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Asynchrony is not concurrency

(kristoff.it)
289 points kristoff_it | 3 comments | 18 Jul 25 19:21 UTC | HN request time: 0s | source
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threatofrain ◴[18 Jul 25 19:57 UTC] No.44609107[source]▶
IMO the author is mixed up on his definitions for concurrency.

https://lamport.azurewebsites.net/pubs/time-clocks.pdf

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tines ◴[18 Jul 25 20:16 UTC] No.44609321[source]▶
Can you explain more instead of linking a paper? I felt like the definitions were alright.

> Asynchrony: the possibility for tasks to run out of order and still be correct.

> Concurrency: the ability of a system to progress multiple tasks at a time, be it via parallelism or task switching.

> Parallelism: the ability of a system to execute more than one task simultaneously at the physical level.

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amelius ◴[18 Jul 25 21:16 UTC] No.44609915[source]▶
> Asynchrony: the possibility for tasks to run out of order and still be correct.

Can't we just call that "independent"?

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skydhash ◴[18 Jul 25 22:42 UTC] No.44610603{3}[source]▶
Not really. There may be some causal relations.
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1. amelius ◴[18 Jul 25 22:44 UTC] No.44610613{4}[source]▶
Can you give an example?
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2. skydhash ◴[19 Jul 25 01:16 UTC] No.44611648[source]▶
Locks, scheduling,... That introduce some synchronicity and so some kind of order. But it's enforced on the system and not a required mechanism.
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3. amelius ◴[19 Jul 25 08:23 UTC] No.44613615[source]▶
But if I run "ls" on a machine, and another user runs "ls" on the same machine, wouldn't you consider them independent, even though the OS uses all kinds of locks and what not under the hood?