heap-use-after-free when shutting down envoy.

[fengli79]

caught SIGTERM
main dispatch loop exited
exiting
WARNING: ThreadSanitizer: heap-use-after-free (pid=806410)
Read of size 8 at 0x7b54000006c0 by main thread:
 #0 event_del third_party/libevent/src/event.c:2288:2
 #1 Event::ImplBase::~ImplBase() third_party/envoy/src/source/common/event/event_impl_base.cc:9:3
 #2 ~FileEventImpl third_party/envoy/src/source/common/event/file_event_impl.h:13:7
 #3 Event::FileEventImpl::~FileEventImpl() third_party/envoy/src/source/common/event/file_event_impl.h:13
 #4 operator() unique_ptr.h:76:2
 #5 ~unique_ptr unique_ptr.h:236
 #6 ~HotRestartImpl third_party/envoy/src/source/exe/hot_restart.h:79
 #7 Server::HotRestartImpl::~HotRestartImpl() third_party/envoy/src/source/exe/hot_restart.h:79
 #8 operator() unique_ptr.h:76:2
 #9 ~unique_ptr unique_ptr.h:236
 #10 main third_party/envoy/src/source/exe/main.cc:57
Previous write of size 8 at 0x7b54000006c0 by main thread:
 #0 free third_party/llvm/llvm/projects/compiler-rt/lib/tsan/rtl/tsan_interceptors.cc:629:3
 #1 event_mm_free_ third_party/libevent/src/event.c:2826:3
 #2 event_base_free third_party/libevent/src/event.c:842
 #3 ~unique_ptr unique_ptr.h:236:4
 #4 Event::DispatcherImpl::~DispatcherImpl() third_party/envoy/src/source/common/event/dispatcher_impl.cc:25
 #5 Event::DispatcherImpl::~DispatcherImpl() third_party/envoy/src/source/common/event/dispatcher_impl.cc:25:35
 #6 operator() unique_ptr.h:76:2
 #7 ~unique_ptr unique_ptr.h:236
 #8 Server::ConnectionHandlerImpl::~ConnectionHandlerImpl() third_party/envoy/src/source/server/connection_handler_impl.cc:19 
 #9 Server::InstanceImpl::~InstanceImpl() third_party/envoy/src/source/server/server.cc:356:32
 #10 main third_party/envoy/src/source/exe/main.cc:57:1
SUMMARY: ThreadSanitizer: heap-use-after-free third_party/libevent/src/event.c:2288:2 in event_del

I get a tsan heap use after free error. Which happens when shutting down envoy with sigterm.

[mattklein123]

@fengli79 per offline discussion are you going to post PR to fix? Otherwise I can do it.

[fengli79]

Yes, I'm going to submit a PR to fix this.

[mattklein123]

fixed by #758