Asyncify the Tree Building #975
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benbierens
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Image from this branch passes upload/download dist-tests. This means that the cause of failing downloads cannot be explained by long-blocking operations. |
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OK, this looks fine, with the caveats that:
- it's hackish, and IMHO we should revert it once we can run those easily on separate threads, which would be the "proper" solution;
- I am not so sure about the new/init API. It doesn't seem to comply with the expected semantics;
- we're doing some behavior-changing transformations by catching the exceptions and returning results.
Would be wise to get another pair of eyes on this as we've discussed earlier today, I'm nevertheless approving it.
| let | ||
| mhash = ? mcodec.mhash() |
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What the heck did this = ? even do?
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🟡 OK this raises an exception, so this change is actually modifying behavior. I suppose this is OK if it doesn't break expectations at callers, but we could simply preserve this behavior and propagate the exception using a Chronos raises clause. I see you've done this change in several places, and I'm assuming you did the due diligence to ensure this doesn't cause surprises, so I won't block your PR for this.
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we could simply preserve this behavior and propagate the exception using a Chronos raises clause
That would actually change the behaviour. = ? will either assign a value to mhash or it will return a Result with an error to the closure. By raising an exception, and specifying that exception type in {.async: (raises: [...]).}, we're not returning a Result, but raising an exception.
Imo, the proposed change here does not alter the behaviour.
| @@ -305,6 +304,29 @@ proc buildManifest*[T, H](self: SlotsBuilder[T, H]): Future[?!Manifest] {.async. | |||
| self.cellSize, | |||
| self.strategy.strategyType) | |||
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| proc init*[T, H](self: SlotsBuilder[T, H]): Future[?!void] {.async.} = | |||
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🟡 Hm... I think the fact that you need to call new and then init is not expected. According to the Status style guide and to some of our own code (e.g. here), init is supposed to return a constructed object (and not void), so it'd actually replace new in this case?
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Agree that an init call can be confusing when not used for construction. In general, Codex follows the convention of using init for constructing object types and new for constructing ref types, as per @dryajov's comment: https://discord.com/channels/895609329053474826/895622391349272637/1086322836001534072
Maybe an easy fix is to call this initialise instead?
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A lot of this seems like it was replacing let x = ? someResultFunc()... with without x =? someResultFunc(), which doesn't seem necessary to me. In other words, it feels like we should make the switch to async without changing any other semantics if possible. It's easy to get into trouble modifying lines "while we're here" as there can be unintended consequences, especially in nim and especially with this many changes in a PR.
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I wouldn't have changed them if I didn't have to. = ? doesn't compile in async procs.
| @@ -91,6 +91,8 @@ asyncchecksuite "Test Node - Host contracts": | |||
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| protected = (await erasure.encode(manifest, 3, 2)).tryGet() | |||
| builder = Poseidon2Builder.new(localStore, protected).tryGet() | |||
| (await builder.init()).tryGet() | |||
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Hm... this looks quite weird (doing a get on a void) but OK, I don't have better ideas. :-)
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Yeah, it's odd... but it's a way to force an exception in case there is no value.
Another way (not sure if it's "better"):
if (await builder.init()).isErr: fail()But this doesn't give much output if it does fail, so an even more explicit way is:
if error =? (await builder.init()).errorOption:
echo error.msg
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(await ...).tryGet() calls are all over the testing code. It fails the test when the result is an error. How would you like to see this changed?
| @@ -145,16 +145,18 @@ func compress*( | |||
| mhash.coder(@x & @y & @[ key.byte ], digest) | |||
| success digest | |||
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| func init*( | |||
| proc init*( | |||
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I think we might need to avoid making this init async so we can avoid using waitFor later on... instead this is a good pattern to follow:
https://github.com/codex-storage/nim-ethers/blob/80b2ead97ce32cca74cef4a4501ab97106cb578b/ethers/providers/jsonrpc.nim#L50-L86
Then later, we can use CodexTree.init synchronously, and when needed, we can let layers = await tree.layers
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I like this pattern. If I applied it, SlotBuilder verifyTree and verifyRoot funcs would have to become async procs to await for the internal field. This would propagate the asycing through the codebase further. Is this desirable? Or is there a way around this?
| without mhash =? leaves[0].mhash.mapFailure, error: | ||
| return failure error | ||
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| var hashes = newSeq[seq[byte]]() | ||
| for leaf in leaves: | ||
| without hash =? leaf.mhash.mapFailure, error: | ||
| return failure error | ||
| hashes.add(hash.digestBytes) |
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Did this really need a rewrite? In other words, was there a compilation issue that forced this re-write?
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I couldn't figure out a cleaner way to unroll the results. If you've got one, I'm eager to learn.
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I'll remove my requested changes as I realise the call sites using waitFor are in the tests only. However, that is not to say that this pattern of using async init won't bite us later on. I just don't want to stand in the way of progress.
My overall comment for these changes is that because we are making so many changes here and it feels like we're trying to rush this in, we really should limit the scope of changes by changing as little as possible. If i understood correctly, the main idea of this PR was the make some things asynchronous. However, we've also replaced let x = ? someResultFunc()... with without x =? someResultFunc() in quite a few places. This is one of those things that seems innocuous, but can also bite us later on (especially in nim).
I am also not a big fan of "let's do this for now and revert later" kind of changes, mostly because there may be patches affecting this code in the meantime which are hard to merge, and also sometimes reversion are forgotten or partially done.
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Ok, so I didn't approve these changes. I merely wanted to remove my changes requested 🤦 |
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All right. Let's put a break on this one. Here's why: The change I made is to make the tree-building async by adding a small async-sleep in the loop so the process can be interrupted for, for example, the handling of network traffic. That's it. All other changes I made are required downstream changes to make stuff compile and work again. Yes, there are a lot of those. There's not much we can do about that unless we are considering restructuring a lot more code, which is the opposite of making small changes. The new |
Investigation into node stability shows that tree-building is blocking the main execution loop for long periods of time in some use-cases. This PR breaks up the execution time by asyncifying the tree-building call chain.