Redundant DNS lookups

[alecmocatta]

Hyper's DNS resolver is spawning a bunch of blocking tasks to look up the same host, causing hundreds of blocking threads to be spawned. ~100 threads with the following stack cause cloudfront_logs to take ~20s to exit after returning from async fn main.

    2427 Thread_7871772: tokio-runtime-worker
    + 2427 thread_start  (in libsystem_pthread.dylib) + 13  [0x7fff63c2840d]
    +   2427 _pthread_start  (in libsystem_pthread.dylib) + 66  [0x7fff63c2c249]
    +     2427 _pthread_body  (in libsystem_pthread.dylib) + 126  [0x7fff63c292eb]
    +       2427 std::sys::unix::thread::Thread::new::thread_start::h545d31fdf79b3d9e  (in cloudfront_logs) + 45  [0x10d1eb3dd]  boxed.rs:1081
    +         2427 core::ops::function::FnOnce::call_once$u7b$$u7b$vtable.shim$u7d$$u7d$::h24d0ac9ca2e34eab  (in cloudfront_logs) + 17  [0x10d053ba1]  function.rs:233
    +           2427 std::thread::Builder::spawn_unchecked::_$u7b$$u7b$closure$u7d$$u7d$::h606d44b084314330  (in cloudfront_logs) + 278  [0x10d020416]  mod.rs:474
    +             2427 std::panic::catch_unwind::hf778b52e64c7dd68  (in cloudfront_logs) + 49  [0x10d01f391]  panic.rs:394
    +               2427 std::panicking::try::h0b8958571d7c7f99  (in cloudfront_logs) + 206  [0x10d05fb8e]  panicking.rs:325
    +                 2427 __rust_try  (in cloudfront_logs) + 29  [0x10d06454d]
    +                   2427 std::panicking::try::do_call::h417c11b07e629a5e  (in cloudfront_logs) + 95  [0x10d05fe8f]  panicking.rs:348
    +                     2427 _$LT$std..panic..AssertUnwindSafe$LT$F$GT$$u20$as$u20$core..ops..function..FnOnce$LT$$LP$$RP$$GT$$GT$::call_once::h6187c27ab70b5642  (in cloudfront_logs) + 49  [0x10d01efa1]  panic.rs:318
    +                       2427 std::thread::Builder::spawn_unchecked::_$u7b$$u7b$closure$u7d$$u7d$::_$u7b$$u7b$closure$u7d$$u7d$::ha5c6d4cb1a10bf6f  (in cloudfront_logs) + 49  [0x10d0205c1]  mod.rs:475
    +                         2427 std::sys_common::backtrace::__rust_begin_short_backtrace::h3308c5c2d8decb9c  (in cloudfront_logs) + 49  [0x10cff0371]  backtrace.rs:130
    +                           2427 tokio::runtime::blocking::pool::Spawner::spawn_thread::_$u7b$$u7b$closure$u7d$$u7d$::hb8d26712d1e0a87a  (in cloudfront_logs) + 41  [0x10d0865e9]  pool.rs:209
    +                             2427 tokio::runtime::handle::Handle::enter::h925b673bbbf60922  (in cloudfront_logs) + 82  [0x10d069852]  handle.rs:76
    +                               2427 tokio::runtime::context::enter::h594ce19fae3645d3  (in cloudfront_logs) + 86  [0x10d0144f6]  context.rs:72
    +                                 2427 tokio::runtime::blocking::pool::Spawner::spawn_thread::_$u7b$$u7b$closure$u7d$$u7d$::_$u7b$$u7b$closure$u7d$$u7d$::h15b91bd6f6a228cc  (in cloudfront_logs) + 55  [0x10d086567]  pool.rs:210
    +                                   2427 tokio::runtime::blocking::pool::Inner::run::h2223211aa8f5c30d  (in cloudfront_logs) + 390  [0x10d0867a6]  pool.rs:230
    +                                     2427 tokio::runtime::task::Notified$LT$S$GT$::run::h7ee3dc3c18e82cba  (in cloudfront_logs) + 29  [0x10d062c0d]  mod.rs:169
    +                                       2427 tokio::runtime::task::raw::RawTask::poll::h26d954b18474d348  (in cloudfront_logs) + 46  [0x10d06b61e]  raw.rs:66
    +                                         2427 tokio::runtime::task::raw::poll::h0fa0afc3e981bb4b  (in cloudfront_logs) + 34  [0x10ceae572]  raw.rs:104
    +                                           2427 tokio::runtime::task::harness::Harness$LT$T$C$S$GT$::poll::hf9c36b55740bbfed  (in cloudfront_logs) + 380  [0x10ced9cbc]  harness.rs:89
    +                                             2427 std::panic::catch_unwind::hbca52d9256b52aa9  (in cloudfront_logs) + 28  [0x10cec72fc]  panic.rs:394
    +                                               2427 std::panicking::try::hd71536d6d35fb12e  (in cloudfront_logs) + 135  [0x10cee18d7]  panicking.rs:325
    +                                                 2427 __rust_try  (in cloudfront_logs) + 29  [0x10cee8ebd]
    +                                                   2427 std::panicking::try::do_call::h46c34f15157635e7  (in cloudfront_logs) + 89  [0x10cee1ac9]  panicking.rs:348
    +                                                     2427 _$LT$std..panic..AssertUnwindSafe$LT$F$GT$$u20$as$u20$core..ops..function..FnOnce$LT$$LP$$RP$$GT$$GT$::call_once::h55e08800d1bb0a52  (in cloudfront_logs) + 28  [0x10cec6d0c]  panic.rs:318
    +                                                       2427 core::ops::function::FnOnce::call_once::hf27147462984b278  (in cloudfront_logs) + 32  [0x10cee2290]  function.rs:233
    +                                                         2427 tokio::runtime::task::harness::Harness$LT$T$C$S$GT$::poll::_$u7b$$u7b$closure$u7d$$u7d$::h81c651632a29d4ef  (in cloudfront_logs) + 306  [0x10ceda102]  harness.rs:107
    +                                                           2427 tokio::runtime::task::core::Core$LT$T$C$S$GT$::poll::h7b7d24a1533992f2  (in cloudfront_logs) + 54  [0x10cebac16]  core.rs:158
    +                                                             2427 tokio::loom::std::unsafe_cell::UnsafeCell$LT$T$GT$::with_mut::h377f838352fbf4a0  (in cloudfront_logs) + 82  [0x10cee0452]  unsafe_cell.rs:14
    +                                                               2427 tokio::runtime::task::core::Core$LT$T$C$S$GT$::poll::_$u7b$$u7b$closure$u7d$$u7d$::hc6bb476f4c0dbfdd  (in cloudfront_logs) + 331  [0x10cebadbb]  core.rs:173
    +                                                                 2427 _$LT$tokio..runtime..blocking..task..BlockingTask$LT$T$GT$$u20$as$u20$core..future..future..Future$GT$::poll::hf1bc8661f8dd08ef  (in cloudfront_logs) + 200  [0x10ceac368]  task.rs:38
    +                                                                   2427 _$LT$hyper..client..connect..dns..GaiResolver$u20$as$u20$tower_service..Service$LT$hyper..client..connect..dns..Name$GT$$GT$::call::_$u7b$$u7b$closure$u7d$$u7d$::h97f68211e6cfbc52  (in cloudfront_logs) + 489  [0x10cecac69]  dns.rs:122
    +                                                                     2427 _$LT$$LP$$RF$str$C$u16$RP$$u20$as$u20$std..net..addr..ToSocketAddrs$GT$::to_socket_addrs::hb8b02ee58d460452  (in cloudfront_logs) + 261  [0x10d1dea85]  addr.rs:963
    +                                                                       2427 _$LT$std..sys_common..net..LookupHost$u20$as$u20$core..convert..TryFrom$LT$$LP$$RF$str$C$u16$RP$$GT$$GT$::try_from::hf4c7dff3e0f3ab3c  (in cloudfront_logs) + 301  [0x10d1e5cdd]  net.rs:197
    +                                                                         2427 getaddrinfo  (in libsystem_info.dylib) + 61  [0x7fff63b28e7d]
    +                                                                           2427 _getaddrinfo_internal  (in libsystem_info.dylib) + 231  [0x7fff63b28f77]
    +                                                                             2427 si_addrinfo  (in libsystem_info.dylib) + 1904  [0x7fff63b29810]
    +                                                                               2427 search_addrinfo  (in libsystem_info.dylib) + 309  [0x7fff63b32d15]
    +                                                                                 2427 mdns_addrinfo  (in libsystem_info.dylib) + 1150  [0x7fff63b331ee]
    +                                                                                   2427 _mdns_search  (in libsystem_info.dylib) + 146  [0x7fff63b2d7d2]
    +                                                                                     2427 _mdns_search_ex  (in libsystem_info.dylib) + 2092  [0x7fff63b2e00c]
    +                                                                                       2427 kevent  (in libsystem_kernel.dylib) + 10  [0x7fff63b7078a]