User-level threads....... with threads. - Paul Turner - Google

"Multi-threaded programming is hard. Synchronous interfaces can help, but typically require lighter-weight representation of concurrency than a thread to implement efficiently. Frustratingly, this leads to a proliferation of both asynchronous and synchronous interfaces, depending on the language used.
Over the past year we've been looking at how a uniform, performant, synchronous programming model can be implemented across all of Google's core languages (C++, Java, Go, Python), while maintaining compatibility with existing code.
In this talk I will discuss new kernel interfaces which allow the use of regular threads in a co-operative fashion, with under 200ns context-switch times, and how new user-level primitives built on top of this support." http://www.linuxplumbersconf.org/2013/