Re: Static memory, shared memory

Jack Orenstein <jao(at)geophile(dot)com> writes:
> I am writing a Postgres extension, and thought that I had memory
> corruption, (thanks for the --enable-cassert lead). I might, but It now
> looks like I need to understand the use of shared memory and locking in
> Postgres. So I have two questions.

> 1) I am now guessing that my original problem is caused by relying on
> static memory in my extension (i.e., in the source declaring
> PG_MODULE_MAGIC). This static memory is almost but not quite constant -- it
> is initialized from _PG_init, and then never modified. I suspect that this
> cannot work in general (since Postgres is multi-process), but I thought it
> would be adequate for early development. However, I am seeing this static
> memory get corrupted even when there is only a single process executing the
> extension code (verified by examining getpid()).

Define what you mean by "corrupted". It seems highly unlikely that any
code but your own is touching this memory.

Really the big-picture question here is what are you hoping to accomplish
and why do you think this memory might need to be shared?

regards, tom lane