Thread safety.

[SmileGobo]

The implementation has no mutexes. When calling resolve or reject, you must ensure that either then|fail will be called before or after.
Or was a different usage strategy intended?
I have synchronization failure by assertion

cpp-promise/promise.hpp

Line 600 in c85dd10

assert((mSharedObj->mResolved == kNotResolved));

promise::Promise<int> loadDataFromSomeThread() {
    
     promise::Promise<int> pms;
     std::thread t{[pms](){
           //do some ....
     }};
     t.deatach();
     return pms;
}
int main() {
     std::promise<int> pms;     //it's waitable barier 
     auto f = pms.get_future();
     
     loadDataFromSomeThread()
         .then([&pms](int val){
             pms.set_value(val);
         })
        .fail([&pms](const promise::Error& err) { // There is a synchronization failure at this point
              pms.set_exception(new std::runtimer_error{err.msg()})
         )};
     std::cout << f.get() << std::endl;
     return 0;
}

[alxvasilev]

This promise implementation is not intended for threading - the idea is to use it in a single-threaded cooperative multitasking environment, similar to what javascript is. For inter-thread synchronization and communication, the standard C++ library already has facilities like std::promise and std::future.