Unknown exception from std::promise

Question

What is wrong with the following code? When ran the program aborts with an unknown exception

#include <iostream>
#include <future>

int main() {
    auto promise = std::promise<int>{};
    auto future_one = promise.get_future();
    promise.set_value(1);

    return 0;
}

The error output is

terminate called after throwing an instance of 'std::system_error'
  what():  Unknown error -1
Aborted (core dumped)

g++ --version for me gives

g++ (Ubuntu 5.4.0-6ubuntu1~16.04.2) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

The same code works just fine on a mac

---

Note The line of code that the exception originates from is the promise.set_value(1)

Parsonage

@vu1p3n0x an empty shared state should not imply that the next get_future will throw. Also its the set_value which throws here for some reason.. – Parsonage

Put a debugger on the thing and figure out exact what is throwing that exception. There's nothing wrong with the code, and I can't reproduce the reported exception on Wandbox's GCC 5.4. – Synapse

Answer 1

In short, adding -pthread resolves your issue.

$ g++ -std=c++14 -g -pthread -o temp temp.cpp
$ ./temp

---

Details

I can reproduce the behavior on Ubuntu 16.04 with below command on compiling:

$ g++ -std=c++14 -g -o temp temp.cpp
$ ./temp
terminate called after throwing an instance of 'std::system_error'
  what():  Unknown error -1
Aborted (core dumped)

GDB dump shows:

(gdb) bt
#0  0x00007ffff74ab428 in __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:54
#1  0x00007ffff74ad02a in __GI_abort () at abort.c:89
#2  0x00007ffff7ae484d in __gnu_cxx::__verbose_terminate_handler() () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#3  0x00007ffff7ae26b6 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#4  0x00007ffff7ae2701 in std::terminate() () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#5  0x00007ffff7ae2919 in __cxa_throw () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#6  0x00007ffff7b0b7fe in std::__throw_system_error(int) () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#7  0x000000000040259b in 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*&&) (__once=...,
    __f=<unknown type in /home/mine/tempdir/temp, CU 0x0, DIE 0xe578>) at /usr/include/c++/5/mutex:746
#8  0x0000000000401e06 in std::__future_base::_State_baseV2::_M_set_result(std::function<std::unique_ptr<std::__future_base::_Result_base, std::__future_base::_Result_base::_Deleter> ()>, bool) (this=0x61ac30, __res=..., __ignore_failure=false) at /usr/include/c++/5/future:387
#9  0x0000000000402aee in std::promise<int>::set_value(int&&) (this=0x7fffffffe1c0, __r=<unknown type in /home/mine/tempdir/temp, CU 0x0, DIE 0xeb8a>) at /usr/include/c++/5/future:1075
#10 0x0000000000401759 in main () at temp.cpp:7

From the dump, we can see it's using mutex, etc. Then I realize that std::future stuff depends on thread, so it needs to link against pthread, otherwise we see this exception.

The same for std::thread

Naturopathy

wow, i should have remembered that you need the -pthread flag on many systems – Parsonage