Most languages still handle concurrency very badly. C and C++ are clueless about concurrency. Java and C# know a little about it. Erlang and Go take it more seriously, but are intended for server-side processing. So GUI programmers don't get much help from the language.
In particular, in C and C++, there's locking, but there's no way within the language to even talk about which locks protect which data. Thus, concurrency can't be analyzed automatically. This has become a huge mess in C/C++, as more attributes ("mutable", "volatile", per-thread storage, etc.) have been bolted on to give some hints to the compiler. There's still race condition trouble between compilers and CPUs with long look-ahead and programs with heavy concurrency.
We need better hard-compiled languages that don't punt on concurrency issues. C++ could potentially have been fixed, but the C++ committee is in denial about the problem; they're still in template la-la land, adding features few need and fewer will use correctly, rather than trying to do something about reliability issues. C# is only slightly better; Microsoft Research did some work on "Polyphonic C#", but nobody seems to use that. Yes, there are lots of obscure academic languages that address concurrency. Few are used in the real world.
Ada 2005's task model is a real world, production quality approach to include concurrency in a hard-compiled language. Ada isn't exactly known for its GUI libraries (there is GtkAda), but it could be used as a foundation for an improved concurrent GUI paradigm.
This book covers the subject quite well.