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Philip Withnall authored
res_query() uses global state in the form of the struct __res_state which contains the contents of resolv.conf (and other things). On Linux, this state seems to be thread-local, so there is no problem. On OS X, however, it is not, and hence multiple res_query() calls from parallel threads will compete and return bogus results. The fix for this is to use res_nquery(), introduced in BIND 8.2, which takes an explicit state argument. This allows us to manually store the state thread-locally. If res_nquery() isn’t available, we fall back to res_query(). It should be available on OS X though. As a data point, it’s available on Fedora 27. There’s a slight complication in the fact that OS X requires the state to be freed using res_ndestroy() rather than res_nclose(). Linux uses res_nclose(). (See, for example, the NetBSD man page: https://www.unix.com/man-page/netbsd/3/res_ninit/. The Linux one is incomplete and not so useful: http://ma...
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