PostgreSQL Source Code: src/backend/utils/adt/expandeddatum.c Source File

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expandeddatum.c
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1/*-------------------------------------------------------------------------
2 *
3 * expandeddatum.c
4 * Support functions for "expanded" value representations.
5 *
6 * Portions Copyright (c) 1996-2025, 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 */
28ExpandedObjectHeader *
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 */
47void
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
74Size
75 EOH_get_flat_size(ExpandedObjectHeader *eohptr)
76{
77 return eohptr->eoh_methods->get_flat_size(eohptr);
78}
79
80void
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 */
94Datum
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 */
117Datum
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 */
135void
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}
size_t Size
Definition: c.h:610
ExpandedObjectHeader * DatumGetEOHP(Datum d)
Definition: expandeddatum.c:29
void EOH_flatten_into(ExpandedObjectHeader *eohptr, void *result, Size allocated_size)
Definition: expandeddatum.c:81
void EOH_init_header(ExpandedObjectHeader *eohptr, const ExpandedObjectMethods *methods, MemoryContext obj_context)
Definition: expandeddatum.c:48
void DeleteExpandedObject(Datum d)
Definition: expandeddatum.c:136
Datum TransferExpandedObject(Datum d, MemoryContext new_parent)
Definition: expandeddatum.c:118
Datum MakeExpandedObjectReadOnlyInternal(Datum d)
Definition: expandeddatum.c:95
Size EOH_get_flat_size(ExpandedObjectHeader *eohptr)
Definition: expandeddatum.c:75
#define VARATT_IS_EXPANDED_HEADER(PTR)
Definition: expandeddatum.h:130
static Datum EOHPGetRWDatum(const struct ExpandedObjectHeader *eohptr)
Definition: expandeddatum.h:139
#define EOH_HEADER_MAGIC
Definition: expandeddatum.h:129
static Datum EOHPGetRODatum(const struct ExpandedObjectHeader *eohptr)
Definition: expandeddatum.h:145
Assert(PointerIsAligned(start, uint64))
void MemoryContextSetParent(MemoryContext context, MemoryContext new_parent)
Definition: mcxt.c:683
void MemoryContextDelete(MemoryContext context)
Definition: mcxt.c:469
uint64_t Datum
Definition: postgres.h:70
static Pointer DatumGetPointer(Datum X)
Definition: postgres.h:322
char eoh_rw_ptr[EXPANDED_POINTER_SIZE]
Definition: expandeddatum.h:112
MemoryContext eoh_context
Definition: expandeddatum.h:109
const ExpandedObjectMethods * eoh_methods
Definition: expandeddatum.h:106
char eoh_ro_ptr[EXPANDED_POINTER_SIZE]
Definition: expandeddatum.h:115
EOM_get_flat_size_method get_flat_size
Definition: expandeddatum.h:76
EOM_flatten_into_method flatten_into
Definition: expandeddatum.h:77
Definition: varatt.h:75
ExpandedObjectHeader * eohptr
Definition: varatt.h:76
Definition: varatt.h:150
static bool VARATT_IS_EXTERNAL_EXPANDED_RW(const void *PTR)
Definition: varatt.h:382
static char * VARDATA_EXTERNAL(const void *PTR)
Definition: varatt.h:340
static void SET_VARTAG_EXTERNAL(void *PTR, vartag_external tag)
Definition: varatt.h:453
static bool VARATT_IS_EXTERNAL_EXPANDED(const void *PTR)
Definition: varatt.h:389
@ VARTAG_EXPANDED_RW
Definition: varatt.h:88
@ VARTAG_EXPANDED_RO
Definition: varatt.h:87

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