Nathan Thatcher wrote:
So what options does that leave all of us who need to compile and run
our custom C functions in Windows?
After a bit of sleep and with the advantage of a now-working brain I've
got it working, at least with 8.3 .
The problem was with DLL linkage, especially the CurrentMemoryContext
global variable. I was defining BUILDING_DLL and using the PGDLLIMPORT
macro to export the copytext() function - but this was of course causing
everything in the Pg headers to be declared __declspec(dllexport)
instead of __declspec(dllimport) . AFAIK this is survivable for
functions, which will use a slower call thunk instead, but not for
exported variables.
As a result, MemoryContextAlloc(CurrentMemoryContext, (sz)) was being
called with a nonsensical pointer for CurrentMemoryContext and crashing.
To build the C function DLL correctly it correctly do not define the
BUILDING_DLL macro. Instead, define your own DLL export macros like:
#if defined(_MSC_VER) || defined(__MINGW32__)
#define COPYTEXT_EXPORT __declspec (dllexport)
#else
#define COPYTEXT_EXPORT
#endif
then declare your function as:
COPYTEXT_EXPORT Datum copytext2(PG_FUNCTION_ARGS) {
// blah blah
}
It should now be exported in the DLL's interface correctly AND have
correct access to Pg's exported functions and variables.
I did notice that I'm getting some warnings about inconsistent DLL
linkage for Pg_magic_func and pg_finfo_copytext . These really need to
be using __declspec(dllexport) rather than using __declspec(dllimport)
via PGDLLIMPORT .
Maybe it's worth providing a PGMODULEEXPORT macro for PG_MODULE_MAGIC,
PG_FUNCTION_INFO_V1, and for module writers to use to export their
functions in the DLL interface. A module author would have to ensure
that BUILDING_MODULE was defined.
Here's how the PG_MODULE_MAGIC and PG_FUNCTION_INFO_V1 macros would look:
/* This might want to go somewhere other than fmgr.h, like
* pg_config_os.h alongside the definition of PGDLLIMPORT
*/
#if defined(_MSC_VER) || defined(__MINGW32__)
#if defined(BUILDING_MODULE)
#define PGMODULEEXPORT __declspec (dllexport)
#else
// Never actually used
#define PGMODULEEXPORT __declspec (dllimport)
#endif
#else
#define PGMODULEEXPORT
#endif
#define PG_MODULE_MAGIC \
PGMODULEEXPORT Pg_magic_struct * \
PG_MAGIC_FUNCTION_NAME(void) \
{ \
static const Pg_magic_struct Pg_magic_data = PG_MODULE_MAGIC_DATA; \
return &Pg_magic_data; \
} \
extern int no_such_variable
#define PG_FUNCTION_INFO_V1(funcname) \
PGMODULEEXPORT const Pg_finfo_record * \
CppConcat(pg_finfo_,funcname) (void) \
{ \
static const Pg_finfo_record my_finfo = { 1 }; \
return &my_finfo; \
} \
extern int no_such_variable
I've tested this definition and it produces a DLL that links correctly
and does so without the warnings of inconsistent DLL linkage produced by
the original versions (which declared the function __declspec(dllimport)
then defined it).
Anyway, the C function examples need some changes to work correctly on
win32. I've attached updated versions. These redefine the
PG_MODULE_MAGIC and PG_FUNCTION_INFO_V1 macros, but if you omit that
code the module will still built, just with warnings, and will still work.
--
Craig Ringer
/*
* PostgreSQL example C functions.
*
* This file must be built as a shared library or dll and
* placed into the PostgreSQL `lib' directory. On Windows
* it must link to postgres.lib .
*
* postgresql/include/server must be on your header search path.
* With MSVC++ on win32 so must postgresql/include/server/port/win32_msvc .
* With MinGW use postgresql/include/server/port/win32 .
*/
#if defined(_MSC_VER) || defined(__MINGW32__)
#ifndef _USE_32BIT_TIME_T
#define _USE_32BIT_TIME_T
#endif
#endif
/* BUILDING_DLL causes the declarations in Pg's headers to be declared
* __declspec(dllexport) which will break DLL linkage. */
#ifdef BUILDING_DLL
#error Do not define BUILDING_DLL when building extension libraries
#endif
/* Ensure that Pg_module_function and friends are declared __declspec(dllexport) */
#ifndef BUILDING_MODULE
#define BUILDING_MODULE
#endif
#include "postgres.h"
#include <string.h>
#include "fmgr.h"
#include "utils/geo_decls.h"
/*--------------- BEGIN REDEFINITION OF PG MACROS -------------------
*
* These rewritten versions of PG_MODULE_MAGIC and PG_FUNCTION_INFO_V1
* declare the module functions as __declspec(dllexport) when building
* a module. They also provide PGMODULEEXPORT for exporting functions
* in user DLLs.
*/
#undef PG_MODULE_MAGIC
#undef PG_FUNCTION_INFO_V1
/* This might want to go somewhere other than fmgr.h, like
* pg_config_os.h alongside the definition of PGDLLIMPORT
*/
#if defined(_MSC_VER) || defined(__MINGW32__)
#if defined(BUILDING_MODULE)
#define PGMODULEEXPORT __declspec (dllexport)
#else
// Never actually used
#define PGMODULEEXPORT __declspec (dllimport)
#endif
#else
#define PGMODULEEXPORT
#endif
#define PG_MODULE_MAGIC \
PGMODULEEXPORT Pg_magic_struct * \
PG_MAGIC_FUNCTION_NAME(void) \
{ \
static const Pg_magic_struct Pg_magic_data = PG_MODULE_MAGIC_DATA; \
return &Pg_magic_data; \
} \
extern int no_such_variable
#define PG_FUNCTION_INFO_V1(funcname) \
PGMODULEEXPORT const Pg_finfo_record * \
CppConcat(pg_finfo_,funcname) (void) \
{ \
static const Pg_finfo_record my_finfo = { 1 }; \
return &my_finfo; \
} \
extern int no_such_variable
/*--------------- END REDEFINITION OF PG MACROS -------------------*/
PG_MODULE_MAGIC;
PG_FUNCTION_INFO_V1(add_one);
PGMODULEEXPORT Datum
add_one(PG_FUNCTION_ARGS)
{
int32 arg = PG_GETARG_INT32(0);
PG_RETURN_INT32(arg + 1);
}
/* by reference, fixed length */
PG_FUNCTION_INFO_V1(add_one_float8);
PGMODULEEXPORT Datum
add_one_float8(PG_FUNCTION_ARGS)
{
/* The macros for FLOAT8 hide its pass-by-reference nature. */
float8 arg = PG_GETARG_FLOAT8(0);
PG_RETURN_FLOAT8(arg + 1.0);
}
PG_FUNCTION_INFO_V1(makepoint);
PGMODULEEXPORT Datum
makepoint(PG_FUNCTION_ARGS)
{
/* Here, the pass-by-reference nature of Point is not hidden. */
Point *pointx = PG_GETARG_POINT_P(0);
Point *pointy = PG_GETARG_POINT_P(1);
Point *new_point = (Point *) palloc(sizeof(Point));
new_point->x = pointx->x;
new_point->y = pointy->y;
PG_RETURN_POINT_P(new_point);
}
/* by reference, variable length */
PG_FUNCTION_INFO_V1(copytext);
PGMODULEEXPORT Datum
copytext(PG_FUNCTION_ARGS)
{
text *t = PG_GETARG_TEXT_P(0);
/*
* VARSIZE is the total size of the struct in bytes.
*/
text *new_t = (text *) palloc(VARSIZE(t));
SET_VARSIZE(new_t, VARSIZE(t));
/*
* VARDATA is a pointer to the data region of the struct.
*/
memcpy((void *) VARDATA(new_t), /* destination */
(void *) VARDATA(t), /* source */
VARSIZE(t) - VARHDRSZ); /* how many bytes */
PG_RETURN_TEXT_P(new_t);
}
PG_FUNCTION_INFO_V1(concat_text);
PGMODULEEXPORT 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 *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);
PG_RETURN_TEXT_P(new_text);
}
