xmake经验总结1：解决c++ future/promise抛出std::system_error的问题

Posted 2022-10-21 玄道公子

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1 背景

1.1 场景

编译器：gcc 9.4
运行系统：Ubuntu 20.04.4 LTS
xmake: v2.6.7
场景：其大致场景是使用c++的future/promise功能，类似如下示意代码：

#include <iostream>
#include <future>

using namespace std;

int main(int argc, char** argv)

    std::promise<int> p;
    p.set_value(42);
    auto f = p.get_future();
    int res = f.get();
    std::cout << "future got value: " << res << std::endl;
    return 0;

默认xmake文件如下：

add_rules("mode.debug", "mode.release")

target("explicit_stdc++")
    set_kind("binary")
    add_files("src/*.cpp")

编译运行以及执行结果如下：

gw123@DESKTOP-KJUN5HL:~/workspace/temp/xmake_test/explicit_stdc++$ xmake
checking for platform ... linux     
checking for architecture ... x86_64
[ 25%]: ccache compiling.release src/main.cpp
[ 50%]: linking.release explicit_stdc++
[100%]: build ok!
gw123@DESKTOP-KJUN5HL:~/workspace/temp/xmake_test/explicit_stdc++$ xmake run
terminate called after throwing an instance of 'std::system_error'
  what():  Unknown error -1

编译出来的执行文件的链接库如下所示：

$ ldd build/linux/x86_64/release/explicit_stdc++ 
        linux-vdso.so.1 (0x00007ffe29fbd000)
        libstdc++.so.6 => /lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f26b8abf000)
        libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f26b8aa4000)  
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f26b88b2000)
        libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f26b8763000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f26b8cb4000)

网上关于这部分的信息几乎是没有，经过一番查找，然后才开始了如下尝试，并最终找到对应的解决方案。

2 问题及现象的原因

根本原因：从c++11开始的future/promise 等于多线程编程相关的标准接口在Linux下的gcc环境下，其底层实现是需要依赖pthread相关接口的，因此需要在xmake脚本中添加相应的库依赖。

3 尝试

3.1 直接添加pthread

既然是因为c++多线程编程相关功能的底层实现在Linux下的gcc环境是依赖的pthread相关接口，而如前面所示，原始的xmake中并未显示地添加pthread库，那么直接在xmake添加pthread 库。其xmake脚本如下所示：

add_rules("mode.debug", "mode.release")

target("explicit_stdc++")
    set_kind("binary")
    add_syslinks("pthread")
    add_files("src/*.cpp")

但是从编译以及ldd的结果来看，其并未为在链接库里面新增pthread库，并且运行仍然会出错。

gw123@DESKTOP-KJUN5HL:~/workspace/temp/xmake_test/explicit_stdc++$ cat xmake.lua 
add_rules("mode.debug", "mode.release")

target("explicit_stdc++")
    set_kind("binary")
    add_syslinks("pthread")
    add_files("src/*.cpp")


gw123@DESKTOP-KJUN5HL:~/workspace/temp/xmake_test/explicit_stdc++$ xmake
[ 25%]: ccache compiling.release src/main.cpp
[ 50%]: linking.release explicit_stdc++
[100%]: build ok!

.../xmake_test/explicit_stdc++$ ldd build/linux/x86_64/release/explicit_stdc++
        linux-vdso.so.1 (0x00007fff7d3b0000)
        libstdc++.so.6 => /lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f8d9e680000)
        libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f8d9e665000)  
        libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f8d9e473000)
        libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f8d9e324000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f8d9e875000)
gw123@DESKTOP-KJUN5HL:~/workspace/temp/xmake_test/explicit_stdc++$ xmake run
terminate called after throwing an instance of 'std::system_error'
  what():  Unknown error -1

3.2 更改ld

对于这个问题，一开始笔者也是百思不得其解，折腾了半天，无奈之下，尝试将xmake的构建过程显示出来看看到底是什么情况：

gw123@DESKTOP-KJUN5HL:~/workspace/temp/xmake_test/explicit_stdc++$ xmake -vvv
[ 25%]: ccache compiling.release src/main.cpp
/usr/bin/gcc -c -m64 -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG -o build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o src/main.cpp
[ 50%]: linking.release explicit_stdc++
/usr/bin/g++ -o build/linux/x86_64/release/explicit_stdc++ build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o -m64 -s -lpthread
[100%]: build ok!

如上，所示，其是使用g++作为“ld” 进行链接的，且在链接的参数中已经有显示地添加 -lpthread。

于是想到的另一个尝试就是修改ld，使用gcc作为链接器。xmake的资料相对来说还是太少了，查找了一下，可以如下方式指定ld：

gw123@DESKTOP-KJUN5HL:~/workspace/temp/xmake_test/explicit_stdc++$ xmake f --ld=gcc
checking for platform ... linux     
checking for architecture ... x86_64
gw123@DESKTOP-KJUN5HL:~/workspace/temp/xmake_test/explicit_stdc++$ xmake -vvvv
checking for gcc ... /usr/bin/gcc
checking for the c++ compiler (cxx) ... gcc
checking for /usr/bin/gcc ... ok
checking for flags (-fPIC) ... ok
checking for flags (-fvisibility-inlines-hidden) ... ok
checking for flags (-O3) ... ok
checking for flags (-DNDEBUG) ... ok
[ 25%]: ccache compiling.release src/main.cpp
/usr/bin/gcc -c -m64 -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG -o build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o src/main.cpp
checking for flags (-MMD -MF) ... ok
checking for flags (-fdiagnostics-color=always) ... ok
checking for flags (-fPIC) ... ok
[ 50%]: linking.release explicit_stdc++
gcc -o build/linux/x86_64/release/explicit_stdc++ build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o -m64 -s -lpthread
error: /usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o: in function `std::call_once<void (std::__future_base::_State_baseV2::*)(std::function<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>*, bool*), std::__future_base::_State_baseV2*, std::function<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>*, bool*>(std::once_flag&, void (std::__future_base::_State_baseV2::*&&)(std::function<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>*, bool*), std::__future_base::_State_baseV2*&&, std::function<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>*&&, bool*&&)::lambda()#2::_FUN()':
main.cpp:(.text._ZZSt9call_onceIMNSt13__future_base13_State_baseV2EFvPSt8functionIFSt10unique_ptrINS0_12_Result_baseENS4_8_DeleterEEvEEPbEJPS1_S9_SA_EEvRSt9once_flagOT_DpOT0_ENUlvE0_4_FUNEv[_ZZSt9call_onceIMNSt13__future_base13_State_baseV2EFvPSt8functionIFSt10unique_ptrINS0_12_Result_baseENS4_8_DeleterEEvEEPbEJPS1_S9_SA_EEvRSt9once_flagOT_DpOT0_ENUlvE0_4_FUNEv]+0x7): undefined reference to `std::__once_callable'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o: in function `std::__future_base::_State_baseV2::~_State_baseV2()':
main.cpp:(.text._ZNSt13__future_base13_State_baseV2D0Ev[_ZNSt13__future_base13_State_baseV2D5Ev]+0x2a): undefined reference to `operator delete(void*, unsigned long)'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o: in function `std::_Sp_counted_ptr_inplace<std::__future_base::_State_baseV2, std::allocator<std::__future_base::_State_baseV2>, (__gnu_cxx::_Lock_policy)2>::~_Sp_counted_ptr_inplace()':     
main.cpp:(.text._ZNSt23_Sp_counted_ptr_inplaceINSt13__future_base13_State_baseV2ESaIS1_ELN9__gnu_cxx12_Lock_policyE2EED0Ev[_ZNSt23_Sp_counted_ptr_inplaceINSt13__future_base13_State_baseV2ESaIS1_ELN9__gnu_cxx12_Lock_policyE2EED5Ev]+0xa): undefined reference to `operator delete(void*, unsigned long)'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o: in function `std::__future_base::_Result<int>::~_Result()':
main.cpp:(.text._ZNSt13__future_base7_ResultIiED2Ev[_ZNSt13__future_base7_ResultIiED5Ev]+0xf): undefined reference to `std::__future_base::_Result_base::~_Result_base()'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o: in function `std::__future_base::_Result<int>::~_Result()':
main.cpp:(.text._ZNSt13__future_base7_ResultIiED0Ev[_ZNSt13__future_base7_ResultIiED5Ev]+0x13): undefined reference to `std::__future_base::_Result_base::~_Result_base()'
/usr/bin/ld: main.cpp:(.text._ZNSt13__future_base7_ResultIiED0Ev[_ZNSt13__future_base7_ResultIiED5Ev]+0x21): undefined reference to `operator delete(void*, unsigned long)'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o: in function `std::_Sp_counted_ptr_inplace<std::__future_base::_State_baseV2, std::allocator<std::__future_base::_State_baseV2>, (__gnu_cxx::_Lock_policy)2>::_M_destroy()':
main.cpp:(.text._ZNSt23_Sp_counted_ptr_inplaceINSt13__future_base13_State_baseV2ESaIS1_ELN9__gnu_cxx12_Lock_policyE2EE10_M_destroyEv[_ZNSt23_Sp_counted_ptr_inplaceINSt13__future_base13_State_baseV2ESaIS1_ELN9__gnu_cxx12_Lock_policyE2EE10_M_destroyEv]+0x5): undefined reference to `operator delete(void*)'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o: in function `std::__future_base::_State_baseV2::_M_do_set(std::function<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>*, bool*)':
main.cpp:(.text._ZNSt13__future_base13_State_baseV29_M_do_setEPSt8functionIFSt10unique_ptrINS_12_Result_baseENS3_8_DeleterEEvEEPb[_ZNSt13__future_base13_State_baseV29_M_do_setEPSt8functionIFSt10unique_ptrINS_12_Result_baseENS3_8_DeleterEEvEEPb]+0x63): undefined reference to `std::__throw_bad_function_call()'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o: in function `std::__future_base::_Result<int>::_M_destroy()':
main.cpp:(.text._ZNSt13__future_base7_ResultIiE10_M_destroyEv[_ZNSt13__future_base7_ResultIiE10_M_destroyEv]+0x26): undefined reference to `std::__future_base::_Result_base::~_Result_base()'
/usr/bin/ld: main.cpp:(.text._ZNSt13__future_base7_ResultIiE10_M_destroyEv[_ZNSt13__future_base7_ResultIiE10_M_destroyEv]+0x34): undefined reference to `operator delete(void*, unsigned long)'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o: in function `std::promise<int>::~promise()':
main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x5f): undefined reference to `std::future_category()'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x91): undefined reference to `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_replace(unsigned long, unsigned long, char const*, unsigned long)'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0xe3): undefined reference to `std::logic_error::logic_error(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0xf2): undefined reference to `operator delete(void*)'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x106): undefined reference to `operator delete(void*)'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x10d): undefined reference to `vtable for std::future_error'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x129): undefined reference to `__cxa_allocate_exception'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x137): undefined reference to `typeinfo for std::future_error'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x142): undefined reference to `__cxa_init_primary_exception'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x14d): undefined reference to `std::logic_error::logic_error(std::logic_error const&)'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x170): undefined reference to `std::__exception_ptr::exception_ptr::exception_ptr(void*)'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x18d): undefined reference to `std::__exception_ptr::exception_ptr::swap(std::__exception_ptr::exception_ptr&)'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x195): undefined reference to `std::__exception_ptr::exception_ptr::~exception_ptr()'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x19d): undefined reference to `std::__exception_ptr::exception_ptr::~exception_ptr()'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x1a5): undefined reference to `std::future_error::~future_error()'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x215): undefined reference to `std::__future_base::_Result_base::~_Result_base()'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x222): undefined reference to `operator delete(void*, unsigned long)'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x301): undefined reference to `std::__atomic_futex_unsigned_base::_M_futex_notify_all(unsigned int*)'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x324): undefined reference to `operator delete(void*)'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x338): undefined reference to `operator delete(void*)'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiED2Ev[_ZNSt7promiseIiED5Ev]+0x33d): undefined reference to `std::terminate()'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o: in function `std::promise<int>::set_value(int&&)':
main.cpp:(.text._ZNSt7promiseIiE9set_valueEOi[_ZNSt7promiseIiE9set_valueEOi]+0xe2): undefined reference to `std::__once_callable'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiE9set_valueEOi[_ZNSt7promiseIiE9set_valueEOi]+0xf6): undefined reference to `std::__once_call'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiE9set_valueEOi[_ZNSt7promiseIiE9set_valueEOi]+0x103): undefined reference to `__once_proxy'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiE9set_valueEOi[_ZNSt7promiseIiE9set_valueEOi]+0x11d): undefined reference to `std::__throw_future_error(int)'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiE9set_valueEOi[_ZNSt7promiseIiE9set_valueEOi]+0x171): undefined reference to `std::__atomic_futex_unsigned_base::_M_futex_notify_all(unsigned int*)'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiE9set_valueEOi[_ZNSt7promiseIiE9set_valueEOi]+0x17f): undefined reference to `std::__throw_system_error(int)'
/usr/bin/ld: main.cpp:(.text._ZNSt7promiseIiE9set_valueEOi[_ZNSt7promiseIiE9set_valueEOi]+0x189): undefined reference to `std::__throw_future_error(int)'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o: in function `main.cold':
main.cpp:(.text.unlikely+0x4): undefined reference to `std::__exception_ptr::exception_ptr::~exception_ptr()'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o: in function `main':
main.cpp:(.text.startup+0x31): undefined reference to `operator new(unsigned long)'
/usr/bin/ld: main.cpp:(.text.startup+0x86): undefined reference to `operator new(unsigned long)'
/usr/bin/ld: main.cpp:(.text.startup+0x9b): undefined reference to `std::__future_base::_Result_base::_Result_base()'
/usr/bin/ld: main.cpp:(.text.startup+0x142): undefined reference to `std::__atomic_futex_unsigned_base::_M_futex_wait_until(unsigned int*, unsigned int, bool, std::chrono::duration<long, std::ratio<1l, 1l> >, std::chrono::duration<long, std::ratio<1l, 1000000000l> >)'/usr/bin/ld: main.cpp:(.text.startup+0x16e): undefined reference to `std::__exception_ptr::operator==(std::__exception_ptr::exception_ptr const&, std::__exception_ptr::exception_ptr const&)'
/usr/bin/ld: main.cpp:(.text.startup+0x178): undefined reference to `std::__exception_ptr::exception_ptr::~exception_ptr()'
/usr/bin/ld: main.cpp:(.text.startup+0x1b6): undefined reference to `std::cout'
/usr/bin/ld: main.cpp:(.text.startup+0x1bb): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::__ostream_insert<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*, long)'
/usr/bin/ld: main.cpp:(.text.startup+0x1c5): undefined reference to `std::cout'
/usr/bin/ld: main.cpp:(.text.startup+0x1ca): undefined reference to `std::ostream::operator<<(int)'
/usr/bin/ld: main.cpp:(.text.startup+0x1d2): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::endl<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&)'
/usr/bin/ld: main.cpp:(.text.startup+0x253): undefined reference to `std::__throw_future_error(int)'
/usr/bin/ld: main.cpp:(.text.startup+0x262): undefined reference to `std::__throw_future_error(int)'
/usr/bin/ld: main.cpp:(.text.startup+0x26d): undefined reference to `std::__exception_ptr::exception_ptr::exception_ptr(std::__exception_ptr::exception_ptr const&)'
/usr/bin/ld: main.cpp:(.text.startup+0x275): undefined reference to `std::rethrow_exception(std::__exception_ptr::exception_ptr)'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o: in function `_GLOBAL__sub_I_main':
main.cpp:(.text.startup+0x2d0): undefined reference to `std::ios_base::Init::Init()'
/usr/bin/ld: main.cpp:(.text.startup+0x2d7): undefined reference to `std::ios_base::Init::~Init()'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o:(.data.rel.ro._ZTISt11_Mutex_baseILN9__gnu_cxx12_Lock_policyE2EE[_ZTISt11_Mutex_baseILN9__gnu_cxx12_Lock_policyE2EE]+0x0): undefined reference to `vtable for __cxxabiv1::__class_type_info'   
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o:(.data.rel.ro._ZTISt16_Sp_counted_baseILN9__gnu_cxx12_Lock_policyE2EE[_ZTISt16_Sp_counted_baseILN9__gnu_cxx12_Lock_policyE2EE]+0x0): undefined reference to `vtable for __cxxabiv1::__si_class_type_info'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o:(.data.rel.ro._ZTINSt13__future_base13_State_baseV2E[_ZTINSt13__future_base13_State_baseV2E]+0x0): undefined reference to `vtable for __cxxabiv1::__class_type_info'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o:(.data.rel.ro._ZTINSt13__future_base7_ResultIiEE[_ZTINSt13__future_base7_ResultIiEE]+0x0): undefined reference to `vtable for __cxxabiv1::__si_class_type_info'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o:(.data.rel.ro._ZTINSt13__future_base7_ResultIiEE[_ZTINSt13__future_base7_ResultIiEE]+0x10): undefined reference to `typeinfo for std::__future_base::_Result_base'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o:(.data.rel.ro._ZTINSt13__future_base13_State_baseV27_SetterIiOiEE[_ZTINSt13__future_base13_State_baseV27_SetterIiOiEE]+0x0): undefined reference to `vtable for __cxxabiv1::__class_type_info' 
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o:(.data.rel.ro._ZTISt23_Sp_counted_ptr_inplaceINSt13__future_base13_State_baseV2ESaIS1_ELN9__gnu_cxx12_Lock_policyE2EE[_ZTISt23_Sp_counted_ptr_inplaceINSt13__future_base13_State_baseV2ESaIS1_ELN9__gnu_cxx12_Lock_policyE2EE]+0x0): undefined reference to `vtable for __cxxabiv1::__si_class_type_info'
/usr/bin/ld: build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o:(.data.rel.local.DW.ref.__gxx_personality_v0[DW.ref.__gxx_personality_v0]+0x0): undefined reference to `__gxx_personality_v0'
collect2: error: ld returned 1 exit status

其结果如上，其根本原因是，使用gcc作为链接器，它不会默认链接c++的标准库，因此需要显示在xmake中添加，如下所示：

add_rules("mode.debug", "mode.release")

target("explicit_stdc++")
    set_kind("binary")
    add_syslinks("stdc++", "pthread")
    add_files("src/*.cpp")

其编译和运行结果，如下所示：

gw123@DESKTOP-KJUN5HL:~/workspace/temp/xmake_test/explicit_stdc++$ xmake -vvvv
checking for gcc ... /usr/bin/gcc
checking for dmd ... no
checking for ldc2 ... no
checking for gdc ... no
checking for zig ... no
checking for zig ... no
checking for gcc ... /usr/bin/gcc
checking for the c++ compiler (cxx) ... gcc
checking for /usr/bin/gcc ... ok
checking for flags (-fPIC) ... ok
checking for flags (-fvisibility-inlines-hidden) ... ok
checking for flags (-O3) ... ok
checking for flags (-DNDEBUG) ... ok
[ 25%]: ccache compiling.release src/main.cpp
/usr/bin/gcc -c -m64 -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG -o build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o src/main.cpp
checking for flags (-MMD -MF) ... ok
checking for flags (-fdiagnostics-color=always) ... ok
checking for flags (-fPIC) ... ok
[ 50%]: linking.release explicit_stdc++
gcc -o build/linux/x86_64/release/explicit_stdc++ build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o -m64 -s -lstdc++ -lpthread
[100%]: build ok!
gw123@DESKTOP-KJUN5HL:~/workspace/temp/xmake_test/explicit_stdc++$ xmake run
future got value: 42

如上所示，已经解决了此问题，可以程序可以正常运行了。

Note: 此种解决方案有两个问题：

需要显示地更改ld，构建过程多了xmake f xxx 这样的配置过程
不同操作系统或者运行环境，使用的c++标准库可能会有不同，因此添加的“stdc++”标准可可能需要根据情况进行灵活变更

3.3 只需显示添加sdc++库

虽然根据3.2节可以解决问题，但感觉还是有些复杂。于是乎做了一番尝试，发现其实只需要显示地添加stdc++标准库，即使使用默认的g++作为链接器，也可以正常的编译和运行。如下所示：

gw123@DESKTOP-KJUN5HL:~/workspace/temp/xmake_test/explicit_stdc++$ xmake -vvvv
checking for platform ... linux     
checking for architecture ... x86_64
checking for gcc ... /usr/bin/gcc
checking for dmd ... no
checking for ldc2 ... no
checking for gdc ... no
checking for zig ... no
checking for zig ... no
checking for gcc ... /usr/bin/gcc
checking for the c++ compiler (cxx) ... gcc
checking for /usr/bin/gcc ... ok
checking for flags (-fPIC) ... ok
checking for flags (-fvisibility-inlines-hidden) ... ok
checking for flags (-O3) ... ok
checking for flags (-DNDEBUG) ... ok
[ 25%]: ccache compiling.release src/main.cpp
/usr/bin/gcc -c -m64 -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG -o build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o src/main.cpp
checking for flags (-MMD -MF) ... ok
checking for flags (-fdiagnostics-color=always) ... ok
checking for g++ ... /usr/bin/g++
checking for the linker (ld) ... g++
checking for /usr/bin/g++ ... ok    
checking for flags (-fPIC) ... ok
[ 50%]: linking.release explicit_stdc++
/usr/bin/g++ -o build/linux/x86_64/release/explicit_stdc++ build/.objs/explicit_stdc++/linux/x86_64/release/src/main.cpp.o -m64 -s -lstdc++ -lpthread
[100%]: build ok!
gw123@DESKTOP-KJUN5HL:~/workspace/temp/xmake_test/explicit_stdc++$ xmake run
future got value: 42

至此，问题解决，笔者最终也是选择的最后这种方案，只需显示地添加stdc++库和pthread库即可。至于这其中的根本原因，笔者目前还不胜了解[捂脸]。有知道其根本原因的大牛也希望能不吝赐教[抱拳]

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