解决配置DNS线程时core问题：

(gdb) bt
#0  0x000000000058e4db in _acquire_session (bucket=0x11c0, ip=0x2ae24f9006d0, hostname_hash=..., sm=0x2ae24f900000) at HttpSessionManager.cc:234
apache#1  0x000000000058e97b in HttpSessionManager::acquire_session (this=0xc77b60 <httpSessionManager>, cont=0x2ae24f900000, ip=0x2ae24f9006d0, hostname=0x2ae24fa80019 "127.0.0.1", ua_session=0x2ae243e60000, sm=0x2ae24f900000)
    at HttpSessionManager.cc:317
apache#2  0x000000000059d960 in HttpSM::do_http_server_open (this=0x2ae24f900000, raw=false) at HttpSM.cc:4587
apache#3  0x00000000005a5421 in HttpSM::set_next_state (this=0x2ae24f900000) at HttpSM.cc:7091
apache#4  0x00000000005a4941 in HttpSM::call_transact_and_set_next_state (this=0x2ae24f900000, f=0x0) at HttpSM.cc:6925
apache#5  0x00000000005969f3 in HttpSM::state_cache_open_write (this=0x2ae24f900000, event=1108, data=0x2ae243ee0000) at HttpSM.cc:2564
apache#6  0x0000000000597228 in HttpSM::main_handler (this=0x2ae24f900000, event=1108, data=0x2ae243ee0000) at HttpSM.cc:2683
apache#7  0x000000000050a288 in Continuation::handleEvent (this=0x2ae24f900000, event=1108, data=0x2ae243ee0000) at ../iocore/eventsystem/I_Continuation.h:146
apache#8  0x000000000057f7e6 in HttpCacheSM::state_cache_open_write (this=0x2ae24f901808, event=1108, data=0x2ae243ee0000) at HttpCacheSM.cc:180
apache#9  0x000000000050a288 in Continuation::handleEvent (this=0x2ae24f901808, event=1108, data=0x2ae243ee0000) at ../iocore/eventsystem/I_Continuation.h:146
apache#10 0x00000000006fdf28 in CacheVC::callcont (this=0x2ae243ee0000, event=1108) at P_CacheInternal.h:837
apache#11 0x00000000007058b3 in Cache::open_write (this=0x835e160, cont=0x2ae24f901808, key=0x2ae1bf337ea0, info=0x0, apin_in_cache=0, key1=0x0, type=CACHE_FRAG_TYPE_HTTP,
    hostname=0x2ae24f88000b "127.0.0.1:57890/synthetic.txt HTTP/1.0\r\n\r\n", host_len=9) at CacheWrite.cc:1823
apache#12 0x00000000006df28a in Cache::open_write (this=0x835e160, cont=0x2ae24f901808, url=0x2ae24f900750, request=0x2ae24f900738, old_info=0x0, pin_in_cache=0, type=CACHE_FRAG_TYPE_HTTP) at P_CacheInternal.h:1281
apache#13 0x00000000006db86c in CacheProcessor::open_write (this=0x11b56e0 <cacheProcessor>, cont=0x2ae24f901808, expected_size=0, url=0x2ae24f900750, cluster_cache_local=true, request=0x2ae24f900738, old_info=0x0, pin_in_cache=0,
    type=CACHE_FRAG_TYPE_HTTP) at Cache.cc:3991
apache#14 0x000000000057fc9b in HttpCacheSM::open_write (this=0x2ae24f901808, url=0x2ae24f900750, request=0x2ae24f900738, old_info=0x0, pin_in_cache=0, retry=true, allow_multiple=false) at HttpCacheSM.cc:335
apache#15 0x000000000059d2d9 in HttpSM::do_cache_prepare_action (this=0x2ae24f900000, c_sm=0x2ae24f901808, object_read_info=0x0, retry=true, allow_multiple=false) at HttpSM.cc:4490
apache#16 0x00000000005ab9da in HttpSM::do_cache_prepare_write (this=0x2ae24f900000) at HttpSM.cc:4404
apache#17 0x00000000005a57d5 in HttpSM::set_next_state (this=0x2ae24f900000) at HttpSM.cc:7179
apache#18 0x00000000005a4941 in HttpSM::call_transact_and_set_next_state (this=0x2ae24f900000, f=0x0) at HttpSM.cc:6925
apache#19 0x0000000000593e8f in HttpSM::handle_api_return (this=0x2ae24f900000) at HttpSM.cc:1611
apache#20 0x000000000059e298 in HttpSM::do_api_callout_internal (this=0x2ae24f900000) at HttpSM.cc:4783
apache#21 0x00000000005ab93c in HttpSM::do_api_callout (this=0x2ae24f900000) at HttpSM.cc:576
apache#22 0x00000000005ab97e in HttpSM::setup_cache_lookup_complete_api (this=0x2ae24f900000) at HttpSM.cc:2573
apache#23 0x0000000000596e95 in HttpSM::state_cache_open_read (this=0x2ae24f900000, event=1103, data=0xffffffffffffb050) at HttpSM.cc:2630
apache#24 0x0000000000597228 in HttpSM::main_handler (this=0x2ae24f900000, event=1103, data=0xffffffffffffb050) at HttpSM.cc:2683
apache#25 0x000000000050a288 in Continuation::handleEvent (this=0x2ae24f900000, event=1103, data=0xffffffffffffb050) at ../iocore/eventsystem/I_Continuation.h:146
apache#26 0x000000000057f61d in HttpCacheSM::state_cache_open_read (this=0x2ae24f901808, event=1103, data=0xffffffffffffb050) at HttpCacheSM.cc:145
apache#27 0x000000000050a288 in Continuation::handleEvent (this=0x2ae24f901808, event=1103, data=0xffffffffffffb050) at ../iocore/eventsystem/I_Continuation.h:146
apache#28 0x00000000006f8415 in Cache::open_read (this=0x835e160, cont=0x2ae24f901808, key=0x2ae1bf3385b0, request=0x2ae24f900738, params=0x2ae24f900108, type=CACHE_FRAG_TYPE_HTTP,
    hostname=0x2ae24f88000b "127.0.0.1:57890/synthetic.txt HTTP/1.0\r\n\r\n", host_len=9) at CacheRead.cc:162
apache#29 0x00000000006df1f9 in Cache::open_read (this=0x835e160, cont=0x2ae24f901808, url=0x2ae24f900750, request=0x2ae24f900738, params=0x2ae24f900108, type=CACHE_FRAG_TYPE_HTTP) at P_CacheInternal.h:1262
apache#30 0x00000000006db738 in CacheProcessor::open_read (this=0x11b56e0 <cacheProcessor>, cont=0x2ae24f901808, url=0x2ae24f900750, cluster_cache_local=1, request=0x2ae24f900738, params=0x2ae24f900108, pin_in_cache=0,
    type=CACHE_FRAG_TYPE_HTTP) at Cache.cc:3967
apache#31 0x000000000057f969 in HttpCacheSM::do_cache_open_read (this=0x2ae24f901808) at HttpCacheSM.cc:233
apache#32 0x000000000057fa55 in HttpCacheSM::open_read (this=0x2ae24f901808, url=0x2ae24f900750, hdr=0x2ae24f900738, params=0x2ae24f900108, pin_in_cache=0) at HttpCacheSM.cc:265
apache#33 0x000000000059ccf2 in HttpSM::do_cache_lookup_and_read (this=0x2ae24f900000) at HttpSM.cc:4349
apache#34 0x00000000005a5264 in HttpSM::set_next_state (this=0x2ae24f900000) at HttpSM.cc:7055
apache#35 0x00000000005a4941 in HttpSM::call_transact_and_set_next_state (this=0x2ae24f900000, f=0x0) at HttpSM.cc:6925
apache#36 0x0000000000593e8f in HttpSM::handle_api_return (this=0x2ae24f900000) at HttpSM.cc:1611
apache#37 0x000000000059e298 in HttpSM::do_api_callout_internal (this=0x2ae24f900000) at HttpSM.cc:4783
apache#38 0x00000000005ab93c in HttpSM::do_api_callout (this=0x2ae24f900000) at HttpSM.cc:576
apache#39 0x00000000005a49b0 in HttpSM::set_next_state (this=0x2ae24f900000) at HttpSM.cc:6959
apache#40 0x00000000005a4941 in HttpSM::call_transact_and_set_next_state (this=0x2ae24f900000, f=0x0) at HttpSM.cc:6925
apache#41 0x0000000000595ff6 in HttpSM::state_hostdb_reverse_lookup (this=0x2ae24f900000, event=500, data=0x0) at HttpSM.cc:2313
apache#42 0x0000000000597228 in HttpSM::main_handler (this=0x2ae24f900000, event=500, data=0x0) at HttpSM.cc:2683
apache#43 0x000000000050a288 in Continuation::handleEvent (this=0x2ae24f900000, event=500, data=0x0) at ../iocore/eventsystem/I_Continuation.h:146
apache#44 0x000000000067399e in HostDBContinuation::probeEvent (this=0x2ae24fb48000, event=1, e=0x2ae1bff5bf60) at HostDB.cc:2018
apache#45 0x000000000050a288 in Continuation::handleEvent (this=0x2ae24fb48000, event=1, data=0x2ae1bff5bf60) at ../iocore/eventsystem/I_Continuation.h:146
apache#46 0x000000000074758d in EThread::process_event (this=0x2ae1bf13a010, e=0x2ae1bff5bf60, calling_code=1) at UnixEThread.cc:142
apache#47 0x000000000074775e in EThread::execute (this=0x2ae1bf13a010) at UnixEThread.cc:193
apache#48 0x0000000000746820 in spawn_thread_internal (a=0x2a168d0) at Thread.cc:88
apache#49 0x00002ae1a6ab7df5 in start_thread () from /lib64/libpthread.so.0
apache#50 0x00002ae1a96d71ad in clone () from /lib64/libc.so.6

iocore/hostdb/HostDB.cc

@@ -660,7 +660,7 @@ HostDBProcessor::getby(Continuation *cont, const char *hostname, int len, sockad
   if (thread->mutex == cont->mutex) {
     thread->schedule_in(c, MUTEX_RETRY_DELAY);
   } else {
-    dnsProcessor.thread->schedule_imm(c);
+    thread->schedule_imm(c);
   }
 
   return &c->action;