summaryrefslogtreecommitdiffstats
path: root/src/H5I.c
blob: 75bb5c9dd3f0a45b5f46bd4c80603480c913b8b8 (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
/****************************************************************************
 * NCSA HDF								    *
 * Software Development Group						    *
 * National Center for Supercomputing Applications			    *
 * University of Illinois at Urbana-Champaign				    *
 * 605 E. Springfield, Champaign IL 61820				    *
 *									    *
 * For conditions of distribution and use, see the accompanying		    *
 * hdf/COPYING file.							    *
 *									    *
 ****************************************************************************/

#ifdef RCSID
static char		RcsId[] = "@(#)$Revision$";
#endif

/* $Id$ */

/*
 * FILE:	H5I.c - Internal storage routines for handling "IDs"
 *     
 * REMARKS:	ID's which allow objects (void *'s currently) to be bundled
 *		into "groups" for more general storage.
 * 
 * DESIGN:	The groups are stored in an array of pointers to store each
 *		group in an element. Each "group" node contains a link to a
 *		hash table to manage the IDs in each group.  The allowed
 *		"groups" are stored in an enum (called group_t) in
 *		H5Ipublic.h.
 *		
 * AUTHOR:	Quincey Koziol
 *
 * MODIFICATIONS:
 *	1/3/96	- Starting writing specs & coding prototype
 *	1/7/96	- Finished coding prototype
 *	6/10/97 - Moved into HDF5 library
 */
#include <H5private.h>
#include <H5Iprivate.h>
#include <H5Eprivate.h>
#include <H5MMprivate.h>

/* Interface initialialization? */
#define PABLO_MASK	H5I_mask
static intn interface_initialize_g = 0;
#define INTERFACE_INIT H5I_init_interface
static herr_t H5I_init_interface(void);

/*
 * Define the following macro for fast hash calculations (but limited
 * hash sizes)
 */
#define HASH_SIZE_POWER_2

/* Define the following macro for atom caching over all the atoms */
#define IDS_ARE_CACHED

/*-------------------- Locally scoped variables -----------------------------*/

#ifdef IDS_ARE_CACHED
#  define ID_CACHE_SIZE 4	      /*# of previous atoms cached	   */
#endif

/*
 * Number of bits to use for Group ID in each atom. Increase if H5I_NGROUPS
 * becomes too large (an assertion would fail in H5I_init_interface). This is
 * the only number that must be changed since all other bit field sizes and
 * masks are calculated from GROUP_BITS.
 */
#define GROUP_BITS	5
#define GROUP_MASK	((1<<GROUP_BITS)-1)

/*
 * Number of bits to use for the Atom index in each atom (assumes 8-bit
 * bytes). We don't use the sign bit.
 */
#define ID_BITS		((sizeof(hid_t)*8)-(GROUP_BITS+1))
#define ID_MASK		((1<<ID_BITS)-1)

/* Map an atom to a Group number */
#define H5I_GROUP(a)	((H5I_type_t)(((hid_t)(a)>>ID_BITS) & GROUP_MASK))


#ifdef HASH_SIZE_POWER_2
/*
 * Map an ID to a hash location (assumes s is a power of 2 and smaller
 * than the ID_MASK constant).
 */
#  define H5I_LOC(a,s)	((hid_t)((size_t)(a)&((s)-1)))
#else
/*
 * Map an ID to a hash location.
 */
#  define H5I_LOC(a,s)	(((hid_t)(a)&ID_MASK)%(s))
#endif

/* Combine a Group number and an atom index into an atom */
#define H5I_MAKE(g,i)	((((hid_t)(g)&GROUP_MASK)<<ID_BITS)|	  \
			     ((hid_t)(i)&ID_MASK))

#ifdef IDS_ARE_CACHED
/* Array of pointers to ID groups */
static hid_t H5I_id_cache_g[ID_CACHE_SIZE] = {-1, -1, -1, -1};
static void *H5I_obj_cache_g[ID_CACHE_SIZE];
#endif

/* Array of pointers to atomic groups */
static H5I_id_group_t *H5I_id_group_list_g[H5I_NGROUPS];

/* Pointer to the atom node free list */
static H5I_id_info_t *H5I_id_free_list_g = NULL;

/*--------------------- Local function prototypes ---------------------------*/
static H5I_id_info_t *H5I_find_id(hid_t id);
static H5I_id_info_t *H5I_get_id_node(void);
static herr_t H5I_release_id_node(H5I_id_info_t *id);
static herr_t H5I_debug(H5I_type_t grp);


/*-------------------------------------------------------------------------
 * Function:	H5I_init_interface
 *
 * Purpose:	Initialize interface-specific information.
 *
 * Return:	Success:	Non-negative
 *
 *		Failure:	Negative
 *
 * Programmer:	
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static herr_t 
H5I_init_interface(void)
{
    herr_t		    ret_value = SUCCEED;
    FUNC_ENTER(H5I_init_interface, FAIL);

    /*
     * Make certain the ID types don't overflow the number of bits allocated
     * for them in an ID.
     */
    assert(H5I_NGROUPS<=(1<<GROUP_BITS));

    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5I_term_interface
 *
 * Purpose:	Terminate the H5I interface: release all memory, reset all
 *		global variables to initial values. This only happens if all
 *		groups have been destroyed from other interfaces.
 *
 * Return:	Success:	Positive if any action was taken that might
 *				affect some other interface; zero otherwise.
 *
 * 		Failure:	Negative.
 *
 * Programmer:	
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
intn
H5I_term_interface(void)
{
    H5I_id_group_t	*grp_ptr;
    H5I_id_info_t	*curr;
    H5I_type_t		grp;
    intn		n=0;

    if (interface_initialize_g) {

	/* How many groups are still being used? */
	for (grp=(H5I_type_t)0; grp<H5I_NGROUPS; grp++) {
	    if ((grp_ptr=H5I_id_group_list_g[grp]) && grp_ptr->id_list) {
		n++;
	    }
	}

	/* If no groups are used then clean  up */
	if (0==n) {
	    for (grp=(H5I_type_t)0; grp<H5I_NGROUPS; grp++) {
		grp_ptr = H5I_id_group_list_g[grp];
		H5MM_xfree(grp_ptr);
		H5I_id_group_list_g[grp] = NULL;
	    }

	    /* Release the global free list */
	    while (H5I_id_free_list_g) {
		curr = H5I_id_free_list_g;
		H5I_id_free_list_g = H5I_id_free_list_g->next;
		H5MM_xfree(curr);
	    }
	}

	/* Mark interface closed */
	interface_initialize_g = 0;
    }
    return n;
}


/*-------------------------------------------------------------------------
 * Function:	H5I_init_group
 *
 * Purpose:	Initialize an ID group whose ID number is specified by GRP,
 *		If the group has already been initialized, this routine just
 *		increments the count of number of initializations and returns
 *		without trying to change the size of the hash table.  A
 *		specific number (RESERVED) of group entries may be reserved
 *		to enable "constant" values to be handed out which are valid
 *		IDs in the group, but which do not map to any data structures
 *		and are not allocated dynamicly later. HASH_SIZE is the
 *		minimum hash table size to use for the group. FREE_FUNC is
 *		called with an object pointer when the object is removed from
 *		the group.
 *
 * Return:	Success:	Non-negative
 *
 *		Failure:	Negative
 *
 * Programmer:	Robb Matzke
 *		Friday, February 19, 1999
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
intn 
H5I_init_group(H5I_type_t grp, size_t hash_size, uintn reserved,
	       H5I_free_t free_func)
{
    H5I_id_group_t	*grp_ptr = NULL;	/*ptr to the atomic group*/
    intn		ret_value = SUCCEED;	/*return value		*/

    FUNC_ENTER(H5I_init_group, FAIL);

    /* Check arguments */
    if ((grp <= H5I_BADID || grp >= H5I_NGROUPS) && hash_size > 0) {
	HGOTO_DONE(FAIL);
    }
#ifdef HASH_SIZE_POWER_2
    /*
     * If anyone knows a faster test for a power of two, please change this
     * silly code -QAK
     */
    if (!(hash_size == 2 || hash_size == 4 || hash_size == 8 ||
	  hash_size == 16 || hash_size == 32 || hash_size == 64 ||
	  hash_size == 128 || hash_size == 256 || hash_size == 512 ||
	  hash_size == 1024 || hash_size == 2048 || hash_size == 4096 ||
	  hash_size == 8192 || hash_size == 16374 || hash_size == 32768 ||
	  hash_size == 65536 || hash_size == 131072 || hash_size == 262144 ||
	  hash_size == 524288 || hash_size == 1048576 ||
	  hash_size == 2097152 || hash_size == 4194304 ||
	  hash_size == 8388608 || hash_size == 16777216 ||
	  hash_size == 33554432 || hash_size == 67108864 ||
	  hash_size == 134217728 || hash_size == 268435456))
	HGOTO_DONE(FAIL);
#endif /* HASH_SIZE_POWER_2 */

    if (H5I_id_group_list_g[grp] == NULL) {
	/* Allocate the group information for new group */
	if (NULL==(grp_ptr = H5MM_calloc(sizeof(H5I_id_group_t)))) {
	    HGOTO_ERROR (H5E_RESOURCE, H5E_NOSPACE, FAIL,
			 "memory allocation failed");
	}
	H5I_id_group_list_g[grp] = grp_ptr;
    } else {
	/* Get the pointer to the existing group */
	grp_ptr = H5I_id_group_list_g[grp];
    }

    if (grp_ptr->count == 0) {
	/* Initialize the ID group structure for new groups */
	grp_ptr->hash_size = hash_size;
	grp_ptr->reserved = reserved;
	grp_ptr->wrapped = 0;
	grp_ptr->ids = 0;
	grp_ptr->nextid = reserved;
	grp_ptr->free_func = free_func;
	grp_ptr->id_list = H5MM_calloc(hash_size*sizeof(H5I_id_info_t *));
	if (NULL==grp_ptr->id_list) {
	    HGOTO_ERROR (H5E_RESOURCE, H5E_NOSPACE, FAIL,
			 "memory allocation failed");
	}
    }
    
    /* Increment the count of the times this group has been initialized */
    grp_ptr->count++;

  done:
    if (ret_value<0) {
	/* Error condition cleanup */
	if (grp_ptr != NULL) {
	    H5MM_xfree(grp_ptr->id_list);
	    H5MM_xfree(grp_ptr);
	}
    }

    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5I_nmembers
 *
 * Purpose:	Returns the number of members in a group.
 *
 * Return:	Success:	Number of members; zero if the group is empty
 *				or has been deleted.
 *
 *		Failure:	Negative
 *
 * Programmer:	Robb Matzke
 *              Wednesday, March 24, 1999
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
intn
H5I_nmembers(H5I_type_t grp)
{
    H5I_id_group_t	*grp_ptr = NULL;
    H5I_id_info_t	*cur=NULL;
    intn		n=0;
    uintn		i;

    FUNC_ENTER(H5I_nmembers, FAIL);

    if (grp<=H5I_BADID || grp>=H5I_NGROUPS) {
	HRETURN_ERROR(H5E_ARGS, H5E_BADRANGE, FAIL, "invalid group number");
    }
    if (NULL==(grp_ptr=H5I_id_group_list_g[grp]) || grp_ptr->count<=0) {
	HRETURN(0);
    }

    for (i=0; i<grp_ptr->hash_size; i++) {
	for (cur=grp_ptr->id_list[i]; cur; cur=cur->next) {
	    n++;
	}
    }
    FUNC_LEAVE(n);
}


/*-------------------------------------------------------------------------
 * Function:	H5I_clear_group
 *
 * Purpose:	Removes all objects from the group, calling the free
 *		function for each object regardless of the reference count.
 *
 * Return:	Success:	Non-negative
 *
 *		Failure:	negative
 *
 * Programmer:	Robb Matzke
 *              Wednesday, March 24, 1999
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5I_clear_group(H5I_type_t grp)
{
    H5I_id_group_t	*grp_ptr = NULL;	/* ptr to the atomic group */
    H5I_id_info_t	*cur=NULL, *next=NULL;
    intn		ret_value = SUCCEED;
    uintn		i;

    FUNC_ENTER(H5I_clear_group, FAIL);

    if (grp <= H5I_BADID || grp >= H5I_NGROUPS) {
	HGOTO_DONE(FAIL);
    }
    
    grp_ptr = H5I_id_group_list_g[grp];
    if (grp_ptr == NULL || grp_ptr->count <= 0) {
	HGOTO_DONE(FAIL);
    }

#ifdef IDS_ARE_CACHED
    /*
     * Remove atoms from the global atom cache.
     */
    for (i=0; i<ID_CACHE_SIZE; i++) {
	if (H5I_GROUP(H5I_id_cache_g[i]) == grp) {
	    H5I_id_cache_g[i] = (-1);
	    H5I_obj_cache_g[i] = NULL;
	}
    }
#endif /* IDS_ARE_CACHED */

    /*
     * Call free method for all objects in group regardless of their reference
     * counts. Ignore the return value from from the free method and remove
     * object from group regardless.
     */
    if (grp_ptr->free_func) {
	for (i=0; i<grp_ptr->hash_size; i++) {
	    for (cur=grp_ptr->id_list[i]; cur; cur=next) {
		/* Free the object regardless of reference count */
		if ((grp_ptr->free_func)(cur->obj_ptr)<0) {
#if H5I_DEBUG
		    if (H5DEBUG(I)) {
			fprintf(H5DEBUG(I), "H5I: free grp=%d obj=0x%08lx "
				"failure ignored\n", (int)grp,
				(unsigned long)(cur->obj_ptr));
		    }
#endif /*H5I_DEBUG*/
		}
		    
		/* Add ID struct to free list */
		next = cur->next;
		H5I_release_id_node(cur);
	    }
	    grp_ptr->id_list[i]=NULL;
	}
    }
    
  done:
    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5I_destroy_group
 *
 * Purpose:	Decrements the reference count on an entire group of IDs.
 *		If the group reference count becomes zero then the group is
 *		destroyed along with all atoms in that group regardless of
 *		their reference counts.	 Destroying IDs involves calling
 *		the free-func for each ID's object and then adding the ID
 *		struct to the ID free list.
 *		
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	Unknown
 *
 * Modifications:
 *
 *	Robb Matzke, 25 Feb 1998
 *	IDs are freed when a group is destroyed.
 *
 *-------------------------------------------------------------------------
 */
herr_t
H5I_destroy_group(H5I_type_t grp)
{
    H5I_id_group_t	*grp_ptr = NULL;	/* ptr to the atomic group */
    intn		ret_value = SUCCEED;

    FUNC_ENTER(H5I_destroy_group, FAIL);

    if (grp <= H5I_BADID || grp >= H5I_NGROUPS) {
	HGOTO_DONE(FAIL);
    }
    
    grp_ptr = H5I_id_group_list_g[grp];
    if (grp_ptr == NULL || grp_ptr->count <= 0) {
	HGOTO_DONE(FAIL);
    }

    /*
     * Decrement the number of users of the atomic group.  If this is the
     * last user of the group then release all atoms from the group.  The
     * free function is invoked for each atom being freed.
     */
    if (1==grp_ptr->count) {
	H5I_clear_group(grp);
	H5MM_xfree(grp_ptr->id_list);
	HDmemset (grp_ptr, 0, sizeof(*grp_ptr));
    } else {
	--(grp_ptr->count);
    }
    
  done:
    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5I_register
 *
 * Purpose:	Registers an OBJECT in a GROUP and returns an ID for it.
 *		This routine does _not_ check for unique-ness of the objects,
 *		if you register an object twice, you will get two different
 *		IDs for it.  This routine does make certain that each ID in a
 *		group is unique.  IDs are created by getting a unique number
 *		for the group the ID is in and incorporating the group into
 *		the ID which is returned to the user.
 *
 * Return:	Success:	New object id.
 *
 *		Failure:	Negative
 *
 * Programmer:	Unknown
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
hid_t 
H5I_register(H5I_type_t grp, void *object)
{
    H5I_id_group_t	*grp_ptr=NULL;	/*ptr to the group		*/
    H5I_id_info_t	*id_ptr=NULL;	/*ptr to the new ID information */
    hid_t		new_id;		/*new ID			*/
    uintn		hash_loc;	/*new item's hash table location*/
    hid_t		next_id;	/*next ID to check		*/
    hid_t		ret_value=SUCCEED; /*return value		*/
    H5I_id_info_t	*curr_id;	/*ptr to the current atom	*/
    uintn		i;		/*counter			*/
    
    FUNC_ENTER(H5I_register, FAIL);

    /* Check arguments */
    if (grp <= H5I_BADID || grp >= H5I_NGROUPS) {
	HGOTO_DONE(FAIL);
    }
    grp_ptr = H5I_id_group_list_g[grp];
    if (grp_ptr == NULL || grp_ptr->count <= 0) {
	HGOTO_DONE(FAIL);
    }
    if ((id_ptr = H5I_get_id_node()) == NULL) {
	HGOTO_DONE(FAIL);
    }

    /* Create the struct & it's ID */
    new_id = H5I_MAKE(grp, grp_ptr->nextid);
    id_ptr->id = new_id;
    id_ptr->count = 1; /*initial reference count*/
    id_ptr->obj_ptr = object;
    id_ptr->next = NULL;

    /* hash bucket already full, prepend to front of chain */
    hash_loc = grp_ptr->nextid % (uintn) grp_ptr->hash_size;
    if (grp_ptr->id_list[hash_loc] != NULL) {
	id_ptr->next = grp_ptr->id_list[hash_loc];
    }

    /* Insert into the group */
    grp_ptr->id_list[hash_loc] = id_ptr;
    grp_ptr->ids++;
    grp_ptr->nextid++;

    /*
     * This next section of code checks for the 'nextid' getting too large and
     * wrapping around, thus necessitating checking for duplicate IDs being
     * handed out.
     */
    if (grp_ptr->nextid > (uintn)ID_MASK) {
	grp_ptr->wrapped = 1;
	grp_ptr->nextid = grp_ptr->reserved;
    }

    /*
     * If we've wrapped around then we need to check for duplicate id's being
     * handed out.
     */
    if (grp_ptr->wrapped) {
	/*
	 * Make sure we check all available ID's.  If we're about at the end
	 * of the range then wrap around and check the beginning values.  If
	 * we check all possible values and didn't find any free ones *then*
	 * we can fail.
	 */
	for (i=grp_ptr->reserved; i<ID_MASK; i++) {
	    /* Handle end of range by wrapping to beginning */
	    if (grp_ptr->nextid>(uintn)ID_MASK) {
		grp_ptr->nextid = grp_ptr->reserved;
	    }

	    /* new ID to check for */
	    next_id = H5I_MAKE(grp, grp_ptr->nextid);
	    hash_loc = H5I_LOC (grp_ptr->nextid, grp_ptr->hash_size);
	    curr_id = grp_ptr->id_list[hash_loc];
	    if (curr_id == NULL) break; /* Ha! this is not likely... */

	    while (curr_id) {
		if (curr_id->id == next_id) break;
		curr_id = curr_id->next;
	    }
	    if (!curr_id) break; /* must not have found a match */
	    grp_ptr->nextid++;
	}

	if (i>=(uintn)ID_MASK) {
	    /* All the IDs are gone! */
	    HGOTO_DONE(FAIL);
	}
    }
    ret_value = new_id;

  done:
    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5I_object
 *
 * Purpose:	Find an object pointer for the specified ID.
 *
 * Return:	Success:	Non-null object pointer associated with the
 *				specified ID.
 *
 *		Failure:	NULL
 *
 * Programmer:	
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
void * 
H5I_object(hid_t id)
{
    H5I_id_info_t	*id_ptr = NULL;		/*ptr to the new atom	*/
    void		*ret_value = NULL;	/*return value		*/
#ifdef IDS_ARE_CACHED
    uintn		i;			/*local counter		*/
#endif /* IDS_ARE_CACHED */

    FUNC_ENTER(H5I_object, NULL);

#ifdef IDS_ARE_CACHED
    /*
     * Look for the ID in the cache first. Implement a simple "move
     * forward" caching scheme by swapping the found cache item with the
     * previous cache item.  This gradually migrates used cache items toward
     * the front of the cache and unused items toward the end.	For instance,
     * finding `e' in the cache results in:
     *
     * Before: a b c d e f g h i j
     *	       | | |  X	 | | | | |
     * After:  a b c e d f g h i j
     */
    for (i=0; i<ID_CACHE_SIZE; i++)
	if (H5I_id_cache_g[i] == id) {
	    ret_value = H5I_obj_cache_g[i];
	    if (i > 0) {
		hid_t t_id = H5I_id_cache_g[i-1];
		void *t_obj = H5I_obj_cache_g[i-1];
		H5I_id_cache_g[i-1] = H5I_id_cache_g[i];
		H5I_obj_cache_g[i-1] = H5I_obj_cache_g[i];
		H5I_id_cache_g[i] = t_id;
		H5I_obj_cache_g[i] = t_obj;
	    }
	    HGOTO_DONE(ret_value);
	}
#endif /* IDS_ARE_CACHED */

    /* General lookup of the ID */
    if (NULL==(id_ptr = H5I_find_id(id))) HGOTO_DONE(NULL);

    /* Check if we've found the correct ID */
    if (id_ptr) ret_value = id_ptr->obj_ptr;

  done:
    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5I_get_type
 *
 * Purpose:	Given an object ID return the group (type) to which it
 *		belongs.  The ID need not be the ID of an object which
 *		currently exists because the group number (type) is encoded
 *		in the object ID.
 *
 * Return:	Success:	A valid group number (type)
 *
 *		Failure:	H5I_BADID, a negative value.
 *
 * Programmer:	Robb Matzke
 *		Friday, February 19, 1999
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
H5I_type_t 
H5I_get_type(hid_t id)
{
    H5I_type_t		ret_value = H5I_BADID;

    FUNC_ENTER(H5I_get_type, H5I_BADID);

    if (id>0) ret_value = H5I_GROUP(id);
    assert(ret_value>=H5I_BADID && ret_value<H5I_NGROUPS);

    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5Iget_type
 *
 * Purpose:	The public version of H5I_get_type(), obtains a group number
 *		(type) when given an ID.  The ID need not be the ID of an
 *		object which currently exists because the group number is
 *		encoded as part of the ID.
 *
 * Return:	Success:	Group number (type)
 *
 *		Failure:	H5I_BADID, a negative value
 *
 * Programmer:	
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
H5I_type_t
H5Iget_type(hid_t id)
{
    H5I_type_t		ret_value = H5I_BADID;

    FUNC_ENTER(H5Iget_type, H5I_BADID);
    H5TRACE1("It","i",id);

    if (ret_value <= H5I_BADID || ret_value >= H5I_NGROUPS) {
	HGOTO_DONE(H5I_BADID);
    }
    ret_value = H5I_get_type(id);

done:
    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5I_remove
 *
 * Purpose:	Removes the specified ID from its group.
 *
 * Return:	Success:	A pointer to the object that was removed, the
 *				same pointer which would have been found by
 *				calling H5I_object().
 *
 *		Failure:	NULL
 *
 * Programmer:	
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
void * 
H5I_remove(hid_t id)
{
    H5I_id_group_t	*grp_ptr = NULL;/*ptr to the atomic group	*/
    H5I_id_info_t	*curr_id;	/*ptr to the current atom	*/
    H5I_id_info_t	*last_id;	/*ptr to the last atom		*/
    H5I_type_t		grp;		/*atom's atomic group		*/
    uintn		hash_loc;	/*atom's hash table location	*/
#ifdef IDS_ARE_CACHED
    uintn		i;		/*local counting variable	*/
#endif
    void *	      ret_value = NULL;	/*return value			*/

    FUNC_ENTER(H5I_remove, NULL);

    /* Check arguments */
    grp = H5I_GROUP(id);
    if (grp <= H5I_BADID || grp >= H5I_NGROUPS) HGOTO_DONE(NULL);
    grp_ptr = H5I_id_group_list_g[grp];
    if (grp_ptr == NULL || grp_ptr->count <= 0) HGOTO_DONE(NULL);

    /* Get the bucket in which the ID is located */
    hash_loc = (uintn) H5I_LOC(id, grp_ptr->hash_size);
    curr_id = grp_ptr->id_list[hash_loc];
    if (curr_id == NULL) HGOTO_DONE(NULL);

    last_id = NULL;
    while (curr_id != NULL) {
	if (curr_id->id == id) break;
	last_id = curr_id;
	curr_id = curr_id->next;
    }

    if (curr_id != NULL) {
	if (last_id == NULL) {
	    /* ID is the first in the chain */
	    grp_ptr->id_list[hash_loc] = curr_id->next;
	} else {
	    last_id->next = curr_id->next;
	}
	ret_value = curr_id->obj_ptr;
	H5I_release_id_node(curr_id);
    } else {
	/* couldn't find the ID in the proper place */
	HGOTO_DONE(NULL);
    }

#ifdef IDS_ARE_CACHED
    /* Delete object from cache */
    for (i = 0; i < ID_CACHE_SIZE; i++)
	if (H5I_id_cache_g[i] == id) {
	    H5I_id_cache_g[i] = (-1);
	    H5I_obj_cache_g[i] = NULL;
	    break; /* we assume there is only one instance in the cache */
	}
#endif /* IDS_ARE_CACHED */

    /* Decrement the number of IDs in the group */
    (grp_ptr->ids)--;

  done:
    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5I_dec_ref
 *
 * Purpose:	Decrements the number of references outstanding for an ID.
 *		This will fail if the group is not a reference counted group.
 *		The ID group's 'free' function will be called for the ID
 *		if the reference count for the ID reaches 0 and a free
 *		function has been defined at group creation time.
 *
 * Return:	Success:	New reference count.
 *
 *		Failure:	Negative
 *
 * Programmer:	Unknown
 *
 * Modifications:
 *
 *	Robb Matzke, 19 Feb 1998
 *	It is no longer an error when the reference count of an item reaches
 *	zero and no `free' function has been defined.  The object is still
 *	removed from the list.
 *
 *	Robb Matzke, 30 Dec 1998
 *	Fixed a bug where the return value was always zero instead of the new
 *	reference count.
 *
 *	Robb Matzke, 19 Feb 1999
 *	If the free method is defined and fails then the object is not
 *	removed from the group and its reference count is not decremented.
 *	The group number is now passed to the free method.
 *
 *-------------------------------------------------------------------------
 */
intn
H5I_dec_ref(hid_t id)
{
    H5I_type_t		grp = H5I_GROUP(id);	/*group the object is in*/
    H5I_id_group_t	*grp_ptr = NULL;	/*ptr to the group	*/
    H5I_id_info_t	*id_ptr = NULL;		/*ptr to the new ID	*/
    intn		ret_value = FAIL;	/*return value		*/

    FUNC_ENTER(H5I_dec_ref, FAIL);

    /* Check arguments */
    grp_ptr = H5I_id_group_list_g[grp];
    if (grp_ptr == NULL || grp_ptr->count <= 0) {
	HRETURN(FAIL);
    }
    
    /* General lookup of the ID */
    if ((id_ptr=H5I_find_id(id))) {
	/*
	 * If this is the last reference to the object then invoke the group's
	 * free method on the object. If the free method is undefined or
	 * successful then remove the object from the group; otherwise leave
	 * the object in the group without decrementing the reference
	 * count. If the reference count is more than one then decrement the
	 * reference count without calling the free method.
	 *
	 * Beware: the free method may call other H5I functions.
	 */
	if (1==id_ptr->count) {
	    if (!grp_ptr->free_func ||
		(grp_ptr->free_func)(id_ptr->obj_ptr)>=0) {
		H5I_remove(id);
		ret_value = 0;
	    } else {
		ret_value = 1;
	    }
	} else {
	    ret_value = --(id_ptr->count);
	}
    }
    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5I_search
 *
 * Purpose:	Apply function FUNC to each member of group GRP and return a
 *		pointer to the first object for which FUNC returns non-zero.
 *		The FUNC should take a pointer to the object and the KEY as
 *		arguments and return non-zero to terminate the search (zero
 *		to continue).
 *
 * Limitation:	Currently there is no way to start searching from where a
 *		previous search left off.
 *
 * Return:	Success:	The first object in the group for which FUNC
 *				returns non-zero. NULL if FUNC returned zero
 *				for every object in the group.
 *
 *		Failure:	NULL
 *
 * Programmer:	Robb Matzke
 *		Friday, February 19, 1999
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
void *
H5I_search(H5I_type_t grp, H5I_search_func_t func, const void *key)
{
    H5I_id_group_t	*grp_ptr = NULL;	/*ptr to the group	*/
    H5I_id_info_t	*id_ptr = NULL;		/*ptr to the new ID	*/
    uintn		i;			/*counter		*/
    void		*ret_value = NULL;	/*return value		*/

    FUNC_ENTER(H5I_search, NULL);

    /* Check arguments */
    if (grp <= H5I_BADID || grp >= H5I_NGROUPS) {
	HGOTO_DONE(NULL);
    }
    grp_ptr = H5I_id_group_list_g[grp];
    if (grp_ptr == NULL || grp_ptr->count <= 0) {
	HGOTO_DONE(NULL);
    }

    /* Start at the beginning of the array */
    for (i=0; i<grp_ptr->hash_size; i++) {
	id_ptr = grp_ptr->id_list[i];
	while (id_ptr) {
	    if ((*func)(id_ptr->obj_ptr, key)) {
		HGOTO_DONE(id_ptr->obj_ptr);	/*found the item*/
	    }
	    id_ptr = id_ptr->next;
	}
    }

  done:
    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5I_find_id
 *
 * Purpose:	Given an object ID find the info struct that describes the
 *		object.
 *
 * Return:	Success:	Ptr to the object's info struct.
 *
 *		Failure:	NULL
 *
 * Programmer:	
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static H5I_id_info_t *
H5I_find_id(hid_t id)
{
    H5I_id_group_t	*grp_ptr = NULL;	/*ptr to the group	*/
    H5I_id_info_t	*id_ptr = NULL;		/*ptr to the new ID	*/
    H5I_type_t		grp;			/*ID's group		*/
    uintn		hash_loc;		/*bucket pointer	*/
    H5I_id_info_t	*ret_value = NULL;	/*return value		*/

    FUNC_ENTER(H5I_find_id, NULL);

    /* Check arguments */
    grp = H5I_GROUP(id);
    if (grp <= H5I_BADID || grp >= H5I_NGROUPS) {
	HGOTO_DONE(NULL);
    }
    grp_ptr = H5I_id_group_list_g[grp];
    if (grp_ptr == NULL || grp_ptr->count <= 0) {
	HGOTO_DONE(NULL);
    }

    /* Get the bucket in which the ID is located */
    hash_loc = (uintn)H5I_LOC(id, grp_ptr->hash_size);
    id_ptr = grp_ptr->id_list[hash_loc];
    if (id_ptr == NULL) {
	HGOTO_DONE(NULL);
    }

    /* Scan the bucket's linked list for a match */
    while (id_ptr) {
	if (id_ptr->id == id) break;
	id_ptr = id_ptr->next;
    }
    ret_value = id_ptr;

#ifdef IDS_ARE_CACHED
    /* Add id to the end of the cache */
    H5I_id_cache_g[ID_CACHE_SIZE-1] = id;
    H5I_obj_cache_g[ID_CACHE_SIZE-1] = id_ptr->obj_ptr;
#endif /* IDS_ARE_CACHED */

  done:
    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5I_get_id_node
 *
 * Purpose:	Either gets an ID node from the free list (if there is one
 *		available) or allocate a node.
 *
 * Return:	Success:	ID pointer
 *
 *		Failure:	NULL
 *
 * Programmer:	
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static H5I_id_info_t *
H5I_get_id_node(void)
{
    H5I_id_info_t	*ret_value = NULL;

    FUNC_ENTER(H5I_get_id_node, NULL);

    if (H5I_id_free_list_g != NULL) {
	ret_value = H5I_id_free_list_g;
	H5I_id_free_list_g = H5I_id_free_list_g->next;
    } else if (NULL==(ret_value = H5MM_malloc(sizeof(H5I_id_info_t)))) {
	HRETURN_ERROR (H5E_RESOURCE, H5E_NOSPACE, NULL,
		       "memory allocation failed");
    }

    FUNC_LEAVE(ret_value);
}


/*-------------------------------------------------------------------------
 * Function:	H5I_release_id_node
 *
 * Purpose:	Release an ID node and return it to the free list.
 *
 * Return:	Success:	Non-negative
 *
 *		Failure:	Negative
 *
 * Programmer:	
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5I_release_id_node(H5I_id_info_t *id)
{
    FUNC_ENTER(H5I_release_id_node, FAIL);

    /* Insert the ID at the beginning of the free list */
    id->next = H5I_id_free_list_g;
    H5I_id_free_list_g = id;

    FUNC_LEAVE(SUCCEED);
}


/*-------------------------------------------------------------------------
 * Function:	H5I_debug
 *
 * Purpose:	Dump the contents of a group to stderr for debugging.
 *
 * Return:	Success:	Non-negative
 *
 * 		Failure:	Negative
 *
 * Programmer:	Robb Matzke
 *		Friday, February 19, 1999
 *
 * Modifications:
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5I_debug(H5I_type_t grp)
{
    H5I_id_group_t	*grp_ptr;
    H5I_id_info_t	*cur;
    int			is, js;
    unsigned int	iu;

    FUNC_ENTER(H5I_debug, FAIL);
    
    fprintf(stderr, "Dumping group %d\n", (int)grp);
    grp_ptr = H5I_id_group_list_g[grp];

    /* Header */
    fprintf(stderr, "	 count	   = %u\n", grp_ptr->count);
    fprintf(stderr, "	 reserved  = %u\n", grp_ptr->reserved);
    fprintf(stderr, "	 wrapped   = %u\n", grp_ptr->wrapped);
    fprintf(stderr, "	 hash_size = %lu\n",
	    (unsigned long)grp_ptr->hash_size);
    fprintf(stderr, "	 ids	   = %u\n", grp_ptr->ids);
    fprintf(stderr, "	 nextid	   = %u\n", grp_ptr->nextid);

    /* Cache */
    fprintf(stderr, "	 Cache:\n");
    for (is=0; is<ID_CACHE_SIZE; is++) {
	if (H5I_GROUP(H5I_id_cache_g[is])==grp) {
	    fprintf(stderr, "	     Entry-%d, ID=%lu\n",
		    is, (unsigned long)(H5I_id_cache_g[is]));
	}
    }

    /* List */
    fprintf(stderr, "	 List:\n");
    for (iu=0; iu<grp_ptr->hash_size; iu++) {
	for (js=0, cur=grp_ptr->id_list[iu]; cur; cur=cur->next, js++) {
	    fprintf(stderr, "	     #%u.%d\n", iu, js);
	    fprintf(stderr, "		 id = %lu\n",
		    (unsigned long)(cur->id));
	    fprintf(stderr, "		 count = %u\n", cur->count);
	    fprintf(stderr, "		 obj   = 0x%08lx\n",
		    (unsigned long)(cur->obj_ptr));
	}
    }

    FUNC_LEAVE(SUCCEED);
}