07.06.2023 15:53, Robert Haas wrote:
Right now, if you need a bit
of additional session-local state, you just declare a variable and
you're all set. That's not a perfect system and does cause some
problems, but we can't go from there to a system where it's impossible
to add session-local state without hacking core.
or else it needs to
be design in some kind of extensible way that doesn't require it to
know the full details of every sort of object that's being used as
session-local state anywhere in the system.
And it is quite possible. Although with indirection involved.
For example, we want to add session variable "my_hello_var".
We first need to declare "offset variable".
Then register it in a session.
And then use function and/or macros to get actual address:
/* session.h */
extern size_t RegisterSessionVar(size_t size);
extern void* CurSessionVar(size_t offset);
/* session.c */
typedef struct Session {
char *vars;
} Session;
static _Thread_local Session* curSession;
static size_t sessionVarsSize = 0;
size_t
RegisterSessionVar(size_t size)
{
size_t off = sessionVarsSize;
sessionVarsSize += size;
return off;
}
void*
CurSession(size_t offset)
{
return curSession->vars + offset;
}
/* module_internal.h */
typedef int my_hello_var_t;
extern size_t my_hello_var_offset;
/* access macros */
#define my_hello_var
(*(my_hello_var_t*)(CurSessionVar(my_hello_var_offset)))
/* module.c */
size_t my_hello_var_offset = 0;
void
PG_init() {
RegisterSessionVar(sizeof(my_hello_var_t), &my_hello_var_offset);
}
For security reasons, offset could be mangled.
------
regards,
Yura Sokolov
