seems lock with mutex here
(gdb) thread 4
[Switching to thread 4 (Thread 0x7f132effd700 (LWP 10132))]
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
185 ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S: No such file or directory.
(gdb) bt
#0 pthread_cond_wait@@GLIBC_2.3.2 () at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
#1 0x000000000068b38c in wait<boost::asio::detail::scoped_lock<boost::asio::detail::posix_mutex> > (lock=..., this=0x7f132effce30)
at /usr/include/boost/asio/detail/posix_event.hpp:80
#2 boost::asio::detail::task_io_service::do_run_one (this=this@entry=0x7f13200012d0, lock=..., this_thread=..., ec=...)
at /usr/include/boost/asio/detail/impl/task_io_service.ipp:395
#3 0x000000000068c621 in boost::asio::detail::task_io_service::run (this=0x7f13200012d0, ec=...) at /usr/include/boost/asio/detail/impl/task_io_service.ipp:153
#4 0x000000000068c816 in run (this=0x7f1320000e40) at /usr/include/boost/asio/impl/io_service.ipp:59
#5 operator() (this=<optimized out>) at /usr/include/boost/asio/detail/impl/resolver_service_base.ipp:32
#6 boost::asio::detail::posix_thread::func<boost::asio::detail::resolver_service_base::work_io_service_runner>::run (this=<optimized out>)
at /usr/include/boost/asio/detail/posix_thread.hpp:82
#7 0x0000000000689f42 in boost::asio::detail::boost_asio_detail_posix_thread_function (arg=0x7f1320000ee0) at /usr/include/boost/asio/detail/impl/posix_thread.ipp:64
#8 0x00007f134dc56182 in start_thread (arg=0x7f132effd700) at pthread_create.c:312
#9 0x00007f134cd5730d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:111