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/*-------------------------------------------------------------------------
*
* expandeddatum.c
* Support functions for "expanded" value representations.
*
* Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/utils/adt/expandeddatum.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "utils/expandeddatum.h"
#include "utils/memutils.h"
/*
* DatumGetEOHP
*
* Given a Datum that is an expanded-object reference, extract the pointer.
*
* This is a bit tedious since the pointer may not be properly aligned;
* compare VARATT_EXTERNAL_GET_POINTER().
*/
ExpandedObjectHeader *
DatumGetEOHP(Datum d)
{
varattrib_1b_e *datum = (varattrib_1b_e *) DatumGetPointer(d);
varatt_expanded ptr;
Assert(VARATT_IS_EXTERNAL_EXPANDED(datum));
memcpy(&ptr, VARDATA_EXTERNAL(datum), sizeof(ptr));
Assert(VARATT_IS_EXPANDED_HEADER(ptr.eohptr));
return ptr.eohptr;
}
/*
* EOH_init_header
*
* Initialize the common header of an expanded object.
*
* The main thing this encapsulates is initializing the TOAST pointers.
*/
void
EOH_init_header(ExpandedObjectHeader *eohptr,
const ExpandedObjectMethods *methods,
MemoryContext obj_context)
{
varatt_expanded ptr;
eohptr->vl_len_ = EOH_HEADER_MAGIC;
eohptr->eoh_methods = methods;
eohptr->eoh_context = obj_context;
ptr.eohptr = eohptr;
SET_VARTAG_EXTERNAL(eohptr->eoh_rw_ptr, VARTAG_EXPANDED_RW);
memcpy(VARDATA_EXTERNAL(eohptr->eoh_rw_ptr), &ptr, sizeof(ptr));
SET_VARTAG_EXTERNAL(eohptr->eoh_ro_ptr, VARTAG_EXPANDED_RO);
memcpy(VARDATA_EXTERNAL(eohptr->eoh_ro_ptr), &ptr, sizeof(ptr));
}
/*
* EOH_get_flat_size
* EOH_flatten_into
*
* Convenience functions for invoking the "methods" of an expanded object.
*/
Size
EOH_get_flat_size(ExpandedObjectHeader *eohptr)
{
return eohptr->eoh_methods->get_flat_size(eohptr);
}
void
EOH_flatten_into(ExpandedObjectHeader *eohptr,
void *result, Size allocated_size)
{
eohptr->eoh_methods->flatten_into(eohptr, result, allocated_size);
}
/*
* If the Datum represents a R/W expanded object, change it to R/O.
* Otherwise return the original Datum.
*
* Caller must ensure that the datum is a non-null varlena value. Typically
* this is invoked via MakeExpandedObjectReadOnly(), which checks that.
*/
Datum
MakeExpandedObjectReadOnlyInternal(Datum d)
{
ExpandedObjectHeader *eohptr;
/* Nothing to do if not a read-write expanded-object pointer */
if (!VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(d)))
return d;
/* Now safe to extract the object pointer */
eohptr = DatumGetEOHP(d);
/* Return the built-in read-only pointer instead of given pointer */
return EOHPGetRODatum(eohptr);
}
/*
* Transfer ownership of an expanded object to a new parent memory context.
* The object must be referenced by a R/W pointer, and what we return is
* always its "standard" R/W pointer, which is certain to have the same
* lifespan as the object itself. (The passed-in pointer might not, and
* in any case wouldn't provide a unique identifier if it's not that one.)
*/
Datum
TransferExpandedObject(Datum d, MemoryContext new_parent)
{
ExpandedObjectHeader *eohptr = DatumGetEOHP(d);
/* Assert caller gave a R/W pointer */
Assert(VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(d)));
/* Transfer ownership */
MemoryContextSetParent(eohptr->eoh_context, new_parent);
/* Return the object's standard read-write pointer */
return EOHPGetRWDatum(eohptr);
}
/*
* Delete an expanded object (must be referenced by a R/W pointer).
*/
void
DeleteExpandedObject(Datum d)
{
ExpandedObjectHeader *eohptr = DatumGetEOHP(d);
/* Assert caller gave a R/W pointer */
Assert(VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(d)));
/* Kill it */
MemoryContextDelete(eohptr->eoh_context);
}
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