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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) 1996-2017, 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  */
30 {
32  varatt_expanded ptr;
33 
35  memcpy(&ptr, VARDATA_EXTERNAL(datum), sizeof(ptr));
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
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 
61  memcpy(VARDATA_EXTERNAL(eohptr->eoh_rw_ptr), &ptr, sizeof(ptr));
62 
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
76 {
77  return (*eohptr->eoh_methods->get_flat_size) (eohptr);
78 }
79 
80 void
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
96 {
97  ExpandedObjectHeader *eohptr;
98 
99  /* Nothing to do if not a read-write expanded-object pointer */
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
119 {
120  ExpandedObjectHeader *eohptr = DatumGetEOHP(d);
121 
122  /* Assert caller gave a R/W pointer */
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
137 {
138  ExpandedObjectHeader *eohptr = DatumGetEOHP(d);
139 
140  /* Assert caller gave a R/W pointer */
142 
143  /* Kill it */
145 }
ExpandedObjectHeader * eohptr
Definition: postgres.h:104
void MemoryContextDelete(MemoryContext context)
Definition: mcxt.c:200
EOM_get_flat_size_method get_flat_size
Definition: expandeddatum.h:74
Datum MakeExpandedObjectReadOnlyInternal(Datum d)
Definition: expandeddatum.c:95
#define VARATT_IS_EXTERNAL_EXPANDED(PTR)
Definition: postgres.h:323
void MemoryContextSetParent(MemoryContext context, MemoryContext new_parent)
Definition: mcxt.c:317
char eoh_rw_ptr[EXPANDED_POINTER_SIZE]
return result
Definition: formatting.c:1633
#define VARDATA_EXTERNAL(PTR)
Definition: postgres.h:311
Datum TransferExpandedObject(Datum d, MemoryContext new_parent)
#define SET_VARTAG_EXTERNAL(PTR, tag)
Definition: postgres.h:332
#define EOH_HEADER_MAGIC
void EOH_init_header(ExpandedObjectHeader *eohptr, const ExpandedObjectMethods *methods, MemoryContext obj_context)
Definition: expandeddatum.c:48
EOM_flatten_into_method flatten_into
Definition: expandeddatum.h:75
const ExpandedObjectMethods * eoh_methods
Size EOH_get_flat_size(ExpandedObjectHeader *eohptr)
Definition: expandeddatum.c:75
ExpandedObjectHeader * DatumGetEOHP(Datum d)
Definition: expandeddatum.c:29
char eoh_ro_ptr[EXPANDED_POINTER_SIZE]
uintptr_t Datum
Definition: postgres.h:372
void EOH_flatten_into(ExpandedObjectHeader *eohptr, void *result, Size allocated_size)
Definition: expandeddatum.c:81
void DeleteExpandedObject(Datum d)
#define Assert(condition)
Definition: c.h:675
#define EOHPGetRODatum(eohptr)
size_t Size
Definition: c.h:356
#define VARATT_IS_EXPANDED_HEADER(PTR)
#define DatumGetPointer(X)
Definition: postgres.h:555
#define EOHPGetRWDatum(eohptr)
#define VARATT_IS_EXTERNAL_EXPANDED_RW(PTR)
Definition: postgres.h:321
MemoryContext eoh_context