|From:||Jan Urbański <wulczer(at)wulczer(dot)org>|
|To:||Andres Freund <andres(at)2ndquadrant(dot)com>|
|Cc:||Pg Hackers <pgsql-hackers(at)postgresql(dot)org>|
|Subject:||Re: libpq's multi-threaded SSL callback handling is busted|
|Views:||Raw Message | Whole Thread | Download mbox | Resend email|
Jan Urbański writes:
> Andres Freund writes:
>> On 2015-02-12 09:31:27 +0100, Jan Urbański wrote:
>>> That doesn't solve the problem of the Python deadlock, where you're not at
>>> leisure to call a C function at the beginning of your module.
>> We could just never unload the hooks...
> That's what we did before 4e816286533dd34c10b368487d4079595a3e1418 :) And it
> got changed after http://firstname.lastname@example.org
>>> > * If there's already callbacks set: Remember that fact and don't
>>> > overwrite. In the next major version: warn.
>>> So yeah, that was my initial approach - check if callbacks are set, don't do
>>> the dance if they are. It felt like a crutch, though, and racy at that. There's
>>> no atomic way to test-and-set those callbacks. The window for racyness is
>>> small, though.
>> If you do that check during library initialization instead of every
>> connection it shouldn't be racy - if that part is run in a multithreaded
>> fashion you're doing something crazy.
> Yes, that's true. The problem is that there's no real libpq initialisation
> function. The docs say that:
> "If your application initializes libssl and/or libcrypto libraries and libpq is
> built with SSL support, you should call PQinitOpenSSL"
> So most apps will just not bother. The moment you know you'll need SSL is only
> when you get an 'S' message from the server...
For the sake of discussion, here's a patch to prevent stomping on
previously-set callbacks, racy as it looks.
FWIW, it does fix the Python deadlock and doesn't cause the PHP segfault...
|Next Message||Robert Haas||2015-02-12 12:40:12||Re: assessing parallel-safety|
|Previous Message||Jan Urbański||2015-02-12 11:43:08||Re: libpq's multi-threaded SSL callback handling is busted|