Running the load test in a loop, after maybe a hundred iterations or so, I got a valgrind complaint: ==29504== ==29504== HEAP SUMMARY: ==29504== in use at exit: 161,360 bytes in 1,769 blocks ==29504== total heap usage: 325,601 allocs, 323,832 frees, 54,917,164 bytes allocated ==29504== ==29504== 161,296 (73 direct, 161,223 indirect) bytes in 1 blocks are definitely lost in loss record 64 of 64 ==29504== at 0x4C2B100: operator new(unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==29504== by 0x4E8A699: boost::asio::detail::thread_info_base::allocate(boost::asio::detail::thread_info_base*, unsigned long) (thread_info_base.hpp:60) ==29504== by 0x4E8A7A8: boost::asio::asio_handler_allocate(unsigned long, ...) (handler_alloc_hook.ipp:50) ==29504== by 0x4E883DE: void* boost_asio_handler_alloc_helpers::allocate const&, std::chrono::duration > const&)::{lambda(boost::system::error_code const&)#1}>(unsigned long, curl::multi::Handle::Private::Timeout::Private::async_wait_for(std::weak_ptr const&, std::chrono::duration > const&)::{lambda(boost::system::error_code const&)#1}&) (handler_alloc_helpers.hpp:37) ==29504== by 0x4E87F56: void boost::asio::detail::deadline_timer_service >::async_wait const&, std::chrono::duration > const&)::{lambda(boost::system::error_code const&)#1}>(boost::asio::detail::deadline_timer_service >::implementation_type&, curl::multi::Handle::Private::Timeout::Private::async_wait_for(std::weak_ptr const&, std::chrono::duration > const&)::{lambda(boost::system::error_code const&)#1}&) (deadline_timer_service.hpp:185) ==29504== by 0x4E87CA1: boost::asio::async_result const&, std::chrono::duration > const&)::{lambda(boost::system::error_code const&)#1}, void (boost::system::error_code)>::type>::type boost::asio::deadline_timer_service >::async_wait const&, std::chrono::duration > const&)::{lambda(boost::system::error_code const&)#1}>(boost::asio::detail::deadline_timer_service >::implementation_type&, boost::asio::handler_type&&) (deadline_timer_service.hpp:149) ==29504== by 0x4E87B93: boost::asio::async_result const&, std::chrono::duration > const&)::{lambda(boost::system::error_code const&)#1}, void (boost::system::error_code)>::type>::type boost::asio::basic_deadline_timer, boost::asio::deadline_timer_service > >::async_wait const&, std::chrono::duration > const&)::{lambda(boost::system::error_code const&)#1}>(boost::asio::handler_type&&) (basic_deadline_timer.hpp:508) ==29504== by 0x4E86A33: curl::multi::Handle::Private::Timeout::Private::async_wait_for(std::weak_ptr const&, std::chrono::duration > const&) (multi.cpp:402) ==29504== by 0x4E86730: curl::multi::Handle::Private::Timeout::async_wait_for(std::shared_ptr const&, std::chrono::duration > const&) (multi.cpp:371) ==29504== by 0x4E86C13: curl::multi::Handle::Private::timer_callback(void*, long, void*) (multi.cpp:436) ==29504== by 0x656F204: ??? (in /usr/lib/x86_64-linux-gnu/libcurl.so.4.3.0) ==29504== by 0x6570C19: curl_multi_remove_handle (in /usr/lib/x86_64-linux-gnu/libcurl.so.4.3.0) ==29504== ==29504== LEAK SUMMARY: ==29504== definitely lost: 73 bytes in 1 blocks ==29504== indirectly lost: 161,223 bytes in 1,766 blocks ==29504== possibly lost: 0 bytes in 0 blocks ==29504== still reachable: 64 bytes in 2 blocks ==29504== suppressed: 0 bytes in 0 blocks ==29504== Reachable blocks (those to which a pointer was found) are not shown. ==29504== To see them, rerun with: --leak-check=full --show-leak-kinds=all ==29504== ==29504== For counts of detected and suppressed errors, rerun with: -v ==29504== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)