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https://emptysqua.re/blog/getaddrinfo-deadlock/ claims that getaddrinfo may deadlock when using threads and fork on (amongst others) OSX due to using a global lock.
That lock is used when getaddrinfo is believed to be not thread safe, see the relevant code below (from the blog post):
/* On systems on which getaddrinfo() is believed to not be thread-safe,
 (this includes the getaddrinfo emulation) protect access with a lock. */
#if defined(WITH_THREAD) && (defined(__APPLE__) || \
 (defined(__FreeBSD__) && __FreeBSD_version+0 < 503000) || \
 defined(__OpenBSD__) || defined(__NetBSD__) || \
 defined(__VMS) || !defined(HAVE_GETADDRINFO))
#define USE_GETADDRINFO_LOCK
#endif
I think it is worthwhile to investigate whether or not getaddrinfo on OSX is really not thread safe. 
Some source code for OSX can be found at the link below, I haven't checked yet which OSX release this corresponds to:
http://www.opensource.apple.com/source/Libinfo/Libinfo-278/lookup.subproj/getaddrinfo.c