1 /*-------------------------------------------------------------------------
2 *
3 * expandeddatum.c
4 * Support functions for "expanded" value representations.
5 *
6 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
7 * Portions Copyright (c) 1994, Regents of the University of California
8 *
9 *
10 * IDENTIFICATION
11 * src/backend/utils/adt/expandeddatum.c
12 *
13 *-------------------------------------------------------------------------
14 */
15 #include "postgres.h"
16
17 #include "utils/expandeddatum.h"
18 #include "utils/memutils.h"
19
20 /*
21 * DatumGetEOHP
22 *
23 * Given a Datum that is an expanded-object reference, extract the pointer.
24 *
25 * This is a bit tedious since the pointer may not be properly aligned;
26 * compare VARATT_EXTERNAL_GET_POINTER().
27 */
28 ExpandedObjectHeader *
DatumGetEOHP(Datum d)29 DatumGetEOHP(Datum d)
30 {
31 varattrib_1b_e *datum = (varattrib_1b_e *) DatumGetPointer(d);
32 varatt_expanded ptr;
33
34 Assert(VARATT_IS_EXTERNAL_EXPANDED(datum));
35 memcpy(&ptr, VARDATA_EXTERNAL(datum), sizeof(ptr));
36 Assert(VARATT_IS_EXPANDED_HEADER(ptr.eohptr));
37 return ptr.eohptr;
38 }
39
40 /*
41 * EOH_init_header
42 *
43 * Initialize the common header of an expanded object.
44 *
45 * The main thing this encapsulates is initializing the TOAST pointers.
46 */
47 void
EOH_init_header(ExpandedObjectHeader * eohptr,const ExpandedObjectMethods * methods,MemoryContext obj_context)48 EOH_init_header(ExpandedObjectHeader *eohptr,
49 const ExpandedObjectMethods *methods,
50 MemoryContext obj_context)
51 {
52 varatt_expanded ptr;
53
54 eohptr->vl_len_ = EOH_HEADER_MAGIC;
55 eohptr->eoh_methods = methods;
56 eohptr->eoh_context = obj_context;
57
58 ptr.eohptr = eohptr;
59
60 SET_VARTAG_EXTERNAL(eohptr->eoh_rw_ptr, VARTAG_EXPANDED_RW);
61 memcpy(VARDATA_EXTERNAL(eohptr->eoh_rw_ptr), &ptr, sizeof(ptr));
62
63 SET_VARTAG_EXTERNAL(eohptr->eoh_ro_ptr, VARTAG_EXPANDED_RO);
64 memcpy(VARDATA_EXTERNAL(eohptr->eoh_ro_ptr), &ptr, sizeof(ptr));
65 }
66
67 /*
68 * EOH_get_flat_size
69 * EOH_flatten_into
70 *
71 * Convenience functions for invoking the "methods" of an expanded object.
72 */
73
74 Size
EOH_get_flat_size(ExpandedObjectHeader * eohptr)75 EOH_get_flat_size(ExpandedObjectHeader *eohptr)
76 {
77 return eohptr->eoh_methods->get_flat_size(eohptr);
78 }
79
80 void
EOH_flatten_into(ExpandedObjectHeader * eohptr,void * result,Size allocated_size)81 EOH_flatten_into(ExpandedObjectHeader *eohptr,
82 void *result, Size allocated_size)
83 {
84 eohptr->eoh_methods->flatten_into(eohptr, result, allocated_size);
85 }
86
87 /*
88 * If the Datum represents a R/W expanded object, change it to R/O.
89 * Otherwise return the original Datum.
90 *
91 * Caller must ensure that the datum is a non-null varlena value. Typically
92 * this is invoked via MakeExpandedObjectReadOnly(), which checks that.
93 */
94 Datum
MakeExpandedObjectReadOnlyInternal(Datum d)95 MakeExpandedObjectReadOnlyInternal(Datum d)
96 {
97 ExpandedObjectHeader *eohptr;
98
99 /* Nothing to do if not a read-write expanded-object pointer */
100 if (!VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(d)))
101 return d;
102
103 /* Now safe to extract the object pointer */
104 eohptr = DatumGetEOHP(d);
105
106 /* Return the built-in read-only pointer instead of given pointer */
107 return EOHPGetRODatum(eohptr);
108 }
109
110 /*
111 * Transfer ownership of an expanded object to a new parent memory context.
112 * The object must be referenced by a R/W pointer, and what we return is
113 * always its "standard" R/W pointer, which is certain to have the same
114 * lifespan as the object itself. (The passed-in pointer might not, and
115 * in any case wouldn't provide a unique identifier if it's not that one.)
116 */
117 Datum
TransferExpandedObject(Datum d,MemoryContext new_parent)118 TransferExpandedObject(Datum d, MemoryContext new_parent)
119 {
120 ExpandedObjectHeader *eohptr = DatumGetEOHP(d);
121
122 /* Assert caller gave a R/W pointer */
123 Assert(VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(d)));
124
125 /* Transfer ownership */
126 MemoryContextSetParent(eohptr->eoh_context, new_parent);
127
128 /* Return the object's standard read-write pointer */
129 return EOHPGetRWDatum(eohptr);
130 }
131
132 /*
133 * Delete an expanded object (must be referenced by a R/W pointer).
134 */
135 void
DeleteExpandedObject(Datum d)136 DeleteExpandedObject(Datum d)
137 {
138 ExpandedObjectHeader *eohptr = DatumGetEOHP(d);
139
140 /* Assert caller gave a R/W pointer */
141 Assert(VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(d)));
142
143 /* Kill it */
144 MemoryContextDelete(eohptr->eoh_context);
145 }
146