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Recommend wrappers of PG_DETOAST_DATUM_PACKED().

Browse Source 
When commit 3e23b68dac introduced
single-byte varlena headers, its fmgr.h changes presented
PG_GETARG_TEXT_PP() and PG_GETARG_TEXT_P() as equals.  Its postgres.h
changes presented PG_DETOAST_DATUM_PACKED() and VARDATA_ANY() as the
exceptional case.  Now, instead, firmly recommend PG_GETARG_TEXT_PP()
over PG_GETARG_TEXT_P(); likewise for other ...PP() macros.  This shaves
cycles and invites consistency of style.
This commit is contained in:
Noah Misch 2017-03-12 19:35:33 -04:00
parent 944a026b4e
commit 9d7726c2ba
6 changed files with 74 additions and 57 deletions
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32
doc/src/sgml/xfunc.sgml
View File

@ -2388,18 +2388,23 @@ PG_FUNCTION_INFO_V1(copytext);
Datum
copytext(PG_FUNCTION_ARGS)
{
text *t = PG_GETARG_TEXT_P(0);
text *t = PG_GETARG_TEXT_PP(0);
/*
* VARSIZE is the total size of the struct in bytes.
* VARSIZE_ANY_EXHDR is the size of the struct in bytes, minus the
* VARHDRSZ or VARHDRSZ_SHORT of its header. Construct the copy with a
* full-length header.
*/
text *new_t = (text *) palloc(VARSIZE(t));
SET_VARSIZE(new_t, VARSIZE(t));
text *new_t = (text *) palloc(VARSIZE_ANY_EXHDR(t) + VARHDRSZ);
SET_VARSIZE(new_t, VARSIZE_ANY_EXHDR(t) + VARHDRSZ);
/*
* VARDATA is a pointer to the data region of the struct.
* VARDATA is a pointer to the data region of the new struct. The source
* could be a short datum, so retrieve its data through VARDATA_ANY.
*/
memcpy((void *) VARDATA(new_t), /* destination */
(void *) VARDATA(t), /* source */
VARSIZE(t) - VARHDRSZ); /* how many bytes */
(void *) VARDATA_ANY(t), /* source */
VARSIZE_ANY_EXHDR(t)); /* how many bytes */
PG_RETURN_TEXT_P(new_t);
}
@ -2408,15 +2413,16 @@ PG_FUNCTION_INFO_V1(concat_text);
Datum
concat_text(PG_FUNCTION_ARGS)
{
text *arg1 = PG_GETARG_TEXT_P(0);
text *arg2 = PG_GETARG_TEXT_P(1);
int32 new_text_size = VARSIZE(arg1) + VARSIZE(arg2) - VARHDRSZ;
text *arg1 = PG_GETARG_TEXT_PP(0);
text *arg2 = PG_GETARG_TEXT_PP(1);
int32 arg1_size = VARSIZE_ANY_EXHDR(arg1);
int32 arg2_size = VARSIZE_ANY_EXHDR(arg2);
int32 new_text_size = arg1_size + arg2_size + VARHDRSZ;
text *new_text = (text *) palloc(new_text_size);
SET_VARSIZE(new_text, new_text_size);
memcpy(VARDATA(new_text), VARDATA(arg1), VARSIZE(arg1) - VARHDRSZ);
memcpy(VARDATA(new_text) + (VARSIZE(arg1) - VARHDRSZ),
VARDATA(arg2), VARSIZE(arg2) - VARHDRSZ);
memcpy(VARDATA(new_text), VARDATA_ANY(arg1), arg1_size);
memcpy(VARDATA(new_text) + arg1_size, VARDATA_ANY(arg2), arg2_size);
PG_RETURN_TEXT_P(new_text);
}
]]>

9
src/include/c.h
View File

@ -429,10 +429,11 @@ typedef struct
* may be compressed or moved out-of-line. However datatype-specific routines
* are mostly content to deal with de-TOASTed values only, and of course
* client-side routines should never see a TOASTed value. But even in a
* de-TOASTed value, beware of touching vl_len_ directly, as its representation
* is no longer convenient. It's recommended that code always use the VARDATA,
* VARSIZE, and SET_VARSIZE macros instead of relying on direct mentions of
* the struct fields. See postgres.h for details of the TOASTed form.
* de-TOASTed value, beware of touching vl_len_ directly, as its
* representation is no longer convenient. It's recommended that code always
* use macros VARDATA_ANY, VARSIZE_ANY, VARSIZE_ANY_EXHDR, VARDATA, VARSIZE,
* and SET_VARSIZE instead of relying on direct mentions of the struct fields.
* See postgres.h for details of the TOASTed form.
* ----------------
*/
struct varlena

34
src/include/fmgr.h
View File

@ -178,11 +178,12 @@ extern void fmgr_info_copy(FmgrInfo *dstinfo, FmgrInfo *srcinfo,
* The resulting datum can be accessed using VARSIZE_ANY() and VARDATA_ANY()
* (beware of multiple evaluations in those macros!)
*
* WARNING: It is only safe to use pg_detoast_datum_packed() and
* VARDATA_ANY() if you really don't care about the alignment. Either because
* you're working with something like text where the alignment doesn't matter
* or because you're not going to access its constituent parts and just use
* things like memcpy on it anyways.
* In consumers oblivious to data alignment, call PG_DETOAST_DATUM_PACKED(),
* VARDATA_ANY(), VARSIZE_ANY() and VARSIZE_ANY_EXHDR(). Elsewhere, call
* PG_DETOAST_DATUM(), VARDATA() and VARSIZE(). Directly fetching an int16,
* int32 or wider field in the struct representing the datum layout requires
* aligned data. memcpy() is alignment-oblivious, as are most operations on
* datatypes, such as text, whose layout struct contains only char fields.
*
* Note: it'd be nice if these could be macros, but I see no way to do that
* without evaluating the arguments multiple times, which is NOT acceptable.
@ -243,13 +244,9 @@ extern struct varlena *pg_detoast_datum_packed(struct varlena * datum);
/* and this if you can handle 1-byte-header datums: */
#define PG_GETARG_VARLENA_PP(n) PG_DETOAST_DATUM_PACKED(PG_GETARG_DATUM(n))
/* DatumGetFoo macros for varlena types will typically look like this: */
#define DatumGetByteaP(X) ((bytea *) PG_DETOAST_DATUM(X))
#define DatumGetByteaPP(X) ((bytea *) PG_DETOAST_DATUM_PACKED(X))
#define DatumGetTextP(X) ((text *) PG_DETOAST_DATUM(X))
#define DatumGetTextPP(X) ((text *) PG_DETOAST_DATUM_PACKED(X))
#define DatumGetBpCharP(X) ((BpChar *) PG_DETOAST_DATUM(X))
#define DatumGetBpCharPP(X) ((BpChar *) PG_DETOAST_DATUM_PACKED(X))
#define DatumGetVarCharP(X) ((VarChar *) PG_DETOAST_DATUM(X))
#define DatumGetVarCharPP(X) ((VarChar *) PG_DETOAST_DATUM_PACKED(X))
#define DatumGetHeapTupleHeader(X) ((HeapTupleHeader) PG_DETOAST_DATUM(X))
/* And we also offer variants that return an OK-to-write copy */
@ -264,13 +261,9 @@ extern struct varlena *pg_detoast_datum_packed(struct varlena * datum);
#define DatumGetBpCharPSlice(X,m,n) ((BpChar *) PG_DETOAST_DATUM_SLICE(X,m,n))
#define DatumGetVarCharPSlice(X,m,n) ((VarChar *) PG_DETOAST_DATUM_SLICE(X,m,n))
/* GETARG macros for varlena types will typically look like this: */
#define PG_GETARG_BYTEA_P(n) DatumGetByteaP(PG_GETARG_DATUM(n))
#define PG_GETARG_BYTEA_PP(n) DatumGetByteaPP(PG_GETARG_DATUM(n))
#define PG_GETARG_TEXT_P(n) DatumGetTextP(PG_GETARG_DATUM(n))
#define PG_GETARG_TEXT_PP(n) DatumGetTextPP(PG_GETARG_DATUM(n))
#define PG_GETARG_BPCHAR_P(n) DatumGetBpCharP(PG_GETARG_DATUM(n))
#define PG_GETARG_BPCHAR_PP(n) DatumGetBpCharPP(PG_GETARG_DATUM(n))
#define PG_GETARG_VARCHAR_P(n) DatumGetVarCharP(PG_GETARG_DATUM(n))
#define PG_GETARG_VARCHAR_PP(n) DatumGetVarCharPP(PG_GETARG_DATUM(n))
#define PG_GETARG_HEAPTUPLEHEADER(n) DatumGetHeapTupleHeader(PG_GETARG_DATUM(n))
/* And we also offer variants that return an OK-to-write copy */
@ -284,6 +277,21 @@ extern struct varlena *pg_detoast_datum_packed(struct varlena * datum);
#define PG_GETARG_TEXT_P_SLICE(n,a,b) DatumGetTextPSlice(PG_GETARG_DATUM(n),a,b)
#define PG_GETARG_BPCHAR_P_SLICE(n,a,b) DatumGetBpCharPSlice(PG_GETARG_DATUM(n),a,b)
#define PG_GETARG_VARCHAR_P_SLICE(n,a,b) DatumGetVarCharPSlice(PG_GETARG_DATUM(n),a,b)
/*
* Obsolescent variants that guarantee INT alignment for the return value.
* Few operations on these particular types need alignment, mainly operations
* that cast the VARDATA pointer to a type like int16[]. Most code should use
* the ...PP(X) counterpart. Nonetheless, these appear frequently in code
* predating the PostgreSQL 8.3 introduction of the ...PP(X) variants.
*/
#define DatumGetByteaP(X) ((bytea *) PG_DETOAST_DATUM(X))
#define DatumGetTextP(X) ((text *) PG_DETOAST_DATUM(X))
#define DatumGetBpCharP(X) ((BpChar *) PG_DETOAST_DATUM(X))
#define DatumGetVarCharP(X) ((VarChar *) PG_DETOAST_DATUM(X))
#define PG_GETARG_BYTEA_P(n) DatumGetByteaP(PG_GETARG_DATUM(n))
#define PG_GETARG_TEXT_P(n) DatumGetTextP(PG_GETARG_DATUM(n))
#define PG_GETARG_BPCHAR_P(n) DatumGetBpCharP(PG_GETARG_DATUM(n))
#define PG_GETARG_VARCHAR_P(n) DatumGetVarCharP(PG_GETARG_DATUM(n))
/* To return a NULL do this: */
#define PG_RETURN_NULL() \

22
src/include/postgres.h
View File

@ -287,20 +287,18 @@ typedef struct
/* Externally visible macros */
/*
* VARDATA, VARSIZE, and SET_VARSIZE are the recommended API for most code
* for varlena datatypes. Note that they only work on untoasted,
* 4-byte-header Datums!
* In consumers oblivious to data alignment, call PG_DETOAST_DATUM_PACKED(),
* VARDATA_ANY(), VARSIZE_ANY() and VARSIZE_ANY_EXHDR(). Elsewhere, call
* PG_DETOAST_DATUM(), VARDATA() and VARSIZE(). Directly fetching an int16,
* int32 or wider field in the struct representing the datum layout requires
* aligned data. memcpy() is alignment-oblivious, as are most operations on
* datatypes, such as text, whose layout struct contains only char fields.
*
* Code that wants to use 1-byte-header values without detoasting should
* use VARSIZE_ANY/VARSIZE_ANY_EXHDR/VARDATA_ANY. The other macros here
* should usually be used only by tuple assembly/disassembly code and
* code that specifically wants to work with still-toasted Datums.
* Code assembling a new datum should call VARDATA() and SET_VARSIZE().
* (Datums begin life untoasted.)
*
* WARNING: It is only safe to use VARDATA_ANY() -- typically with
* PG_DETOAST_DATUM_PACKED() -- if you really don't care about the alignment.
* Either because you're working with something like text where the alignment
* doesn't matter or because you're not going to access its constituent parts
* and just use things like memcpy on it anyways.
* Other macros here should usually be used only by tuple assembly/disassembly
* code and code that specifically wants to work with still-toasted Datums.
*/
#define VARDATA(PTR) VARDATA_4B(PTR)
#define VARSIZE(PTR) VARSIZE_4B(PTR)

5
src/include/utils/inet.h
View File

@ -104,12 +104,13 @@ typedef struct macaddr
/*
* fmgr interface macros
*/
#define DatumGetInetP(X) ((inet *) PG_DETOAST_DATUM(X))
#define DatumGetInetPP(X) ((inet *) PG_DETOAST_DATUM_PACKED(X))
#define InetPGetDatum(X) PointerGetDatum(X)
#define PG_GETARG_INET_P(n) DatumGetInetP(PG_GETARG_DATUM(n))
#define PG_GETARG_INET_PP(n) DatumGetInetPP(PG_GETARG_DATUM(n))
#define PG_RETURN_INET_P(x) return InetPGetDatum(x)
/* obsolescent variants */
#define DatumGetInetP(X) ((inet *) PG_DETOAST_DATUM(X))
#define PG_GETARG_INET_P(n) DatumGetInetP(PG_GETARG_DATUM(n))
/* macaddr is a fixed-length pass-by-reference datatype */
#define DatumGetMacaddrP(X) ((macaddr *) DatumGetPointer(X))
#define MacaddrPGetDatum(X) PointerGetDatum(X)

29
src/tutorial/funcs_new.c
View File

@ -66,21 +66,24 @@ PG_FUNCTION_INFO_V1(copytext);
Datum
copytext(PG_FUNCTION_ARGS)
{
text *t = PG_GETARG_TEXT_P(0);
text *t = PG_GETARG_TEXT_PP(0);
/*
* VARSIZE is the total size of the struct in bytes.
* VARSIZE_ANY_EXHDR is the size of the struct in bytes, minus the
* VARHDRSZ or VARHDRSZ_SHORT of its header. Construct the copy with a
* full-length header.
*/
text *new_t = (text *) palloc(VARSIZE(t));
text *new_t = (text *) palloc(VARSIZE_ANY_EXHDR(t) + VARHDRSZ);
SET_VARSIZE(new_t, VARSIZE(t));
SET_VARSIZE(new_t, VARSIZE_ANY_EXHDR(t) + VARHDRSZ);
/*
* VARDATA is a pointer to the data region of the struct.
* VARDATA is a pointer to the data region of the new struct. The source
* could be a short datum, so retrieve its data through VARDATA_ANY.
*/
memcpy((void *) VARDATA(new_t), /* destination */
(void *) VARDATA(t), /* source */
VARSIZE(t) - VARHDRSZ); /* how many bytes */
(void *) VARDATA_ANY(t), /* source */
VARSIZE_ANY_EXHDR(t)); /* how many bytes */
PG_RETURN_TEXT_P(new_t);
}
@ -89,16 +92,16 @@ PG_FUNCTION_INFO_V1(concat_text);
Datum
concat_text(PG_FUNCTION_ARGS)
{
text *arg1 = PG_GETARG_TEXT_P(0);
text *arg2 = PG_GETARG_TEXT_P(1);
int32 arg1_size = VARSIZE(arg1) - VARHDRSZ;
int32 arg2_size = VARSIZE(arg2) - VARHDRSZ;
text *arg1 = PG_GETARG_TEXT_PP(0);
text *arg2 = PG_GETARG_TEXT_PP(1);
int32 arg1_size = VARSIZE_ANY_EXHDR(arg1);
int32 arg2_size = VARSIZE_ANY_EXHDR(arg2);
int32 new_text_size = arg1_size + arg2_size + VARHDRSZ;
text *new_text = (text *) palloc(new_text_size);
SET_VARSIZE(new_text, new_text_size);
memcpy(VARDATA(new_text), VARDATA(arg1), arg1_size);
memcpy(VARDATA(new_text) + arg1_size, VARDATA(arg2), arg2_size);
memcpy(VARDATA(new_text), VARDATA_ANY(arg1), arg1_size);
memcpy(VARDATA(new_text) + arg1_size, VARDATA_ANY(arg2), arg2_size);
PG_RETURN_TEXT_P(new_text);
}