Core features from <future>

[nmcclatchey]

Implements core features of the C++11 <future> header. Specifically, this pull request adds support for

• future
• shared_future
• promise
• async

Some work yet remains before the library can be considered final. Specifically,

• packaged_task is not yet implemented.
  • It can be implemented as a wrapper around std::function and a promise, or the classes internal to mingw.future.h can be employed.
• The implementation of promise<T>::set_value_at_thread_exit currently uses a second "helper thread" that detects when the original thread exits. This is, of course, inefficient, but I do not yet know another way to ensure that the value is set only after all thread_local objects are destroyed. This approach should be replaced later, if doing so is possible.

Though unrelated, the pull request also changes certain protected members of thread to be private and replaces a standard-violating macro. Names with an underscore followed by a capital letter are reserved by the standard; the macro's purpose can be accomplished safely by using a static constexpr variable at class scope instead.

[Jamaika1]

Hi team I used your mingw-std-threads-6bd14b1ba5946b18de2f2239fca2b108152cd503.zip attachment. I know that there are still tests. Unfortunately, I have a problem with libheif.

mingw.future.h: In instantiation of 'static void _mingw_stdthread::detail::StorageHelper::store_deferred(mingw_stdthread::detail::FutureState, Func&&, Args&& ...) [with Func = heif::Error (heif::HeifContext::&)(unsigned int, std::shared_ptr, int, int) const; Args = {const heif::HeifContext*&, unsigned int&, std::sharedptr&, int&, int&}; Ret = heif::Error]':

_mingw.future.h:947:19: required from 'static void mingw_stdthread::detail::StorageHelper::store(mingw_stdthread::detail::FutureState, Func&&, Args&& ...) [with Func = heif::Error (heif::HeifContext::&)(unsigned int, std::shared_ptr, int, int) const; Args = {const heif::HeifContext*&, unsigned int&, std::sharedptr&, int&, int&}; Ret = heif::Error]'

_mingw.future.h:1066:24: required from 'std::future<typename std::__invoke_result<typename std::decay<_Tp>::type, typename std::decay<_Args>::type ...>::type> std::async(std::launch, _Fn&&, _Args&& ...) [with _Fn = heif::Error (heif::HeifContext::)(unsigned int, std::shared_ptr, int, int) const; _Args = {const heif::HeifContext, unsigned int&, std::shared_ptr&, int&, int&}; typename std::__invoke_result<typename std::decay<_Tp>::type, typename std::decay<_Args>::type ...>::type = heif::Error]'_

_heifcontext.cc:1185:77: required from here

_mingw.future.h:938:52: error: must use '.' or '->' to call pointer-to-member function in 'std::forward<heif::Error (heif::HeifContext::&)(unsigned int, std::shared_ptr, int, int) const>(( & func)) (...)', e.g. '(... -> std::forward<heif::Error (heif::HeifContext::&)(unsigned int, std::sharedptr, int, int) const>((* & func))) (...)'

938 | state_ptr->set_value(std::forward(func)(std::forward(args)...));

[nmcclatchey]

Good catch. I'll replace the function call with invoke.

[nmcclatchey]

That particular problem should be fixed. If you find any others, please let me know ASAP.

[Jamaika1]

Thanks