warning: catching polymorphic type ‘class boost::thread_resource_error’ by value

[martindorey]

A simple test:

martind@stormy:~/tmp/D158494$ cat polymorphic-catch.cpp 
#include "boost/threadpool/pool.hpp"

void* po = new boost::threadpool::pool;
martind@stormy:~/tmp/D158494$ 

... produces a warning when compiled with -Wall:

martind@stormy:~/tmp/D158494$ gcc -I ~/download/threadpool/ -c polymorphic-catch.cpp -Wall
In file included from /home/martind/download/threadpool/boost/threadpool/pool.hpp:27,
                 from polymorphic-catch.cpp:1:
/home/martind/download/threadpool/boost/threadpool/./detail/pool_core.hpp: In instantiation of ‘bool boost::threadpool::detail::pool_core<Task, SchedulingPolicy, SizePolicy, SizePolicyController, ShutdownPolicy>::resize(size_t) volatile [with Task = boost::function0<void>; SchedulingPolicy = boost::threadpool::fifo_scheduler; SizePolicy = boost::threadpool::static_size; SizePolicyController = boost::threadpool::resize_controller; ShutdownPolicy = boost::threadpool::wait_for_all_tasks; size_t = long unsigned int]’:
/home/martind/download/threadpool/boost/threadpool/size_policies.hpp:75:7:   required from ‘static void boost::threadpool::static_size<Pool>::init(Pool&, size_t) [with Pool = boost::threadpool::detail::pool_core<boost::function0<void>, boost::threadpool::fifo_scheduler, boost::threadpool::static_size, boost::threadpool::resize_controller, boost::threadpool::wait_for_all_tasks>; size_t = long unsigned int]’
/home/martind/download/threadpool/boost/threadpool/pool.hpp:103:29:   required from ‘boost::threadpool::thread_pool<Task, SchedulingPolicy, SizePolicy, SizePolicyController, ShutdownPolicy>::thread_pool(size_t) [with Task = boost::function0<void>; SchedulingPolicy = boost::threadpool::fifo_scheduler; SizePolicy = boost::threadpool::static_size; SizePolicyController = boost::threadpool::resize_controller; ShutdownPolicy = boost::threadpool::wait_for_all_tasks; size_t = long unsigned int]’
polymorphic-catch.cpp:3:35:   required from here
/home/martind/download/threadpool/boost/threadpool/./detail/pool_core.hpp:353:11: warning: catching polymorphic type ‘class boost::thread_resource_error’ by value [-Wcatch-value=]
           catch(thread_resource_error)
           ^~~~~
martind@stormy:~/tmp/D158494$ 

... on a gcc 8 from the Debian Buster era (2022), though it doesn't on gcc 6 from Debian Stretch (2020):

martind@stormy:~/tmp/D158494$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/8/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Debian 8.3.0-6' --with-bugurl=file:///usr/share/doc/gcc-8/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++ --prefix=/usr --with-gcc-major-version-only --program-suffix=-8 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --enable-default-pie --with-system-zlib --with-target-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 8.3.0 (Debian 8.3.0-6) 
martind@stormy:~/tmp/D158494$