2 Replies
      Latest reply on Oct 20, 2016 3:01 AM by granada29
      granada29 Level 1 Level 1 (0 points)

        I am making concurrent calls to getnameinfo() by submitting each call to a separate dispatch_queue.


        If there is some problem or slowness in a dns lookup I would like to cancel that call before the default timeout (30 secs?) has passed.


        Is it possible to raise SIGALRM to target a specific dispatch_queue in order to interrupt whatever system call getnameinfo() is hanging on. The dispatch_sources approach seems to invoke the signal handler from a specified queue but I'm not sure which of my dispatch queues will actually receive the interrupt.


        Or is there some other sneaky way to cause getnameinfo() to return early.


        Sorry if this is not the correct forum, but I am currently working with Swift and managing my dispatch_queues from Swift.




        • Re: Cancelling a call to getnameinfo()
          eskimo Apple Staff Apple Staff (13,335 points)

          There’s no way you can reasonably cancel getnameinfo.  Trust me, signals are not the answer (signals are never the answer :-)

          The underlying DNS implementation on Apple platforms is fully async and does support cancellation.  The problem here is that BSD APIs don’t expose that support.

          Are you doing anything special with getnameinfo?  In typical uses cases you can get equivalent behaviour by moving ‘up’ to CFHost, a type that does support async operations.  CFHost isn’t a lot of fun to call from Swift; post back if you get stuck.

          If you need more control you can drop ‘down’ to <dns_sd.h>, but that’s less fun because you have to monkey with DNS records directly (there is an equivalent to getaddrinfo, namely DNSServiceGetAddrInfo, but not for getnameinfo).

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