146 lines
3.8 KiB
C
146 lines
3.8 KiB
C
/*-------------------------------------------------------------------------
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*
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* expandeddatum.c
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* Support functions for "expanded" value representations.
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*
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* Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* src/backend/utils/adt/expandeddatum.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "utils/expandeddatum.h"
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#include "utils/memutils.h"
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/*
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* DatumGetEOHP
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*
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* Given a Datum that is an expanded-object reference, extract the pointer.
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*
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* This is a bit tedious since the pointer may not be properly aligned;
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* compare VARATT_EXTERNAL_GET_POINTER().
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*/
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ExpandedObjectHeader *
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DatumGetEOHP(Datum d)
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{
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varattrib_1b_e *datum = (varattrib_1b_e *) DatumGetPointer(d);
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varatt_expanded ptr;
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Assert(VARATT_IS_EXTERNAL_EXPANDED(datum));
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memcpy(&ptr, VARDATA_EXTERNAL(datum), sizeof(ptr));
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Assert(VARATT_IS_EXPANDED_HEADER(ptr.eohptr));
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return ptr.eohptr;
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}
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/*
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* EOH_init_header
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*
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* Initialize the common header of an expanded object.
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*
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* The main thing this encapsulates is initializing the TOAST pointers.
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*/
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void
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EOH_init_header(ExpandedObjectHeader *eohptr,
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const ExpandedObjectMethods *methods,
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MemoryContext obj_context)
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{
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varatt_expanded ptr;
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eohptr->vl_len_ = EOH_HEADER_MAGIC;
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eohptr->eoh_methods = methods;
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eohptr->eoh_context = obj_context;
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ptr.eohptr = eohptr;
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SET_VARTAG_EXTERNAL(eohptr->eoh_rw_ptr, VARTAG_EXPANDED_RW);
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memcpy(VARDATA_EXTERNAL(eohptr->eoh_rw_ptr), &ptr, sizeof(ptr));
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SET_VARTAG_EXTERNAL(eohptr->eoh_ro_ptr, VARTAG_EXPANDED_RO);
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memcpy(VARDATA_EXTERNAL(eohptr->eoh_ro_ptr), &ptr, sizeof(ptr));
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}
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/*
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* EOH_get_flat_size
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* EOH_flatten_into
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*
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* Convenience functions for invoking the "methods" of an expanded object.
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*/
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Size
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EOH_get_flat_size(ExpandedObjectHeader *eohptr)
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{
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return eohptr->eoh_methods->get_flat_size(eohptr);
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}
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void
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EOH_flatten_into(ExpandedObjectHeader *eohptr,
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void *result, Size allocated_size)
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{
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eohptr->eoh_methods->flatten_into(eohptr, result, allocated_size);
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}
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/*
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* If the Datum represents a R/W expanded object, change it to R/O.
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* Otherwise return the original Datum.
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*
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* Caller must ensure that the datum is a non-null varlena value. Typically
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* this is invoked via MakeExpandedObjectReadOnly(), which checks that.
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*/
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Datum
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MakeExpandedObjectReadOnlyInternal(Datum d)
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{
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ExpandedObjectHeader *eohptr;
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/* Nothing to do if not a read-write expanded-object pointer */
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if (!VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(d)))
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return d;
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/* Now safe to extract the object pointer */
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eohptr = DatumGetEOHP(d);
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/* Return the built-in read-only pointer instead of given pointer */
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return EOHPGetRODatum(eohptr);
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}
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/*
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* Transfer ownership of an expanded object to a new parent memory context.
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* The object must be referenced by a R/W pointer, and what we return is
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* always its "standard" R/W pointer, which is certain to have the same
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* lifespan as the object itself. (The passed-in pointer might not, and
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* in any case wouldn't provide a unique identifier if it's not that one.)
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*/
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Datum
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TransferExpandedObject(Datum d, MemoryContext new_parent)
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{
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ExpandedObjectHeader *eohptr = DatumGetEOHP(d);
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/* Assert caller gave a R/W pointer */
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Assert(VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(d)));
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/* Transfer ownership */
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MemoryContextSetParent(eohptr->eoh_context, new_parent);
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/* Return the object's standard read-write pointer */
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return EOHPGetRWDatum(eohptr);
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}
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/*
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* Delete an expanded object (must be referenced by a R/W pointer).
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*/
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void
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DeleteExpandedObject(Datum d)
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{
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ExpandedObjectHeader *eohptr = DatumGetEOHP(d);
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/* Assert caller gave a R/W pointer */
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Assert(VARATT_IS_EXTERNAL_EXPANDED_RW(DatumGetPointer(d)));
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/* Kill it */
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MemoryContextDelete(eohptr->eoh_context);
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}
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