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Rob Pike gave a feature-length talk on the very topic of 'concurrency vs parallelism' and although I gave up 20 minutes in (I don't think I was getting what he

by fizixer 11y ago

Rob Pike gave a feature-length talk on the very topic of 'concurrency vs parallelism' and although I gave up 20 minutes in (I don't think I was getting what he was trying to say), I assume there might be a notion behind what we call concurrency that stands independently of the parallelism/serialism divide, maybe at a different level of abstraction. I still don't understand what that notion is, that warrants using a new word other than the existing multitasking/multithreading on a single core, or parallel-processing on multiple-cores, or distributed-computing on a cluster/network. (maybe that's what it is? three different ways of achieving concurrency? but then all of it could easily be called "parallel-processing" or "multitasking") In any case, I think an article about "Introduction to Concurrency" can be considered incomplete without a discussion of comparing/contrasting it with parallelism.

toolslive 11y ago
"Concurrency is a system structuring mechanism. Parallelism is a resource." from "understanding and expressing scalable concurrency" (Turon, Phd thesis, p 29) It's the best I've found to date.
superuser2 11y ago
>I still don't understand what that notion is I was taught that the division is the goal. You use concurrency because having multiple execution contexts at "the same" time is useful, even if they are merely interleaved by the thread scheduler on the same core. E.g. an IRC server: having a thread per socket, blocking until there is some I/O to be performed on that socket, is a very workable, straightforward design. A concurrent process is concurrent for design reasons, and could not (sanely) be any other way. You use parallelism because your problem gets solved faster when worked on in parallel instead of sequence (and obviously not all problems are this way.) A parallel program running on a single core machine would not buy you any performance increase (and its design is unnecessarily convoluted.) A parallel process is parallel for performance reasons, but could be run (just proportionally slower) on a single core.
- fizixer 11y ago
  > You use concurrency because having multiple execution contexts at "the same" time is useful, even if they are merely interleaved by the thread scheduler on the same core. E.g. an IRC server: having a thread per socket, blocking until there is some I/O to be performed on that socket, is a very workable, straightforward design. So concurrency is a technical/academic/generalized term for "multitasking". And yet: - the article doesn't mention that word. - Wikipedia on concurrency doesn't mention the word. - Wikipedia on multitasking is a separate article (that does mention concurrency but doesn't clarify the relationship between the two: one being a generalization of the other). - And people go on length trying to explain the "difference" between the terms, without making a helpful connection [0] Weird, as always! [0] http://www.quora.com/What-is-the-difference-between-multitasking-and-concurrency-in-programming http://www.quora.com/What-is-the-difference-between-multitas...

by fizixer 11y ago

toolslive 11y ago

"Concurrency is a system structuring mechanism. Parallelism is a resource." from "understanding and expressing scalable concurrency" (Turon, Phd thesis, p 29) It's the best I've found to date.

superuser2 11y ago

>I still don't understand what that notion is I was taught that the division is the goal. You use concurrency because having multiple execution contexts at "the same" time is useful, even if they are merely interleaved by the thread scheduler on the same core. E.g. an IRC server: having a thread per socket, blocking until there is some I/O to be performed on that socket, is a very workable, straightforward design. A concurrent process is concurrent for design reasons, and could not (sanely) be any other way. You use parallelism because your problem gets solved faster when worked on in parallel instead of sequence (and obviously not all problems are this way.) A parallel program running on a single core machine would not buy you any performance increase (and its design is unnecessarily convoluted.) A parallel process is parallel for performance reasons, but could be run (just proportionally slower) on a single core.

fizixer 11y ago
> You use concurrency because having multiple execution contexts at "the same" time is useful, even if they are merely interleaved by the thread scheduler on the same core. E.g. an IRC server: having a thread per socket, blocking until there is some I/O to be performed on that socket, is a very workable, straightforward design. So concurrency is a technical/academic/generalized term for "multitasking". And yet: - the article doesn't mention that word. - Wikipedia on concurrency doesn't mention the word. - Wikipedia on multitasking is a separate article (that does mention concurrency but doesn't clarify the relationship between the two: one being a generalization of the other). - And people go on length trying to explain the "difference" between the terms, without making a helpful connection [0] Weird, as always! [0] http://www.quora.com/What-is-the-difference-between-multitasking-and-concurrency-in-programming http://www.quora.com/What-is-the-difference-between-multitas...