std::async, std::future, std::launch, std::promisestd::asyncfuturepromise
catalogstd::asyncstd::launchfuturefuture.wait_for()future.valid, future.get(), future.wait()内部成员变量: 共享状态/数据promise获取线程返回值set_valueget_futurestd::asyncstring fetchData_fromDb0( string _info){ this_thread::sleep_for( chrono::seconds( x); return &
