[internal] Store Values and DirectoryDigests as boxed references in the workunit store.
#14749
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…ues and DirectoryDigests. [ci skip-build-wheels]
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Eric-Arellano
approved these changes
Mar 9, 2022
| pub enum UserMetadataItem { | ||
| PyValue(UserMetadataPyValue), | ||
| // NB: Always stores a ... |
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Oops, yep.
As to your other comment: the traits try to explain themselves:
// NB: Only implemented for `Value`, but is boxed to avoid a cycle between this crate and the
// `engine` crate.... as does the as_any method:
// See https://vorner.github.io/2020/08/02/fights-with-downcasting.html.
fn as_any(&self) -> &dyn Any;# Building wheels and fs_util will be skipped. Delete if not intended. [ci skip-build-wheels]
tdyas
approved these changes
Mar 9, 2022
| // is only as large as its pointers. | ||
| known_deep_size!(8 * 3; Value); | ||
| // is only as large as its pointer. | ||
| known_deep_size!(8; Value); |
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Instead of assuming the size is 8, maybe use std::mem::size_of<* cosnt ()> or some other pointer type?
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Mm, yea: good idea. I think that I wasn't sure whether it would work with the macro.
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To avoid cycles between the
workunit_storecrate and theengineandfscrates,UserMetadataItem::PyValueandArtifactOutput::Snapshotboth used indirection.But in #14723,
ArtifactOutput::Snapshotstoring ahashing::Digestwill no longer be a sufficient replacement for storing afs::DirectoryDigest, because we no longer guarantee that all (directory)Digests have actually been persisted to disk: some of them exist only in memory asDigestTries held byDirectoryDigests. And we don't want to introduce a cycle betweenfsand theworkunit_storecrate.To fix both cases, we use a
BoxedAny(technically,Arced, since we needClone), and downcast to the underlying type at the consume side.