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Nice resource! It explains the difference between parallelism and concurrency quite clearly. Some things can be improved though: > The difference between gree

by shmerl 8y ago

Nice resource! It explains the difference between parallelism and concurrency quite clearly. Some things can be improved though: > The difference between green and lightweight threads is that green threads aren't necessarily lightweight; an example of green threads is classic Java Virtual Machine threads, while Go goroutines are an example of lightweight threads. Saying that the difference between green and lightweight is that green aren't necessarily lightweight isn't helpful. Some explanation on what they are and when they differ would be useful.

slikts 8y ago
Thanks, and yeah, the part about lightweight threads stands to be expanded. Other missing parts are reactive vs interactive, linearizable vs serializable and push vs pull.
- eptcyka 8y ago
  The main difference between a green and a non-green thread is that the scheduling of said thread is done in userspace. Also, JVM threads are not green since the early 2000s, there's a 1:1 mapping between Java threads and actual kernel threads, and as far as I'm aware, said java threads are never migrated between different kernel threads.
  - slikts 8y ago
    You're right, I qualified it with "classic JVM threads", but a less ancient example would be better; it's just not immediately clear which green thread implementations are also relatively heavyweight like JVM green threads used to be.
    - eptcyka 8y ago
      I believe the distinction between heavyweight and green threads here is not really the correct comparison. It's more of a comparison between kernel managed (non-green) threads and userspace managed (green) threads. One could argue that Goroutines are green threads that are executed on non-green threads. It's also not infeasible to imagine a system where kernel threads are actually lightweight - single address-space unikernels come to mind.
      - slikts 8y ago
        I'll rework that section; thanks for the feedback.

by shmerl 8y ago

slikts 8y ago

Thanks, and yeah, the part about lightweight threads stands to be expanded. Other missing parts are reactive vs interactive, linearizable vs serializable and push vs pull.

eptcyka 8y ago
The main difference between a green and a non-green thread is that the scheduling of said thread is done in userspace. Also, JVM threads are not green since the early 2000s, there's a 1:1 mapping between Java threads and actual kernel threads, and as far as I'm aware, said java threads are never migrated between different kernel threads.
- slikts 8y ago
  You're right, I qualified it with "classic JVM threads", but a less ancient example would be better; it's just not immediately clear which green thread implementations are also relatively heavyweight like JVM green threads used to be.
  - eptcyka 8y ago
    I believe the distinction between heavyweight and green threads here is not really the correct comparison. It's more of a comparison between kernel managed (non-green) threads and userspace managed (green) threads. One could argue that Goroutines are green threads that are executed on non-green threads. It's also not infeasible to imagine a system where kernel threads are actually lightweight - single address-space unikernels come to mind.
    - slikts 8y ago
      I'll rework that section; thanks for the feedback.