C Function Memory Management

Hello

2012/12/12 Martin French <Martin.French@romaxtech.com>:

Ok, so just a (hopefully) quick question.

I know that I should be using the Postgres function palloc in place of
malloc, but what about realloc? Is there an equivalent?

yes,

repalloc

Regards

Pavel Stehule

Thanks.
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Hi Pavel

yes,

repalloc

Maybe I should've looked a little harder for that one! Ha Ha!

I assume it's an exact functional copy of realloc, and see where I get
with it!

Many Thanks.
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Martin French <Martin.French@romaxtech.com> writes:

repalloc

Maybe I should've looked a little harder for that one! Ha Ha!

I assume it's an exact functional copy of realloc, and see where I get
with it!

One thing to know about it is that repalloc re-sizes the given chunk
while keeping it in the same memory context it was originally allocated
in (ie, CurrentMemoryContext doesn't matter). This may not matter much
if you're only dealing with allocations that just live as long as the
current function call --- but if you're trying to preserve data across
calls, it's critical to know.

regards, tom lane

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One thing to know about it is that repalloc re-sizes the given chunk
while keeping it in the same memory context it was originally allocated
in (ie, CurrentMemoryContext doesn't matter). This may not matter much
if you're only dealing with allocations that just live as long as the
current function call --- but if you're trying to preserve data across
calls, it's critical to know.

regards, tom lane

Thanks for this Tom, I'll keep that in mind for future functions.

In this particular implementation, it's not necessary to preserve the data
once the function is complete.

So out of curiosity, what would be your approach for data preservation
cross call?

Cheers

Martin
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Martin French <Martin.French@romaxtech.com> writes:

So out of curiosity, what would be your approach for data preservation
cross call?

Usually I'd allocate the space in fcinfo->flinfo->fn_mcxt (which is a
query-lifespan context) and keep a pointer to it in
fcinfo->flinfo->fn_extra (which is a void * field that a C function
can do what it pleases with). There are plenty of examples in the
Postgres source code. If you are looking to cache data longer than
one query then it takes more thought.

regards, tom lane

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Usually I'd allocate the space in fcinfo->flinfo->fn_mcxt (which is a
query-lifespan context) and keep a pointer to it in
fcinfo->flinfo->fn_extra (which is a void * field that a C function
can do what it pleases with). There are plenty of examples in the
Postgres source code. If you are looking to cache data longer than
one query then it takes more thought.

regards, tom lane

Thanks Tom. I'll have a look into this when I have more time.

Kind Regards.

Martin.
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