Add condition variables and concurrent-mutexes #210
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Thanks - I agree we need something like these. But we should be careful not to simply copy the Lwt API, as we know it has problems!
I find Lwt_conditions tend to be misused. I've been wondering about splitting them into two separate concepts:
- Events (no payload).
- Variables (store a value; notify everyone if it changes; you can read the current value).
| id = Ctf.mint_id ()} | ||
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| let wait ?mutex t = | ||
| Option.iter Eio_mutex.unlock mutex; |
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Do you have examples of the mutex argument being used in Lwt code? Unless it's very common, it might be clearer to let the caller do this.
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I agree that it's not common and I took some time to understand what it's doing.
One example is in mirage-vnetif: TheLortex/mirage-vnetif@9b38e59#diff-f1be8e184de1d6478035d749a7d4e1099f4accac53644d09a68f12d6c90b0ec3R97
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Hmm, that use of a mutex looks unnecessary. Incrementing, decrementing and checking an int field are all atomic anyway with Lwt.
And remove some is_empty API from mutex
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I think the main question here is whether to make conditions safe to use across domains or not. A condition that's only used in a single domain can have a simpler API, because when However, if it's used across domains then the API needs to take a mutex because the caller needs to prevent other domains from changing the variable until it has finished using it. So maybe we need two different modules here (e.g. |
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Needs rebasing now that #223 is merged. |
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(fixed in #277) |
Hi, when porting the lwt-based Mirage networking stack to
eioI have encountered an extensive use of theLwt_condition and Lwt_mutex modules. This PR adds eio-equivalents:
ConditionandEio_mutex(Eio_mutexis prefixed because of the already existingStdlib.Mutex).Both features have straightforward implementations by using existing modules (
Semaphore/Waiters) but I think it can ease the transition fromlwttoeioto have them.This is obviously open for discussion.