feat: concurrent metadata fetching

Cargo.toml

@@ -18,9 +18,12 @@ tracing = "0.1.37"
 elsa = "1.9.0"
 bitvec = "1.0.1"
 serde = { version = "1.0", features = ["derive"], optional = true }
+futures = { version = "0.3.30", default-features = false, features = ["alloc"] }
+tokio = { version = "1.35.1", features = ["rt", "sync"] }
 
 [dev-dependencies]
 insta = "1.31.0"
 indexmap = "2.0.0"
 proptest = "1.2.0"
 tracing-test = { version = "0.2.4", features = ["no-env-filter"] }
+tokio = { version = "1.35.1", features = ["time"] }

src/lib.rs

@@ -30,6 +30,7 @@ use std::{
     any::Any,
     fmt::{Debug, Display},
     hash::Hash,
+    rc::Rc,
 };
 
 /// The solver is based around the fact that for for every package name we are trying to find a
@@ -61,21 +62,37 @@ pub trait VersionSet: Debug + Display + Clone + Eq + Hash {
 /// packages that are available in the system.
 pub trait DependencyProvider<VS: VersionSet, N: PackageName = String>: Sized {
     /// Returns the [`Pool`] that is used to allocate the Ids returned from this instance
-    fn pool(&self) -> &Pool<VS, N>;
+    fn pool(&self) -> Rc<Pool<VS, N>>;
 
     /// Sort the specified solvables based on which solvable to try first. The solver will
     /// iteratively try to select the highest version. If a conflict is found with the highest
     /// version the next version is tried. This continues until a solution is found.
     fn sort_candidates(&self, solver: &SolverCache<VS, N, Self>, solvables: &mut [SolvableId]);
 
-    /// Returns a list of solvables that should be considered when a package with the given name is
+    /// Obtains a list of solvables that should be considered when a package with the given name is
     /// requested.
     ///
-    /// Returns `None` if no such package exist.
-    fn get_candidates(&self, name: NameId) -> Option<Candidates>;
+    /// # Async
+    ///
+    /// The returned future will be awaited by a tokio runtime blocking the main thread. You are
+    /// free to use other runtimes in your implementation, as long as the runtime-specific code runs
+    /// in threads controlled by that runtime (and _not_ in the main thread). For instance, you can
+    /// use `async_std::task::spawn` to spawn a new task, use `async_std::io` inside the task to
+    /// retrieve necessary information from the network, and `await` the returned task handle.
+    #[allow(async_fn_in_trait)]
+    async fn get_candidates(&self, name: NameId) -> Option<Candidates>;
 
     /// Returns the dependencies for the specified solvable.
-    fn get_dependencies(&self, solvable: SolvableId) -> Dependencies;
+    ///
+    /// # Async
+    ///
+    /// The returned future will be awaited by a tokio runtime blocking the main thread. You are
+    /// free to use other runtimes in your implementation, as long as the runtime-specific code runs
+    /// in threads controlled by that runtime (and _not_ in the main thread). For instance, you can
+    /// use `async_std::task::spawn` to spawn a new task, use `async_std::io` inside the task to
+    /// retrieve necessary information from the network, and `await` the returned task handle.
+    #[allow(async_fn_in_trait)]
+    async fn get_dependencies(&self, solvable: SolvableId) -> Dependencies;
 
     /// Whether the solver should stop the dependency resolution algorithm.
     ///

src/problem.rs

@@ -4,7 +4,6 @@ use std::collections::{HashMap, HashSet};
 use std::fmt;
 use std::fmt::{Display, Formatter};
 use std::hash::Hash;
-
 use std::rc::Rc;
 
 use itertools::Itertools;
@@ -52,7 +51,7 @@ impl Problem {
         let unresolved_node = graph.add_node(ProblemNode::UnresolvedDependency);
 
         for clause_id in &self.clauses {
-            let clause = &solver.clauses[*clause_id].kind;
+            let clause = &solver.clauses.borrow()[*clause_id].kind;
             match clause {
                 Clause::InstallRoot => (),
                 Clause::Excluded(solvable, reason) => {
@@ -65,7 +64,7 @@ impl Problem {
                 &Clause::Requires(package_id, version_set_id) => {
                     let package_node = Self::add_node(&mut graph, &mut nodes, package_id);
 
-                    let candidates = solver.cache.get_or_cache_sorted_candidates(version_set_id).unwrap_or_else(|_| {
+                    let candidates = solver.async_runtime.block_on(solver.cache.get_or_cache_sorted_candidates(version_set_id)).unwrap_or_else(|_| {
                         unreachable!("The version set was used in the solver, so it must have been cached. Therefore cancellation is impossible here and we cannot get an `Err(...)`")
                     });
                     if candidates.is_empty() {
@@ -162,10 +161,11 @@ impl Problem {
     >(
         &self,
         solver: &'a Solver<VS, N, D>,
+        pool: Rc<Pool<VS, N>>,
         merged_solvable_display: &'a M,
     ) -> DisplayUnsat<'a, VS, N, M> {
         let graph = self.graph(solver);
-        DisplayUnsat::new(graph, solver.pool(), merged_solvable_display)
+        DisplayUnsat::new(graph, pool, merged_solvable_display)
     }
 }
 
@@ -512,7 +512,7 @@ pub struct DisplayUnsat<'pool, VS: VersionSet, N: PackageName + Display, M: Solv
     merged_candidates: HashMap<SolvableId, Rc<MergedProblemNode>>,
     installable_set: HashSet<NodeIndex>,
     missing_set: HashSet<NodeIndex>,
-    pool: &'pool Pool<VS, N>,
+    pool: Rc<Pool<VS, N>>,
     merged_solvable_display: &'pool M,
 }
 
@@ -521,10 +521,10 @@ impl<'pool, VS: VersionSet, N: PackageName + Display, M: SolvableDisplay<VS, N>>
 {
     pub(crate) fn new(
         graph: ProblemGraph,
-        pool: &'pool Pool<VS, N>,
+        pool: Rc<Pool<VS, N>>,
         merged_solvable_display: &'pool M,
     ) -> Self {
-        let merged_candidates = graph.simplify(pool);
+        let merged_candidates = graph.simplify(&pool);
         let installable_set = graph.get_installable_set();
         let missing_set = graph.get_missing_set();
 
@@ -666,10 +666,10 @@ impl<'pool, VS: VersionSet, N: PackageName + Display, M: SolvableDisplay<VS, N>>
                     let version = if let Some(merged) = self.merged_candidates.get(&solvable_id) {
                         reported.extend(merged.ids.iter().cloned());
                         self.merged_solvable_display
-                            .display_candidates(self.pool, &merged.ids)
+                            .display_candidates(&self.pool, &merged.ids)
                     } else {
                         self.merged_solvable_display
-                            .display_candidates(self.pool, &[solvable_id])
+                            .display_candidates(&self.pool, &[solvable_id])
                     };
 
                     let excluded = graph
@@ -790,9 +790,9 @@ impl<VS: VersionSet, N: PackageName + Display, M: SolvableDisplay<VS, N>> fmt::D
                         writeln!(
                             f,
                             "{indent}{} {} is locked, but another version is required as reported above",
-                            locked.name.display(self.pool),
+                            locked.name.display(&self.pool),
                             self.merged_solvable_display
-                                .display_candidates(self.pool, &[solvable_id])
+                                .display_candidates(&self.pool, &[solvable_id])
                         )?;
                     }
                     ConflictCause::Excluded(_, _) => continue,

src/solver/cache.rs

@@ -13,6 +13,7 @@ use elsa::FrozenMap;
 use std::any::Any;
 use std::cell::RefCell;
 use std::marker::PhantomData;
+use std::rc::Rc;
 
 /// Keeps a cache of previously computed and/or requested information about solvables and version
 /// sets.
@@ -65,7 +66,7 @@ impl<VS: VersionSet, N: PackageName, D: DependencyProvider<VS, N>> SolverCache<V
     }
 
     /// Returns a reference to the pool used by the solver
-    pub fn pool(&self) -> &Pool<VS, N> {
+    pub fn pool(&self) -> Rc<Pool<VS, N>> {
         self.provider.pool()
     }
 
@@ -74,7 +75,7 @@ impl<VS: VersionSet, N: PackageName, D: DependencyProvider<VS, N>> SolverCache<V
     ///
     /// If the provider has requested the solving process to be cancelled, the cancellation value
     /// will be returned as an `Err(...)`.
-    pub fn get_or_cache_candidates(
+    pub async fn get_or_cache_candidates(
         &self,
         package_name: NameId,
     ) -> Result<&Candidates, Box<dyn Any>> {
@@ -93,6 +94,7 @@ impl<VS: VersionSet, N: PackageName, D: DependencyProvider<VS, N>> SolverCache<V
                 let candidates = self
                     .provider
                     .get_candidates(package_name)
+                    .await
                     .unwrap_or_default();
 
                 // Store information about which solvables dependency information is easy to
@@ -126,23 +128,24 @@ impl<VS: VersionSet, N: PackageName, D: DependencyProvider<VS, N>> SolverCache<V
     ///
     /// If the provider has requested the solving process to be cancelled, the cancellation value
     /// will be returned as an `Err(...)`.
-    pub fn get_or_cache_matching_candidates(
+    pub async fn get_or_cache_matching_candidates(
         &self,
         version_set_id: VersionSetId,
     ) -> Result<&[SolvableId], Box<dyn Any>> {
         match self.version_set_candidates.get(&version_set_id) {
             Some(candidates) => Ok(candidates),
             None => {
-                let package_name = self.pool().resolve_version_set_package_name(version_set_id);
-                let version_set = self.pool().resolve_version_set(version_set_id);
-                let candidates = self.get_or_cache_candidates(package_name)?;
+                let pool = self.pool();
+                let package_name = pool.resolve_version_set_package_name(version_set_id);
+                let version_set = pool.resolve_version_set(version_set_id);
+                let candidates = self.get_or_cache_candidates(package_name).await?;
 
                 let matching_candidates = candidates
                     .candidates
                     .iter()
                     .copied()
                     .filter(|&p| {
-                        let version = self.pool().resolve_internal_solvable(p).solvable().inner();
+                        let version = pool.resolve_internal_solvable(p).solvable().inner();
                         version_set.contains(version)
                     })
                     .collect();
@@ -158,23 +161,24 @@ impl<VS: VersionSet, N: PackageName, D: DependencyProvider<VS, N>> SolverCache<V
     ///
     /// If the provider has requested the solving process to be cancelled, the cancellation value
     /// will be returned as an `Err(...)`.
-    pub fn get_or_cache_non_matching_candidates(
+    pub async fn get_or_cache_non_matching_candidates(
         &self,
         version_set_id: VersionSetId,
     ) -> Result<&[SolvableId], Box<dyn Any>> {
         match self.version_set_inverse_candidates.get(&version_set_id) {
             Some(candidates) => Ok(candidates),
             None => {
-                let package_name = self.pool().resolve_version_set_package_name(version_set_id);
-                let version_set = self.pool().resolve_version_set(version_set_id);
-                let candidates = self.get_or_cache_candidates(package_name)?;
+                let pool = self.pool();
+                let package_name = pool.resolve_version_set_package_name(version_set_id);
+                let version_set = pool.resolve_version_set(version_set_id);
+                let candidates = self.get_or_cache_candidates(package_name).await?;
 
                 let matching_candidates = candidates
                     .candidates
                     .iter()
                     .copied()
                     .filter(|&p| {
-                        let version = self.pool().resolve_internal_solvable(p).solvable().inner();
+                        let version = pool.resolve_internal_solvable(p).solvable().inner();
                         !version_set.contains(version)
                     })
                     .collect();
@@ -191,16 +195,18 @@ impl<VS: VersionSet, N: PackageName, D: DependencyProvider<VS, N>> SolverCache<V
     ///
     /// If the provider has requested the solving process to be cancelled, the cancellation value
     /// will be returned as an `Err(...)`.
-    pub fn get_or_cache_sorted_candidates(
+    pub async fn get_or_cache_sorted_candidates(
         &self,
         version_set_id: VersionSetId,
     ) -> Result<&[SolvableId], Box<dyn Any>> {
         match self.version_set_to_sorted_candidates.get(&version_set_id) {
             Some(candidates) => Ok(candidates),
             None => {
                 let package_name = self.pool().resolve_version_set_package_name(version_set_id);
-                let matching_candidates = self.get_or_cache_matching_candidates(version_set_id)?;
-                let candidates = self.get_or_cache_candidates(package_name)?;
+                let matching_candidates = self
+                    .get_or_cache_matching_candidates(version_set_id)
+                    .await?;
+                let candidates = self.get_or_cache_candidates(package_name).await?;
 
                 // Sort all the candidates in order in which they should be tried by the solver.
                 let mut sorted_candidates = Vec::new();
@@ -228,7 +234,7 @@ impl<VS: VersionSet, N: PackageName, D: DependencyProvider<VS, N>> SolverCache<V
     ///
     /// If the provider has requested the solving process to be cancelled, the cancellation value
     /// will be returned as an `Err(...)`.
-    pub fn get_or_cache_dependencies(
+    pub async fn get_or_cache_dependencies(
         &self,
         solvable_id: SolvableId,
     ) -> Result<&Dependencies, Box<dyn Any>> {
@@ -242,7 +248,7 @@ impl<VS: VersionSet, N: PackageName, D: DependencyProvider<VS, N>> SolverCache<V
                     return Err(value);
                 }
 
-                let dependencies = self.provider.get_dependencies(solvable_id);
+                let dependencies = self.provider.get_dependencies(solvable_id).await;
                 let dependencies_id = self.solvable_dependencies.alloc(dependencies);
                 self.solvable_to_dependencies
                     .insert_copy(solvable_id, dependencies_id);