL_create(H5SL_TYPE_HADDR, NULL)))
            HGOTO_ERROR(H5E_DATASET, H5E_CANTCREATE, FAIL, "can't create skip list for entries")
    } /* end if */

    n = num_candidates / (unsigned)mpi_size;
    m = num_candidates % (unsigned)mpi_size;

    if (NULL ==
        (candidate_assignment_table = (unsigned *)H5MM_malloc(sizeof(unsigned) * (size_t)(mpi_size + 1))))
        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL,
                    "memory allocation failed for candidate assignment table")

    candidate_assignment_table[0]        = 0;
    candidate_assignment_table[mpi_size] = num_candidates;

    if (m == 0) { /* mpi_size is an even divisor of num_candidates */
        for (u = 1; u < (unsigned)mpi_size; u++)
            candidate_assignment_table[u] = candidate_assignment_table[u - 1] + n;
    } /* end if */
    else {
        for (u = 1; u <= m; u++)
            candidate_assignment_table[u] = candidate_assignment_table[u - 1] + n + 1;

        if (num_candidates < (unsigned)mpi_size) {
            for (u = m + 1; u < (unsigned)mpi_size; u++)
                candidate_assignment_table[u] = num_candidates;
        } /* end if */
        else {
            for (u = m + 1; u < (unsigned)mpi_size; u++)
                candidate_assignment_table[u] = candidate_assignment_table[u - 1] + n;
        } /* end else */
    }     /* end else */
    HDassert((candidate_assignment_table[mpi_size - 1] + n) == num_candidates);

#if H5C_DO_SANITY_CHECKS
    /* Verify that the candidate assignment table has the expected form */
    for (u = 1; u < (unsigned)(mpi_size - 1); u++) {
        unsigned a, b;

        a = candidate_assignment_table[u] - candidate_assignment_table[u - 1];
        b = candidate_assignment_table[u + 1] - candidate_assignment_table[u];

        HDassert(n + 1 >= a);
        HDassert(a >= b);
        HDassert(b >= n);
    }
#endif /* H5C_DO_SANITY_CHECKS */

    first_entry_to_flush = candidate_assignment_table[mpi_rank];
    last_entry_to_flush  = candidate_assignment_table[mpi_rank + 1] - 1;

#if H5C_APPLY_CANDIDATE_LIST__DEBUG
    for (u = 0; u < 1024; u++)
        tbl_buf[u] = '\0';
    HDsnprintf(tbl_buf, sizeof(tbl_buf), "candidate assignment table = ");
    for (u = 0; u <= (unsigned)mpi_size; u++)
        HDsprintf(&(tbl_buf[HDstrlen(tbl_buf)]), " %u", candidate_assignment_table[u]);
    HDsprintf(&(tbl_buf[HDstrlen(tbl_buf)]), "\n");
    HDfprintf(stdout, "%s", tbl_buf);

    HDfprintf(stdout, "%s:%d: flush entries [%u, %u].\n", __func__, mpi_rank, first_entry_to_flush,
              last_entry_to_flush);

    HDfprintf(stdout, "%s:%d: marking entries.\n", __func__, mpi_rank);
#endif /* H5C_APPLY_CANDIDATE_LIST__DEBUG */

    for (u = 0; u < num_candidates; u++) {
        addr = candidates_list_ptr[u];
        HDassert(H5F_addr_defined(addr));

#if H5C_DO_SANITY_CHECKS
        if (u > 0) {
            if (last_addr == addr)
                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "duplicate entry in cleaned list")
            else if (last_addr > addr)
                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "candidate list not sorted")
        } /* end if */

        last_addr = addr;
#endif /* H5C_DO_SANITY_CHECKS */

        H5C__SEARCH_INDEX(cache_ptr, addr, entry_ptr, FAIL)
        if (entry_ptr == NULL)
            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "listed candidate entry not in cache?!?!?")
        if (!entry_ptr->is_dirty)
            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Listed entry not dirty?!?!?")
        if (entry_ptr->is_protected)
            /* For now at least, we can't deal with protected entries.
             * If we encounter one, scream and die.  If it becomes an
             * issue, we should be able to work around this.
             */
            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Listed entry is protected?!?!?")

        /* Sanity checks */
        HDassert(entry_ptr->magic == H5C__H5C_CACHE_ENTRY_T_MAGIC);
        HDassert(entry_ptr->ring >= H5C_RING_USER);
        HDassert(entry_ptr->ring <= H5C_RING_SB);
        HDassert(!entry_ptr->flush_immediately);
        HDassert(!entry_ptr->clear_on_unprotect);

        /* Determine whether the entry is to be cleared or flushed,
         * and mark it accordingly.  We will scan the protected and
         * pinned list shortly, and clear or flush according to these
         * markings.
         */
        if (u >= first_entry_to_flush && u <= last_entry_to_flush) {
            total_entries_to_flush++;
            entries_to_flush[entry_ptr->ring]++;
            entry_ptr->flush_immediately = TRUE;
        } /* end if */
        else {
            total_entries_to_clear++;
            entries_to_clear[entry_ptr->ring]++;
            entry_ptr->clear_on_unprotect = TRUE;
        } /* end else */

        /* Entries marked as collectively accessed and are in the
         * candidate list to clear from the cache have to be
         * removed from the coll list. This is OK since the
         * candidate list is collective and uniform across all
         * ranks.
         */
        if (entry_ptr->coll_access) {
            entry_ptr->coll_access = FALSE;
            H5C__REMOVE_FROM_COLL_LIST(cache_ptr, entry_ptr, FAIL)
        } /* end if */
    }     /* end for */

#if H5C_DO_SANITY_CHECKS
    m = 0;
    n = 0;
    for (u = 0; u < H5C_RING_NTYPES; u++) {
        m += entries_to_flush[u];
        n += entries_to_clear[u];
    } /* end if */

    HDassert((unsigned)m == total_entries_to_flush);
    HDassert(n == total_entries_to_clear);
#endif /* H5C_DO_SANITY_CHECKS */

#if H5C_APPLY_CANDIDATE_LIST__DEBUG
    HDfprintf(stdout, "%s:%d: num candidates/to clear/to flush = %u/%u/%u.\n", __func__, mpi_rank,
              num_candidates, total_entries_to_clear, total_entries_to_flush);
#endif /* H5C_APPLY_CANDIDATE_LIST__DEBUG */

    /* We have now marked all the entries on the candidate list for
     * either flush or clear -- now scan the LRU and the pinned list
     * for these entries and do the deed.  Do this via a call to
     * H5C__flush_candidate_entries().
     *
     * Note that we are doing things in this round about manner so as
     * to preserve the order of the LRU list to the best of our ability.
     * If we don't do this, my experiments indicate that we will have a
     * noticeably poorer hit ratio as a result.
     */
    if (H5C__flush_candidate_entries(f, entries_to_flush, entries_to_clear) < 0)
        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "flush candidates failed")

    /* If we've deferred writing to do it collectively, take care of that now */
    if (f->shared->coll_md_write) {
        /* Sanity check */
        HDassert(cache_ptr->coll_write_list);

        /* Write collective list */
        if (H5C__collective_write(f) < 0)
            HGOTO_ERROR(H5E_CACHE, H5E_WRITEERROR, FAIL, "can't write metadata collectively")
    } /* end if */

done:
    if (candidate_assignment_table != NULL)
        candidate_assignment_table = (unsigned *)H5MM_xfree((void *)candidate_assignment_table);
    if (cache_ptr->coll_write_list) {
        if (H5SL_close(cache_ptr->coll_write_list) < 0)
            HDONE_ERROR(H5E_CACHE, H5E_CANTFREE, FAIL, "failed to destroy skip list")
        cache_ptr->coll_write_list = NULL;
    } /* end if */

    FUNC_LEAVE_NOAPI(ret_value)
} /* H5C_apply_candidate_list() */

/*-------------------------------------------------------------------------
 *
 * Function:    H5C_construct_candidate_list__clean_cache
 *
 * Purpose:     Construct the list of entries that should be flushed to
 *              clean all entries in the cache.
 *
 *              This function is used in managing sync points, and
 *              shouldn't be used elsewhere.
 *
 * Return:      Success:        SUCCEED
 *
 *              Failure:        FAIL
 *
 * Programmer:  John Mainzer
 *              3/17/10
 *
 * Changes:     With the slist optimization, the slist is not maintained
 *              unless a flush is in progress.  Thus we can not longer use
 *              cache_ptr->slist_size to determine the total size of
 *              the entries we must insert in the candidate list.
 *
 *              To address this, we now use cache_ptr->dirty_index_size
 *              instead.
 *
 *                                              JRM -- 7/27/20
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5C_construct_candidate_list__clean_cache(H5C_t *cache_ptr)
{
    size_t space_needed;
    herr_t ret_value = SUCCEED; /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    HDassert(cache_ptr != NULL);
    HDassert(cache_ptr->magic == H5C__H5C_T_MAGIC);

    /* As a sanity check, set space needed to the dirty_index_size.  This
     * should be the sum total of the sizes of all the dirty entries
     * in the metadata cache.  Note that if the slist is enabled,
     * cache_ptr->slist_size should equal cache_ptr->dirty_index_size.
     */
    space_needed = cache_ptr->dirty_index_size;

    HDassert((!cache_ptr->slist_enabled) || (space_needed == cache_ptr->slist_size));

    /* Recall that while we shouldn't have any protected entries at this
     * point, it is possible that some dirty entries may reside on the
     * pinned list at this point.
     */
    HDassert(cache_ptr->dirty_index_size <= (cache_ptr->dLRU_list_size + cache_ptr->pel_size));
    HDassert((!cache_ptr->slist_enabled) ||
             (cache_ptr->slist_len <= (cache_ptr->dLRU_list_len + cache_ptr->pel_len)));

    if (space_needed > 0) { /* we have work to do */

        H5C_cache_entry_t *entry_ptr;
        unsigned           nominated_entries_count = 0;
        size_t             nominated_entries_size  = 0;
        haddr_t            nominated_addr;

        HDassert((!cache_ptr->slist_enabled) || (cache_ptr->slist_len > 0));

        /* Scan the dirty LRU list from tail forward and nominate sufficient
         * entries to free up the necessary space.
         */
        entry_ptr = cache_ptr->dLRU_tail_ptr;

        while ((nominated_entries_size < space_needed) &&
               ((!cache_ptr->slist_enabled) || (nominated_entries_count < cache_ptr->slist_len)) &&
               (entry_ptr != NULL)) {

            HDassert(!(entry_ptr->is_protected));
            HDassert(!(entry_ptr->is_read_only));
            HDassert(entry_ptr->ro_ref_count == 0);
            HDassert(entry_ptr->is_dirty);
            HDassert((!cache_ptr->slist_enabled) || (entry_ptr->in_slist));

            nominated_addr = entry_ptr->addr;

            if (H5AC_add_candidate((H5AC_t *)cache_ptr, nominated_addr) < 0)

                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "H5AC_add_candidate() failed")

            nominated_entries_size += entry_ptr->size;
            nominated_entries_count++;
            entry_ptr = entry_ptr->aux_prev;

        } /* end while */

        HDassert(entry_ptr == NULL);

        /* it is possible that there are some dirty entries on the
         * protected entry list as well -- scan it too if necessary
         */
        entry_ptr = cache_ptr->pel_head_ptr;

        while ((nominated_entries_size < space_needed) &&
               ((!cache_ptr->slist_enabled) || (nominated_entries_count < cache_ptr->slist_len)) &&
               (entry_ptr != NULL)) {

            if (entry_ptr->is_dirty) {

                HDassert(!(entry_ptr->is_protected));
                HDassert(!(entry_ptr->is_read_only));
                HDassert(entry_ptr->ro_ref_count == 0);
                HDassert(entry_ptr->is_dirty);
                HDassert(entry_ptr->in_slist);

                nominated_addr = entry_ptr->addr;

                if (H5AC_add_candidate((H5AC_t *)cache_ptr, nominated_addr) < 0)

                    HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "H5AC_add_candidate() failed")

                nominated_entries_size += entry_ptr->size;
                nominated_entries_count++;

            } /* end if */

            entry_ptr = entry_ptr->next;

        } /* end while */

        HDassert((!cache_ptr->slist_enabled) || (nominated_entries_count == cache_ptr->slist_len));
        HDassert(nominated_entries_size == space_needed);

    } /* end if */

done:

    FUNC_LEAVE_NOAPI(ret_value)

} /* H5C_construct_candidate_list__clean_cache() */

/*-------------------------------------------------------------------------
 * Function:    H5C_construct_candidate_list__min_clean
 *
 * Purpose:     Construct the list of entries that should be flushed to
 *              get the cache back within its min clean constraints.
 *
 *              This function is used in managing sync points, and
 *              shouldn't be used elsewhere.
 *
 * Return:      Success:        SUCCEED
 *
 *              Failure:        FAIL
 *
 * Programmer:  John Mainzer
 *              3/17/10
 *
 * Changes:     With the slist optimization, the slist is not maintained
 *              unless a flush is in progress.  Updated sanity checks to
 *              reflect this.
 *
 *                                              JRM -- 7/27/20
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5C_construct_candidate_list__min_clean(H5C_t *cache_ptr)
{
    size_t space_needed = 0;
    herr_t ret_value    = SUCCEED; /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    HDassert(cache_ptr != NULL);
    HDassert(cache_ptr->magic == H5C__H5C_T_MAGIC);

    /* compute the number of bytes (if any) that must be flushed to get the
     * cache back within its min clean constraints.
     */
    if (cache_ptr->max_cache_size > cache_ptr->index_size) {

        if (((cache_ptr->max_cache_size - cache_ptr->index_size) + cache_ptr->cLRU_list_size) >=
            cache_ptr->min_clean_size) {

            space_needed = 0;
        }
        else {

            space_needed = cache_ptr->min_clean_size -
                           ((cache_ptr->max_cache_size - cache_ptr->index_size) + cache_ptr->cLRU_list_size);
        }
    } /* end if */
    else {

        if (cache_ptr->min_clean_size <= cache_ptr->cLRU_list_size) {

            space_needed = 0;
        }
        else {

            space_needed = cache_ptr->min_clean_size - cache_ptr->cLRU_list_size;
        }
    } /* end else */

    if (space_needed > 0) { /* we have work to do */

        H5C_cache_entry_t *entry_ptr;
        unsigned           nominated_entries_count = 0;
        size_t             nominated_entries_size  = 0;

        HDassert((!cache_ptr->slist_enabled) || (cache_ptr->slist_len > 0));

        /* Scan the dirty LRU list from tail forward and nominate sufficient
         * entries to free up the necessary space.
         */
        entry_ptr = cache_ptr->dLRU_tail_ptr;

        while ((nominated_entries_size < space_needed) &&
               ((!cache_ptr->slist_enabled) || (nominated_entries_count < cache_ptr->slist_len)) &&
               (entry_ptr != NULL) && (!entry_ptr->flush_me_last)) {

            haddr_t nominated_addr;

            HDassert(!(entry_ptr->is_protected));
            HDassert(!(entry_ptr->is_read_only));
            HDassert(entry_ptr->ro_ref_count == 0);
            HDassert(entry_ptr->is_dirty);
            HDassert((!cache_ptr->slist_enabled) || (entry_ptr->in_slist));

            nominated_addr = entry_ptr->addr;

            if (H5AC_add_candidate((H5AC_t *)cache_ptr, nominated_addr) < 0)

                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "H5AC_add_candidate() failed")

            nominated_entries_size += entry_ptr->size;
            nominated_entries_count++;
            entry_ptr = entry_ptr->aux_prev;

        } /* end while */

        HDassert((!cache_ptr->slist_enabled) || (nominated_entries_count <= cache_ptr->slist_len));
        HDassert(nominated_entries_size <= cache_ptr->dirty_index_size);
        HDassert(nominated_entries_size >= space_needed);
    } /* end if */

done:
    FUNC_LEAVE_NOAPI(ret_value)
} /* H5C_construct_candidate_list__min_clean() */

/*-------------------------------------------------------------------------
 *
 * Function:    H5C_mark_entries_as_clean
 *
 * Purpose:     When the H5C code is used to implement the metadata caches
 *              in PHDF5, only the cache with MPI_rank 0 is allowed to
 *              actually write entries to disk -- all other caches must
 *              retain dirty entries until they are advised that the
 *              entries are clean.
 *
 *              This function exists to allow the H5C code to receive these
 *              notifications.
 *
 *              The function receives a list of entry base addresses
 *              which must refer to dirty entries in the cache.  If any
 *              of the entries are either clean or don't exist, the
 *              function flags an error.
 *
 *              The function scans the list of entries and flushes all
 *              those that are currently unprotected with the
 *              H5C__FLUSH_CLEAR_ONLY_FLAG.  Those that are currently
 *              protected are flagged for clearing when they are
 *              unprotected.
 *
 * Return:      Non-negative on success/Negative on failure
 *
 * Programmer:  John Mainzer
 *              7/5/05
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5C_mark_entries_as_clean(H5F_t *f, unsigned ce_array_len, haddr_t *ce_array_ptr)
{
    H5C_t   *cache_ptr;
    unsigned entries_cleared;
    unsigned pinned_entries_cleared;
    hbool_t  progress;
    unsigned entries_examined;
    unsigned initial_list_len;
    haddr_t  addr;
    unsigned pinned_entries_marked = 0;
#if H5C_DO_SANITY_CHECKS
    unsigned protected_entries_marked = 0;
    unsigned other_entries_marked     = 0;
    haddr_t  last_addr;
#endif /* H5C_DO_SANITY_CHECKS */
    H5C_cache_entry_t *clear_ptr = NULL;
    H5C_cache_entry_t *entry_ptr = NULL;
    unsigned           u;
    herr_t             ret_value = SUCCEED; /* Return value */

    FUNC_ENTER_NOAPI(FAIL)

    HDassert(f);
    HDassert(f->shared);
    cache_ptr = f->shared->cache;
    HDassert(cache_ptr);
    HDassert(cache_ptr->magic == H5C__H5C_T_MAGIC);

    HDassert(ce_array_len > 0);
    HDassert(ce_array_ptr != NULL);

#if H5C_DO_EXTREME_SANITY_CHECKS
    if (H5C_validate_protected_entry_list(cache_ptr) < 0 || H5C_validate_pinned_entry_list(cache_ptr) < 0 ||
        H5C_validate_lru_list(cache_ptr) < 0)
        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "an extreme sanity check failed on entry")
#endif /* H5C_DO_EXTREME_SANITY_CHECKS */

    for (u = 0; u < ce_array_len; u++) {
        addr = ce_array_ptr[u];

#if H5C_DO_SANITY_CHECKS
        if (u == 0)
            last_addr = addr;
        else {
            if (last_addr == addr)
                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Duplicate entry in cleaned list")
            if (last_addr > addr)
                HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "cleaned list not sorted")
        } /* end else */

#if H5C_DO_EXTREME_SANITY_CHECKS
        if (H5C_validate_protected_entry_list(cache_ptr) < 0 ||
            H5C_validate_pinned_entry_list(cache_ptr) < 0 || H5C_validate_lru_list(cache_ptr) < 0)
            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "an extreme sanity check failed in for loop")
#endif /* H5C_DO_EXTREME_SANITY_CHECKS */
#endif /* H5C_DO_SANITY_CHECKS */

        HDassert(H5F_addr_defined(addr));

        H5C__SEARCH_INDEX(cache_ptr, addr, entry_ptr, FAIL)

        if (entry_ptr == NULL) {
#if H5C_DO_SANITY_CHECKS
            HDfprintf(stdout, "H5C_mark_entries_as_clean: entry[%u] = %" PRIuHADDR " not in cache.\n", u,
                      addr);
#endif /* H5C_DO_SANITY_CHECKS */
            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Listed entry not in cache?!?!?")
        } /* end if */
        else if (!entry_ptr->is_dirty) {
#if H5C_DO_SANITY_CHECKS
            HDfprintf(stdout, "H5C_mark_entries_as_clean: entry %" PRIuHADDR " is not dirty!?!\n", addr);
#endif /* H5C_DO_SANITY_CHECKS */
            HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "Listed entry not dirty?!?!?")
        } /* end else-if */
        else {
            /* Mark the entry to be cleared on unprotect.  We will
             * scan the LRU list shortly, and clear all those entries
             * not currently protected.
             */

            /* Make sure first that we clear the collective flag from
               it so it can be cleared */
            if (TRUE == entry_ptr->coll_access) {
                entry_ptr->coll_access = FALSE;
                H5C__REMOVE_FROM_COLL_LIST(cache_ptr, entry_ptr, FAIL)
            } /* end if */

            entry_ptr->clear_on_unprotect = TRUE;
            if (entry_ptr->is_pinned)
                pinned_entries_marked++;
#if H5C_DO_SANITY_CHECKS
            else if (entry_ptr->is_protected)
                protected_entries_marked++;
            else
                other_entries_marked++;
#endif /* H5C_DO_SANITY_CHECKS */
        }
    }

    /* Scan through the LRU list from back to front, and flush the
     * entries whose clear_on_unprotect flags are set.  Observe that
     * any protected entries will not be on the LRU, and therefore
     * will not be flushed at this time.
     *
     * Note that unlike H5C_apply_candidate_list(),
     * H5C_mark_entries_as_clean() makes all its calls to
     * H5C__flush_single_entry() with the H5C__FLUSH_CLEAR_ONLY_FLAG
     * set.  As a result, the pre_serialize() and serialize calls are
     * not made.
     *
     * This then implies that (assuming such actions were
     * permitted in the parallel case) no loads, dirties,
     * resizes, or removals of other entries can occur as
     * a side effect of the flush.  Hence, there is no need
     * for the checks for entry removal / status change
     * that I ported to H5C_apply_candidate_list().
     *
     * However, if (in addition to allowing such operations
     * in the parallel case), we allow such operations outside
     * of the pre_serialize / serialize routines, this may
     * cease to be the case -- requiring a review of this
     * point.
     *                                  JRM -- 4/7/15
     */
    entries_cleared  = 0;
    entries_examined = 0;
    initial_list_len = cache_ptr->LRU_list_len;
    entry_ptr        = cache_ptr->LRU_tail_ptr;
    while (entry_ptr != NULL && entries_examined <= initial_list_len && entries_cleared < ce_array_len) {
        if (entry_ptr->clear_on_unprotect) {
            entry_ptr->clear_on_unprotect = FALSE;
            clear_ptr                     = entry_ptr;
            entry_ptr                     = entry_ptr->prev;
            entries_cleared++;

            if (H5C__flush_single_entry(f, clear_ptr,
                                        (H5C__FLUSH_CLEAR_ONLY_FLAG | H5C__GENERATE_IMAGE_FLAG |
                                         H5C__UPDATE_PAGE_BUFFER_FLAG)) < 0)
                HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "can't clear entry")
        } /* end if */
        else
            entry_ptr = entry_ptr->prev;
        entries_examined++;
    } /* end while */

#if H5C_DO_SANITY_CHECKS
    HDassert(entries_cleared == other_entries_marked);
#endif /* H5C_DO_SANITY_CHECKS */

    /* It is also possible that some of the cleared entries are on the
     * pinned list.  Must scan that also.
     */
    pinned_entries_cleared = 0;
    progress               = TRUE;
    while ((pinned_entries_cleared < pinned_entries_marked) && progress) {
        progress  = FALSE;
        entry_ptr = cache_ptr->pel_head_ptr;
        while (entry_ptr != NULL) {
            if (entry_ptr->clear_on_unprotect && entry_ptr->flush_dep_ndirty_children == 0) {
                entry_ptr->clear_on_unprotect = FALSE;
                clear_ptr                     = entry_ptr;
                entry_ptr                     = entry_ptr->next;
                entries_cleared++;
                pinned_entries_cleared++;
                progress = TRUE;

                if (H5C__flush_single_entry(f, clear_ptr,
                                            (H5C__FLUSH_CLEAR_ONLY_FLAG | H5C__GENERATE_IMAGE_FLAG |
                                             H5C__UPDATE_PAGE_BUFFER_FLAG)) < 0)
                    HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "can't clear entry")
            } /* end if */
            else
                entry_ptr = entry_ptr->next;
        } /* end while */
    }     /* end while */

#if H5C_DO_SANITY_CHECKS
    HDassert(entries_cleared == pinned_entries_marked + other_entries_marked);
    HDassert(entries_cleared + protected_entries_marked == ce_array_len);
#endif /* H5C_DO_SANITY_CHECKS */

    HDassert((entries_cleared == ce_array_len) || ((ce_array_len - entries_cleared) <= cache_ptr->pl_len));

#if H5C_DO_SANITY_CHECKS
    u         = 0;
    entry_ptr = cache_ptr->pl_head_ptr;
    while (entry_ptr != NULL) {
        if (entry_ptr->clear_on_unprotect) {

            u++;
        }
        entry_ptr = entry_ptr->next;
    }
    HDassert((entries_cleared + u) == ce_array_len);
#endif /* H5C_DO_SANITY_CHECKS */

done:
#if H5C_DO_EXTREME_SANITY_CHECKS
    if (H5C_validate_protected_entry_list(cache_ptr) < 0 || H5C_validate_pinned_entry_list(cache_ptr) < 0 ||
        H5C_validate_lru_list(cache_ptr) < 0)
        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "an extreme sanity check failed on exit")
#endif /* H5C_DO_EXTREME_SANITY_CHECKS */

    FUNC_LEAVE_NOAPI(ret_value)
} /* H5C_mark_entries_as_clean() */

/*-------------------------------------------------------------------------
 *
 * Function:    H5C_clear_coll_entries
 *
 * Purpose:     Clear half or the entire list of collective entries and
 *              mark them as independent.
 *
 * Return:      FAIL if error is detected, SUCCEED otherwise.
 *
 * Programmer:  Mohamad Chaarawi
 *              April, 2015
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5C_clear_coll_entries(H5C_t *cache_ptr, hbool_t partial)
{
    uint32_t           clear_cnt;
    H5C_cache_entry_t *entry_ptr = NULL;
    herr_t             ret_value = SUCCEED;

#if H5C_DO_SANITY_CHECKS
    FUNC_ENTER_NOAPI_NOINIT
#else
    FUNC_ENTER_NOAPI_NOINIT_NOERR
#endif

    entry_ptr = cache_ptr->coll_tail_ptr;
    clear_cnt = (partial ? cache_ptr->coll_list_len / 2 : cache_ptr->coll_list_len);
    while (entry_ptr && clear_cnt > 0) {
        H5C_cache_entry_t *prev_ptr = entry_ptr->coll_prev;

        /* Sanity check */
        HDassert(entry_ptr->coll_access);

        /* Mark entry as independent */
        entry_ptr->coll_access = FALSE;
        H5C__REMOVE_FROM_COLL_LIST(cache_ptr, entry_ptr, FAIL)

        /* Decrement entry count */
        clear_cnt--;

        /* Advance to next entry */
        entry_ptr = prev_ptr;
    } /* end while */

#if H5C_DO_SANITY_CHECKS
done:
#endif /* H5C_DO_SANITY_CHECKS */
    FUNC_LEAVE_NOAPI(ret_value)
} /* H5C_clear_coll_entries */

/*-------------------------------------------------------------------------
 *
 * Function:    H5C__collective_write
 *
 * Purpose:     Perform a collective write of a list of metadata entries.
 *
 * Return:      FAIL if error is detected, SUCCEED otherwise.
 *
 * Programmer:  Mohamad Chaarawi
 *              February, 2016
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5C__collective_write(H5F_t *f)
{
    H5AC_t          *cache_ptr;
    H5FD_mpio_xfer_t orig_xfer_mode = H5FD_MPIO_COLLECTIVE;
    const void     **bufs           = NULL;
    H5FD_mem_t      *types          = NULL;
    haddr_t         *addrs          = NULL;
    size_t          *sizes          = NULL;
    uint32_t         count32;
    size_t           count;
    herr_t           ret_value = SUCCEED;

    FUNC_ENTER_PACKAGE

    /* Sanity checks */
    HDassert(f != NULL);
    cache_ptr = f->shared->cache;
    HDassert(cache_ptr != NULL);
    HDassert(cache_ptr->coll_write_list != NULL);

    /* Get original transfer mode */
    if (H5CX_get_io_xfer_mode(&orig_xfer_mode) < 0)
        HGOTO_ERROR(H5E_CACHE, H5E_CANTGET, FAIL, "can't get MPI-I/O transfer mode")

    /* Set transfer mode */
    if (H5CX_set_io_xfer_mode(H5FD_MPIO_COLLECTIVE) < 0)
        HGOTO_ERROR(H5E_CACHE, H5E_CANTSET, FAIL, "can't set MPI-I/O transfer mode")

    /* Get number of entries in collective write list */
    count = H5SL_count(cache_ptr->coll_write_list);
    H5_CHECKED_ASSIGN(count32, uint32_t, count, size_t);

    if (count > 0) {
        H5SL_node_t       *node;
        H5C_cache_entry_t *entry_ptr;
        void              *base_buf;
        int                i;

        if (NULL == (addrs = H5MM_malloc(count * sizeof(*addrs))))
            HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "couldn't allocate address array")
        if (NULL == (sizes = H5MM_malloc(count * sizeof(*sizes))))
            HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "couldn't allocate sizes array")
        if (NULL == (bufs = H5MM_malloc(count * sizeof(*bufs))))
            HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "couldn't allocate buffers array")
        if (NULL == (types = H5MM_malloc(count * sizeof(*types))))
            HGOTO_ERROR(H5E_CACHE, H5E_CANTALLOC, FAIL, "couldn't allocate types array")

        /* Fill arrays */
        node = H5SL_first(cache_ptr->coll_write_list);
        HDassert(node);
        if (NULL == (entry_ptr = (H5C_cache_entry_t *)H5SL_item(node)))
            HGOTO_ERROR(H5E_CACHE, H5E_NOTFOUND, FAIL, "can't retrieve skip list item")

        /* Set up initial array position & buffer base address */
        HDassert(entry_ptr->type);
        base_buf = entry_ptr->image_ptr;
        addrs[0] = entry_ptr->addr;
        sizes[0] = entry_ptr->size;
        bufs[0]  = base_buf;
        types[0] = entry_ptr->type->mem_type;

        node = H5SL_next(node);
        i    = 1;
        while (node) {
            if (NULL == (entry_ptr = (H5C_cache_entry_t *)H5SL_item(node)))
                HGOTO_ERROR(H5E_CACHE, H5E_NOTFOUND, FAIL, "can't retrieve skip list item")

            /* Set up array position */
            HDassert(entry_ptr->type);
            addrs[i] = entry_ptr->addr;
            sizes[i] = entry_ptr->size;
            bufs[i]  = entry_ptr->image_ptr;
            types[i] = entry_ptr->type->mem_type;

            /* Advance to next node & array location */
            node = H5SL_next(node);
            i++;
        } /* end while */
    }     /* end if */

    /* Pass buf type, file type to the file driver */
    if (H5CX_set_mpi_coll_datatypes(MPI_BYTE, MPI_BYTE) < 0)
        HGOTO_ERROR(H5E_CACHE, H5E_CANTSET, FAIL, "can't set MPI-I/O properties")

    /* Make vector write call */
    if (H5F_shared_vector_write(H5F_SHARED(f), count32, types, addrs, sizes, bufs) < 0)
        HGOTO_ERROR(H5E_CACHE, H5E_WRITEERROR, FAIL, "unable to write entries")

done:
    H5MM_xfree(types);
    H5MM_xfree(bufs);
    H5MM_xfree(sizes);
    H5MM_xfree(addrs);

    /* Reset transfer mode in API context, if changed */
    if (orig_xfer_mode != H5FD_MPIO_COLLECTIVE)
        if (H5CX_set_io_xfer_mode(orig_xfer_mode) < 0)
            HDONE_ERROR(H5E_CACHE, H5E_CANTSET, FAIL, "can't set MPI-I/O transfer mode")

    FUNC_LEAVE_NOAPI(ret_value);
} /* end H5C__collective_write() */

/*-------------------------------------------------------------------------
 * Function:    H5C__flush_candidate_entries
 *
 * Purpose:     Flush or clear (as indicated) the candidate entries that
 *              have been marked in the metadata cache.  In so doing,
 *              observe rings and flush dependencies.
 *
 *              Note that this function presumes that:
 *
 *              1) no candidate entries are protected,
 *
 *              2) all candidate entries are dirty, and
 *
 *              3) if a candidate entry has a dirty flush dependency
 *                 child, that child is also a candidate entry.
 *
 *              The function will fail if any of these preconditions are
 *              not met.
 *
 *              Candidate entries are marked by setting either the
 *              flush_immediately or the clear_on_unprotect flags in the
 *              cache entry (but not both).  Entries marked flush_immediately
 *              will be flushed, those marked clear_on_unprotect will be
 *              cleared.
 *
 *              Note that this function is a modified version of
 *              H5C_flush_cache() -- any changes there may need to be
 *              reflected here and vice versa.
 *
 * Return:      Non-negative on success/Negative on failure.
 *
 * Programmer:  John Mainzer
 *              2/10/17
 *
 * Changes:     None.
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5C__flush_candidate_entries(H5F_t *f, unsigned entries_to_flush[H5C_RING_NTYPES],
                             unsigned entries_to_clear[H5C_RING_NTYPES])
{
#if H5C_DO_SANITY_CHECKS
    int      i;
    uint32_t index_len        = 0;
    size_t   index_size       = (size_t)0;
    size_t   clean_index_size = (size_t)0;
    size_t   dirty_index_size = (size_t)0;
    size_t   slist_size       = (size_t)0;
    uint32_t slist_len        = 0;
#endif /* H5C_DO_SANITY_CHECKS */
    H5C_ring_t ring;
    H5C_t     *cache_ptr;
    herr_t     ret_value = SUCCEED;

    FUNC_ENTER_PACKAGE

    HDassert(f);
    HDassert(f->shared);

    cache_ptr = f->shared->cache;

    HDassert(cache_ptr);
    HDassert(cache_ptr->magic == H5C__H5C_T_MAGIC);
    HDassert(cache_ptr->slist_ptr);

    HDassert(entries_to_flush[H5C_RING_UNDEFINED] == 0);
    HDassert(entries_to_clear[H5C_RING_UNDEFINED] == 0);

#if H5C_DO_SANITY_CHECKS
    HDassert(cache_ptr->index_ring_len[H5C_RING_UNDEFINED] == 0);
    HDassert(cache_ptr->index_ring_size[H5C_RING_UNDEFINED] == (size_t)0);
    HDassert(cache_ptr->clean_index_ring_size[H5C_RING_UNDEFINED] == (size_t)0);
    HDassert(cache_ptr->dirty_index_ring_size[H5C_RING_UNDEFINED] == (size_t)0);
    HDassert(cache_ptr->slist_ring_len[H5C_RING_UNDEFINED] == 0);
    HDassert(cache_ptr->slist_ring_size[H5C_RING_UNDEFINED] == (size_t)0);

    for (i = H5C_RING_USER; i < H5C_RING_NTYPES; i++) {
        index_len += cache_ptr->index_ring_len[i];
        index_size += cache_ptr->index_ring_size[i];
        clean_index_size += cache_ptr->clean_index_ring_size[i];
        dirty_index_size += cache_ptr->dirty_index_ring_size[i];

        slist_len += cache_ptr->slist_ring_len[i];
        slist_size += cache_ptr->slist_ring_size[i];
    } /* end for */

    HDassert(cache_ptr->index_len == index_len);
    HDassert(cache_ptr->index_size == index_size);
    HDassert(cache_ptr->clean_index_size == clean_index_size);
    HDassert(cache_ptr->dirty_index_size == dirty_index_size);
    HDassert(cache_ptr->slist_len == slist_len);
    HDassert(cache_ptr->slist_size == slist_size);
#endif /* H5C_DO_SANITY_CHECKS */

#if H5C_DO_EXTREME_SANITY_CHECKS
    if (H5C_validate_protected_entry_list(cache_ptr) < 0 || H5C_validate_pinned_entry_list(cache_ptr) < 0 ||
        H5C_validate_lru_list(cache_ptr) < 0)
        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "an extreme sanity check failed on entry")
#endif /* H5C_DO_EXTREME_SANITY_CHECKS */

    cache_ptr->flush_in_progress = TRUE;

    /* flush each ring, starting from the outermost ring and
     * working inward.
     */
    ring = H5C_RING_USER;
    while (ring < H5C_RING_NTYPES) {
        if (H5C__flush_candidates_in_ring(f, ring, entries_to_flush[ring], entries_to_clear[ring]) < 0)
            HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "flush candidates in ring failed")

        ring++;
    } /* end while */

done:
    cache_ptr->flush_in_progress = FALSE;

    FUNC_LEAVE_NOAPI(ret_value)
} /* H5C__flush_candidate_entries() */

/*-------------------------------------------------------------------------
 * Function:    H5C__flush_candidates_in_ring
 *
 * Purpose:     Flush or clear (as indicated) the candidate entries
 *              contained in the specified cache and ring.  All candidate
 *              entries in rings outside the specified ring must have been
 *              flushed (or cleared) on entry.
 *
 *              Note that this function presumes that:
 *
 *              1) no candidate entries are protected,
 *
 *              2) all candidate entries are dirty, and
 *
 *              3) if a candidate entry has a dirty flush dependency
 *                 child, that child is also a candidate entry.
 *
 *              The function will fail if any of these preconditions are
 *              not met.
 *
 *              Candidate entries are marked by setting either the
 *              flush_immediately or the clear_on_unprotect flags in the
 *              cache entry (but not both).  Entries marked flush_immediately
 *              will be flushed, those marked clear_on_unprotect will be
 *              cleared.
 *
 *              Candidate entries residing in the LRU must be flushed
 *              (or cleared) in LRU order to avoid performance issues.
 *
 * Return:      Non-negative on success/Negative on failure.
 *
 * Programmer:  John Mainzer
 *              2/10/17
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5C__flush_candidates_in_ring(H5F_t *f, H5C_ring_t ring, unsigned entries_to_flush, unsigned entries_to_clear)
{
    H5C_t   *cache_ptr;
    hbool_t  progress;
    hbool_t  restart_scan    = FALSE;
    unsigned entries_flushed = 0;
    unsigned entries_cleared = 0;
#if H5C_DO_SANITY_CHECKS
    unsigned init_index_len;
#endif /* H5C_DO_SANITY_CHECKS */
    unsigned clear_flags =
        H5C__FLUSH_CLEAR_ONLY_FLAG | H5C__GENERATE_IMAGE_FLAG | H5C__UPDATE_PAGE_BUFFER_FLAG;
    unsigned           flush_flags = H5C__NO_FLAGS_SET;
    unsigned           op_flags;
    H5C_cache_entry_t *op_ptr;
    H5C_cache_entry_t *entry_ptr;
    herr_t             ret_value = SUCCEED;

    FUNC_ENTER_PACKAGE

    /* Sanity checks */
    HDassert(f);
    HDassert(f->shared);
    cache_ptr = f->shared->cache;
    HDassert(cache_ptr);
    HDassert(cache_ptr->magic == H5C__H5C_T_MAGIC);
    HDassert(cache_ptr->slist_ptr);
    HDassert(ring > H5C_RING_UNDEFINED);
    HDassert(ring < H5C_RING_NTYPES);

#if H5C_DO_EXTREME_SANITY_CHECKS
    if ((H5C_validate_protected_entry_list(cache_ptr) < 0) ||
        (H5C_validate_pinned_entry_list(cache_ptr) < 0) || (H5C_validate_lru_list(cache_ptr) < 0))
        HGOTO_ERROR(H5E_CACHE, H5E_SYSTEM, FAIL, "an extreme sanity check failed on entry")
#endif /* H5C_DO_EXTREME_SANITY_CHECKS */

#if H5C_DO_SANITY_CHECKS
    /* index len should not change */
    init_index_len = cache_ptr->index_len;
#endif /* H5C_DO_SANITY_CHECKS */

    /* Examine entries in the LRU list, and flush or clear all entries
     * so marked in the target ring.
     *
     * With the current implementation of flush dependencies, no entry
     * in the LRU can have flush dependency children -- thus one pass
     * through the LRU will be sufficient.
     *
     * It is possible that this will change -- hence the assertion.
     */
    restart_scan = FALSE;
    entry_ptr    = cache_ptr->LRU_tail_ptr;
    while (((entries_flushed < entries_to_flush) || (entries_cleared < entries_to_clear)) &&
           (entry_ptr != NULL)) {
        hbool_t            prev_is_dirty = FALSE;
        H5C_cache_entry_t *next_ptr;

        /* Entries in the LRU must not have flush dependency children */
        HDassert(entry_ptr->flush_dep_nchildren == 0);

        /* Remember dirty state of entry to advance to */
        if (entry_ptr->prev != NULL)
            prev_is_dirty = entry_ptr->prev->is_dirty;

        /* If the entry is in the ring */
        if (entry_ptr->ring == ring) {
            /* If this process needs to clear this entry. */
            if (entry_ptr->clear_on_unprotect) {
                HDassert(entry_ptr->is_dirty);

                /* Set entry and flags for operation */
                op_ptr   = entry_ptr;
                op_flags = clear_flags;

                /* Set next entry appropriately */
                next_ptr = entry_ptr->next;

                /* Reset entry flag */
                entry_ptr->clear_on_unprotect = FALSE;
                entries_cleared++;
            } /* end if */
            else if (entry_ptr->flush_immediately) {
                HDassert(entry_ptr->is_dirty);

                /* Set entry and flags for operation */
                op_ptr   = entry_ptr;
                op_flags = flush_flags;

                /* Set next entry appropriately */
                next_ptr = entry_ptr->next;

                /* Reset entry flag */
                entry_ptr->flush_immediately = FALSE;
                entries_flushed++;
            } /* end else-if */
            else {
                /* No operation for this entry */
                op_ptr = NULL;

                /* Set next entry appropriately */
                next_ptr = entry_ptr;
            } /* end else */

            /* Advance to next entry */
            entry_ptr = entry_ptr->prev;

            /* Check for operation */
            if (op_ptr) {
                /* reset entries_removed_counter and
                 * last_entry_removed_ptr prior to the call to
                 * H5C__flush_single_entry() so that we can spot
                 * unexpected removals of entries from the cache,
                 * and set the restart_scan flag if proceeding
                 * would be likely to cause us to scan an entry
                 * that is no longer in the cache.
                 *
                 * Note that as of this writing, this
                 * case cannot occur in the parallel case.
                 *
                 * Note also that there is no test code to verify
                 * that this code actually works (although similar code
                 * in the serial version exists and is tested).
                 */
                cache_ptr->entries_removed_counter = 0;
                cache_ptr->last_entry_removed_ptr  = NULL;

                if (H5C__flush_single_entry(f, op_ptr, op_flags) < 0)
                    HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "can't flush entry")

                if (cache_ptr->entries_removed_counter != 0 || cache_ptr->last_entry_removed_ptr != NULL)
                    restart_scan = TRUE;
            } /* end if */
        }     /* end if */
        else {
            /* Remember "next" pointer (after advancing entries) */
            next_ptr = entry_ptr;

            /* Advance to next entry */
            entry_ptr = entry_ptr->prev;
        } /* end else */

        /* Check for restarts, etc. */
        if ((entry_ptr != NULL) &&
            (restart_scan || (entry_ptr->is_dirty != prev_is_dirty) || (entry_ptr->next != next_ptr) ||
             entry_ptr->is_protected || entry_ptr->is_pinned)) {

            /* Something has happened to the LRU -- start over
             * from the tail.
             *
             * Recall that this code should be un-reachable at present,
             * as all the operations by entries on flush that could cause
             * it to be reachable are disallowed in the parallel case at
             * present.  Hence the following assertion which should be
             * removed if the above changes.
             */
            HDassert(!restart_scan);
            HDassert(entry_ptr->is_dirty == prev_is_dirty);
            HDassert(entry_ptr->next == next_ptr);
            HDassert(!entry_ptr->is_protected);
            HDassert(!entry_ptr->is_pinned);

            HDassert(FALSE); /* see comment above */

            restart_scan = FALSE;
            entry_ptr    = cache_ptr->LRU_tail_ptr;

            H5C__UPDATE_STATS_FOR_LRU_SCAN_RESTART(cache_ptr)
        } /* end if */
    }     /* end while */

    /* It is also possible that some of the cleared entries are on the
     * pinned list.  Must scan that also.
     *
     * Observe that in the case of the pinned entry list, most of the
     * entries will have flush dependency children.  As entries with
     * flush dependency children may not be flushed until all of their
     * children are clean, multiple passes throguh the pinned entry list
     * may be required.
     *
     * WARNING:
     *
     *  As we now allow unpinning, and removal of other entries as a side
     *  effect of flushing an entry, it is possible that the next entry
     *  in a PEL scan could either be no longer pinned, or no longer in
     *  the cache by the time we get to it.
     *
     *  At present, this should not be possible in this case, as we disallow
     *  such operations in the parallel version of the library.  However,
     *  this may change, and to that end, I have included code to detect
     *  such changes and cause this function to fail if they are detected.
     */
    progress = TRUE;
    while (progress && ((entries_flushed < entries_to_flush) || (entries_cleared < entries_to_clear))) {
        progress  = FALSE;
        entry_ptr = cache_ptr->pel_head_ptr;
        while ((entry_ptr != NULL) &&
               ((entries_flushed < entries_to_flush) || (entries_cleared < entries_to_clear))) {
            H5C_cache_entry_t *prev_ptr;
            hbool_t            next_is_dirty = FALSE;

            HDassert(entry_ptr->is_pinned);

            /* Remember dirty state of entry to advance to */
            if (entry_ptr->next != NULL)
                next_is_dirty = entry_ptr->next->is_dirty;

            if (entry_ptr->ring == ring && entry_ptr->flush_dep_ndirty_children == 0) {
                if (entry_ptr->clear_on_unprotect) {
                    HDassert(entry_ptr->is_dirty);

                    /* Set entry and flags for operation */
                    op_ptr   = entry_ptr;
                    op_flags = clear_flags;

                    /* Reset entry flag */
                    entry_ptr->clear_on_unprotect = FALSE;
                    entries_cleared++;
                    progress = TRUE;
                } /* end if */
                else if (entry_ptr->flush_immediately) {
                    HDassert(entry_ptr->is_dirty);

                    /* Set entry and flags for operation */
                    op_ptr   = entry_ptr;
                    op_flags = flush_flags;

                    /* Reset entry flag */
                    entry_ptr->flush_immediately = FALSE;
                    entries_flushed++;
                    progress = TRUE;
                } /* end else-if */
                else
                    /* No operation for this entry */
                    op_ptr = NULL;

                /* Check for operation */
                if (op_ptr) {
                    /* reset entries_removed_counter and
                     * last_entry_removed_ptr prior to the call to
                     * H5C__flush_single_entry() so that we can spot
                     * unexpected removals of entries from the cache,
                     * and set the restart_scan flag if proceeding
                     * would be likely to cause us to scan an entry
                     * that is no longer in the cache.
                     *
                     * Note that as of this writing,  this
                     * case cannot occur in the parallel case.
                     *
                     * Note also that there is no test code to verify
                     * that this code actually works (although similar code
                     * in the serial version exists and is tested).
                     */
                    cache_ptr->entries_removed_counter = 0;
                    cache_ptr->last_entry_removed_ptr  = NULL;

                    /* Add this entry to the list of entries to collectively write
                     *
                     * This comment is misleading -- the entry will be added to the
                     * collective write list only if said list exists.
                     *
                     *                                    JRM -- 2/9/17
                     */
                    if (H5C__flush_single_entry(f, op_ptr, op_flags) < 0)
                        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "can't flush entry")

                    if (cache_ptr->entries_removed_counter != 0 || cache_ptr->last_entry_removed_ptr != NULL)
                        restart_scan = TRUE;
                } /* end if */
            }     /* end if */

            /* Remember "previous" pointer (after advancing entries) */
            prev_ptr = entry_ptr;

            /* Advance to next entry */
            entry_ptr = entry_ptr->next;

            /* Check for restarts, etc. */
            if ((entry_ptr != NULL) &&
                (restart_scan || (entry_ptr->is_dirty != next_is_dirty) || (entry_ptr->prev != prev_ptr) ||
                 entry_ptr->is_protected || !entry_ptr->is_pinned)) {
                /* Something has happened to the pinned entry list -- start
                 * over from the head.
                 *
                 * Recall that this code should be un-reachable at present,
                 * as all the operations by entries on flush that could cause
                 * it to be reachable are disallowed in the parallel case at
                 * present.  Hence the following assertion which should be
                 * removed if the above changes.
                 */

                HDassert(!restart_scan);
                HDassert(entry_ptr->is_dirty == next_is_dirty);
                HDassert(entry_ptr->prev == prev_ptr);
                HDassert(!entry_ptr->is_protected);
                HDassert(entry_ptr->is_pinned);

                HDassert(FALSE); /* see comment above */

                restart_scan = FALSE;

                entry_ptr = cache_ptr->pel_head_ptr;

                /* we don't keeps stats for pinned entry list scan
                 * restarts.  If this code ever becomes reachable,
                 * define the necessary field, and implement the
                 * the following macro:
                 *
                 * H5C__UPDATE_STATS_FOR_PEL_SCAN_RESTART(cache_ptr)
                 */
            } /* end if */
        }     /* end while ( ( entry_ptr != NULL ) &&
               *             ( ( entries_flushed > entries_to_flush ) ||
               *               ( entries_cleared > entries_to_clear ) ) )
               */
    }         /* end while ( ( ( entries_flushed > entries_to_flush ) ||
               *               ( entries_cleared > entries_to_clear ) ) &&
               *             ( progress ) )
               */

#if H5C_DO_SANITY_CHECKS
    HDassert(init_index_len == cache_ptr->index_len);
#endif /* H5C_DO_SANITY_CHECKS */

    if (entries_flushed != entries_to_flush || entries_cleared != entries_to_clear) {
        entry_ptr = cache_ptr->il_head;
        while (entry_ptr != NULL) {
            HDassert(!entry_ptr->clear_on_unprotect || (entry_ptr->ring > ring));
            HDassert(!entry_ptr->flush_immediately || (entry_ptr->ring > ring));
            entry_ptr = entry_ptr->il_next;
        } /* end while */

        HGOTO_ERROR(H5E_CACHE, H5E_CANTFLUSH, FAIL, "can't flush/clear all entries")
    } /* end if */

done:
    FUNC_LEAVE_NOAPI(ret_value)
} /* H5C__flush_candidates_in_ring() */
#endif /* H5_HAVE_PARALLEL */