Initial rayon support: ParallelExtend + FromParallelIterator

This was a straightforward step towards jonhoo#14

.gitignore

@@ -1,4 +1,10 @@
+# Don't include build output
 /target
-**/*.rs.bk
+# We're a library--don't include our lockfile
 Cargo.lock
+# Don't include rustfmt backup files
+**/*.rs.bk
+
+# Don't include IDE configuration files
+.idea
 **/.vscode/*

Cargo.toml

@@ -26,6 +26,7 @@ sanitize = ['crossbeam-epoch/sanitize']
 crossbeam-epoch = "0.8.2"
 parking_lot = "0.10"
 num_cpus = "1.12.0"
+rayon = {version = "1.3", optional = true}
 serde = {version = "1.0.105", optional = true}
 
 [dependencies.ahash]

src/lib.rs

@@ -252,6 +252,9 @@ mod raw;
 mod set;
 mod set_ref;
 
+#[cfg(feature = "rayon")]
+mod rayon_impls;
+
 #[cfg(feature = "serde")]
 mod serde_impls;
 

src/rayon_impls.rs

@@ -0,0 +1,119 @@
+use crate::HashMap;
+use rayon::iter::{FromParallelIterator, IntoParallelIterator, ParallelExtend, ParallelIterator};
+use std::hash::{BuildHasher, Hash};
+
+impl<K, V, S> ParallelExtend<(K, V)> for HashMap<K, V, S>
+where
+    K: Clone + Hash + Ord + Send + Sync + 'static,
+    V: Send + Sync + 'static,
+    S: BuildHasher + Sync,
+{
+    // This is of limited use due to the `&mut self` parameter. See `par_extend_sync`
+    fn par_extend<I>(&mut self, par_iter: I)
+    where
+        I: IntoParallelIterator<Item = (K, V)>,
+    {
+        self.par_extend_sync(par_iter);
+    }
+}
+
+impl<K, V, S> HashMap<K, V, S>
+where
+    K: Clone + Hash + Ord + Send + Sync + 'static,
+    V: Send + Sync + 'static,
+    S: BuildHasher + Sync,
+{
+    // FIXME: Terrible name, just didn't want to shadow the rayon name
+    fn par_extend_sync<I>(&self, par_iter: I)
+    where
+        I: IntoParallelIterator<Item = (K, V)>,
+    {
+        par_iter.into_par_iter().for_each(|(k, v)| {
+            // Unfortunate that we need to create a guard for each insert operation
+            // Ideally we'd create a guard for each `rayon` worker thread instead
+            // Perhaps this could be done with a thread local?
+            let guard = self.guard();
+            self.insert(k, v, &guard);
+        });
+    }
+}
+
+impl<K, V> FromParallelIterator<(K, V)> for HashMap<K, V, crate::DefaultHashBuilder>
+where
+    K: Clone + Hash + Ord + Send + Sync + 'static,
+    V: Send + Sync + 'static,
+{
+    fn from_par_iter<I>(par_iter: I) -> Self
+    where
+        I: IntoParallelIterator<Item = (K, V)>,
+    {
+        let mut created_map = HashMap::new();
+        created_map.par_extend(par_iter);
+        created_map
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::HashMap;
+    use rayon::iter::{FromParallelIterator, IntoParallelIterator, ParallelExtend};
+
+    #[test]
+    fn parallel_extend_by_nothing() {
+        let to_extend_with = Vec::new();
+
+        let mut map = HashMap::new();
+        let guard = map.guard();
+        map.insert(1, 2, &guard);
+        map.insert(3, 4, &guard);
+
+        map.par_extend(to_extend_with.into_par_iter());
+
+        assert_eq!(map.len(), 2);
+
+        assert_eq!(map.get(&1, &guard), Some(&2));
+        assert_eq!(map.get(&3, &guard), Some(&4));
+    }
+
+    #[test]
+    fn parallel_extend_by_a_bunch() {
+        let mut to_extend_with = Vec::new();
+        for i in 0..100 {
+            to_extend_with.push((i + 100, i * 10));
+        }
+
+        let mut map = HashMap::new();
+        let guard = map.guard();
+        map.insert(1, 2, &guard);
+        map.insert(3, 4, &guard);
+
+        map.par_extend(to_extend_with.into_par_iter());
+        assert_eq!(map.len(), 102);
+
+        assert_eq!(map.get(&1, &guard), Some(&2));
+        assert_eq!(map.get(&3, &guard), Some(&4));
+        assert_eq!(map.get(&100, &guard), Some(&0));
+        assert_eq!(map.get(&199, &guard), Some(&990));
+    }
+
+    #[test]
+    fn from_empty_parallel_iter() {
+        let to_create_from: Vec<(i32, i32)> = Vec::new();
+        let created_map: HashMap<i32, i32> = HashMap::from_par_iter(to_create_from.into_par_iter());
+        assert_eq!(created_map.len(), 0);
+    }
+
+    #[test]
+    fn from_large_parallel_iter() {
+        let mut to_create_from: Vec<(i32, i32)> = Vec::new();
+        for i in 0..100 {
+            to_create_from.push((i + 100, i * 10));
+        }
+        let created_map: HashMap<i32, i32> = HashMap::from_par_iter(to_create_from.into_par_iter());
+        assert_eq!(created_map.len(), 100);
+
+        let guard = created_map.guard();
+        assert_eq!(created_map.get(&100, &guard), Some(&0));
+        assert_eq!(created_map.get(&199, &guard), Some(&990));
+    }
+}