[Python-Dev] Re: Re: mysterious hangs in socket code

[Mats Wichmann]

Martin:

 >I think that part is already settled: getaddrinfo, on Linux, is
 >thread-safe.

The latest Posix/Single UNIX spec in fact require getaddrinfo
(and getnameinfo) to be thread-safe.

and Guido:

 >I tried to read the glibc getaddrinfo() source, but it looks like it
 >would be a term project...  It could be that it's just doing a lot
 >more interaction with a DNS server.
 >
 >I believe that Jeremy suspects that the test program isn't just slow,
 >but that one slow thread actually blocks all other threads from making
 >progress.  If that's the case (we don't know for sure), we're looking
 >for a bottleneck in the getaddrinfo() code that somehow holds a
 >resource needed by all threads calling getaddrinfo().

Gives me a headache, too, especially once it vectors off into
the glibc nss code.  These routines (__gethostbyname2_r is the
likely suspect, __gethostbyaddr_r and __getservbyname_r might
also get called) do have paths that could twiddle a glibc internal
lock so it's not impossible there's an issue here, although at
something less than a term-paper-depth look it doesn't SEEM like
it should ever be able to block for very long.