getaddrinfo thread-safe?

[Joshua Rogers]

On 24/03/15 03:53, Carlos O'Donell wrote:
>>> >>                                         __have_o_nonblock
>>> >>                                           = (EXT(statp).nssocks[ns] == -1
>>> >>                                              && errno == EINVAL ? -1 : 1);
>> > And that is why it complains, probably.
>> > 
>> > Please check the vanilla glibc code.
> The code is still there, but you still need to show what is happening.
> Why does hellgrind think there is a race condition there, and does
> it make sense.
The reason helgrind is complaining is because __have_o_nonblock is being
set, but __have_o_nonblock is a global variable. So, if
__have_o_nonblock is overwritten by a different thread, the running
thread will use whatever the __have_o_nonblock is set to in the
"overwriting thread."
My guess is this will affect the connection that reopen makes, and will
make non-blocking a problem.

Another guess as to how to create a 'proof of concept', is by having the
threaded function randomly choose 1 or 0, and if 1, set nonblocking, and
if 0, don't choose nonblocking. Then do the getaddrinfo(), then monitor
if it sets it to non-blocking or not, and confirm that it does what it's
supposed to do.
However, I don't know how to do this.

The only place I can find reference to non-blocking getaddrinfo is here:
http://wiki.treck.com/getaddrinfo#Non-blocking_Mode which is not glibc.

I don't think I can do any more investigating, as I 1) don't know the
glibc code well enough, and 2) don't know helgrind/drd well enough. I've
just been reading from
http://valgrind.org/docs/manual/drd-manual.html#drd-manual.data-races



Thanks,


-- 
-- Joshua Rogers <https://internot.info/>

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: OpenPGP digital signature
URL: <http://sourceware.org/pipermail/libc-help/attachments/20150323/29ae86b3/attachment.sig>