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use more Rc in the part of resolver that gets cloned a lot 2 #5302

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merged 2 commits into from
Apr 6, 2018
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use more Rc in the part of resolver that gets cloned a lot 2 #5302

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736c3d7
use more Rc in the part of resolver that gets cloned a lot
Eh2406 Apr 5, 2018
04fbc5f
use make_mut for cleaner code
Eh2406 Apr 6, 2018
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13 changes: 8 additions & 5 deletions src/cargo/core/resolver/context.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -23,7 +23,7 @@ pub struct Context {
// switch to persistent hash maps if we can at some point or otherwise
// make these much cheaper to clone in general.
pub activations: Activations,
pub resolve_features: HashMap<PackageId, HashSet<InternedString>>,
pub resolve_features: HashMap<PackageId, Rc<HashSet<InternedString>>>,
pub links: HashMap<InternedString, PackageId>,

// These are two cheaply-cloneable lists (O(1) clone) which are effectively
Expand All @@ -36,6 +36,8 @@ pub struct Context {
pub warnings: RcList<String>,
}

pub type Activations = HashMap<(InternedString, SourceId), Rc<Vec<Summary>>>;

impl Context {
pub fn new() -> Context {
Context {
Expand Down Expand Up @@ -246,10 +248,13 @@ impl Context {

let set = self.resolve_features
.entry(pkgid.clone())
.or_insert_with(HashSet::new);
.or_insert_with(|| Rc::new(HashSet::new()));

let mut inner: HashSet<_> = (**set).clone();
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Could this perhaps use Rc::make_mut? That way we could have a fast path as well for when the Context hasn't been cloned?

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This is an algorithmic improvement, I think HashSet.clone() is now O(# activated * ticks) and this pr bings it to O(# activated).

I can experiment with that, here and for #5118, but I suspect it will be rare. Not only does the context need not to be cloned, but it needs not to have been cloned since last time that this package was added. Would you like me to do that expremint in this PR or in a follow up?

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I did it in this PR as it made the diff much smaller. New performance numbers on the way.

for feature in reqs.used {
set.insert(InternedString::new(feature));
inner.insert(InternedString::new(feature));
}
*set = Rc::new(inner);
}

Ok(ret)
Expand Down Expand Up @@ -405,5 +410,3 @@ impl<'r> Requirements<'r> {
}
}
}

pub type Activations = HashMap<(InternedString, SourceId), Rc<Vec<Summary>>>;