Go-Flavored Concurrency in C

2 months ago (antonz.org)

Just a small "ackchyually": Go is basically a modern Limbo which is itself based on Alef and there was an official "Alef for C" thing in Plan 9 in libthread (https://9p.io/magic/man2html/2/thread)

EDIT: looks like it was ported on UNIX as part of Plan9Port (https://github.com/9fans/plan9port/blob/master/src/libthread...)

  • Russ Cox created libtask, a similar library that runs on multiple UNIXes (UNIXEN?). Based on the COPYRIGHT file, it may be based on libthread.

    https://swtch.com/libtask/

    It’s a great little library. Very easy to read and understand.

  • As I recall, Bell Labs actually abandoned Alef on Plan 9 because the concurrency primitives they wanted were doable in C so they just went with that.

    • Nope, they abandoned it because the language design was unsound, and in retrospective a GC was a critical missing piece.

      "Alef appeared in the first and second editions of Plan 9, but was abandoned during development of the third edition.[1][2] Rob Pike later explained Alef's demise by pointing to its lack of automatic memory management, despite Pike's and other people's urging Winterbottom to add garbage collection to the language;[3] also, in a February 2000 slideshow, Pike noted: "…although Alef was a fruitful language, it proved too difficult to maintain a variant language across multiple architectures, so we took what we learned from it and built the thread library for C."

      https://en.wikipedia.org/wiki/Alef_(programming_language)

      "Problem: with C's memory model in a concurrent world, hard to know when to free items.

      All the other languages in this talk are garbage-collected, which is essential to easy concurrent programming"

      http://go-lang.cat-v.org/talks/slides/emerging-languages-cam..., slide 19

But select statements are the most important part, and second to that is the fact that goroutines are low cost user space threads

  • Yes exactly. The author’s design decisions only make sense if this is supposed to be a toy language. On using pthreads rather than fibers:

    > I decided not to use one. I wanted something dead simple — an approach I could explain in a paragraph, using tools every C programmer already knows. The trade-off is that you lose some performance with fine-grained blocking, but in many real-world situations, pthreads work fine if you use a worker pool.

    Sure. You can take a large production Go app and measure how many user space threads are launched; it’s decidedly a lot more than the typical number of threads if you were using pthreads.

    And the author didn’t really justify why select isn’t implemented other than implementation difficulty.

    • I've been using Go regularly since 2012. Worker pools are completely valid and idiomatic in Go. Not sure how you read that quote and concluded "toy".

I was expecting proper green threads (it's not like it's impossible in C, there's several C libraries for doing it).