A mention of Squeak in a comment on my last post reminded me of Newsqueak, an interesting little language by Rob Pike. Newsqueak has nothing to do with Squeak. Newsqueak implements Hoare’s idea of Communicating Sequential Processes.
The interesting part of Newsqueak is the channel data type. A channel is a two-way communication path. Given a variable v of type chan of int, the assignment c< - 3 sends 3 on the channel, and the expression < -c receives the next value on the channel.
Thus a channel is basically a Unix pipe, represented as a fundamental data type. It can be used for synchronization as well as communication. This should make it easier to write safe multi-threaded programs.
I've never programmed in Newsqueak, and I don't know if there are even any implementations out there outside of Plan 9. And of course it's possible to use Unix pipes to communicate between threads today, although the required kernel calls and marshalling may make them less efficient than in-process channels. Still it's interesting to think about threading using channels.
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