Redundant DNS lookups #81
Description
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]