diff --git a/Cargo.toml b/Cargo.toml
index 441d9bd..200b7a9 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,6 +9,7 @@ edition = "2018"
 indicatif = { version = "0.15", optional = true }
 num_cpus = "1.13"
 ordered-float = "2.0"
+parking_lot = "0.11"
 rand = { version = "0.8", features = ["small_rng"] }
 rayon = "1.5"
 serde = { version = "1.0.118", features = ["derive"], optional = true }
diff --git a/src/lib.rs b/src/lib.rs
index 357ca07..af7ed2d 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,13 +1,16 @@
-use std::cmp::{max, min, Ordering, Reverse};
+use std::cmp::{max, Ordering, Reverse};
 use std::collections::BinaryHeap;
 use std::collections::HashSet;
+#[cfg(feature = "indicatif")]
+use std::sync::atomic::{self, AtomicUsize};
 
 #[cfg(feature = "indicatif")]
 use indicatif::ProgressBar;
 use ordered_float::OrderedFloat;
+use parking_lot::{Mutex, RwLock};
 use rand::rngs::SmallRng;
 use rand::SeedableRng;
-use rayon::iter::{IntoParallelRefMutIterator, ParallelIterator};
+use rayon::iter::{IntoParallelIterator, ParallelIterator};
 #[cfg(feature = "serde")]
 use serde::{Deserialize, Serialize};
 
@@ -125,6 +128,7 @@ where
         let ef_search = builder.ef_search.unwrap_or(100);
         let ef_construction = builder.ef_construction.unwrap_or(100);
         let ml = builder.ml.unwrap_or_else(|| (M as f32).ln());
+        let heuristic = builder.heuristic;
         let mut rng = match builder.seed {
             Some(seed) => SmallRng::seed_from_u64(seed),
             None => SmallRng::from_entropy(),
@@ -136,6 +140,7 @@ where
         if let Some(bar) = &progress {
             bar.set_draw_delta(1_000);
             bar.set_length(points.len() as u64);
+            bar.set_message("Build index (preparation)");
         }
 
         if points.is_empty() {
@@ -220,88 +225,67 @@ where
         // Insert the first point so that we have an enter point to start searches with.
 
         let mut layers = vec![vec![]; top.0];
-        let mut zero = Vec::with_capacity(points.len());
-        zero.push(ZeroNode::default());
+        let zero = points
+            .iter()
+            .map(|_| RwLock::new(ZeroNode::default()))
+            .collect::<Vec<_>>();
 
-        let mut insertion = Search {
-            ef: ef_construction,
-            visited: Visited::with_capacity(points.len()),
-            ..Default::default()
-        };
-
-        let mut pool = SearchPool {
-            pool: Vec::new(),
-            len: points.len(),
-        };
-
-        let mut batch = Vec::new();
-        let mut done = Vec::new();
-        let max_batch_len = num_cpus::get() * 4;
-        for (layer, mut range) in ranges {
+        let pool = SearchPool::new(points.len());
+        #[cfg(feature = "indicatif")]
+        let done = AtomicUsize::new(0);
+        for (layer, range) in ranges {
             let num = if layer.0 > 0 { M } else { M * 2 };
             #[cfg(feature = "indicatif")]
             if let Some(bar) = &progress {
                 bar.set_message(&format!("Building index (layer {})", layer.0));
             }
 
-            while range.start < range.end {
-                let len = min(range.len(), max_batch_len);
-                batch.clear();
-                batch.extend(
-                    nodes[range.start..(range.start + len)]
-                        .iter()
-                        .map(|&(_, pid)| (pid, pool.pop())),
-                );
+            nodes[range].into_par_iter().for_each(|(_, pid)| {
+                let (mut search, mut insertion) = pool.pop();
+                let point = &points.as_slice()[*pid];
+                search.reset();
+                search.push(PointId(0), point, &points);
 
-                batch.par_iter_mut().for_each(|(pid, search)| {
-                    let point = &points[*pid];
-                    search.push(PointId(0), point, &points);
-                    for cur in top.descend() {
-                        search.ef = if cur <= layer { ef_construction } else { 1 };
-                        match cur > layer {
-                            true => {
-                                search.search(point, layers[cur.0 - 1].as_slice(), &points, num);
-                                search.cull();
-                            }
-                            false => {
-                                search.search(point, zero.as_slice(), &points, num);
-                                break;
-                            }
+                for cur in top.descend() {
+                    search.ef = if cur <= layer { ef_construction } else { 1 };
+                    match cur > layer {
+                        true => {
+                            search.search(point, layers[cur.0 - 1].as_slice(), &points, num);
+                            search.cull();
+                        }
+                        false => {
+                            search.search(point, zero.as_slice(), &points, num);
+                            break;
                         }
                     }
-                });
-
-                done.clear();
-                for (pid, mut search) in batch.drain(..) {
-                    for added in done.iter().copied() {
-                        search.push(added, &points[pid], &points);
-                    }
-
-                    insert(
-                        pid,
-                        &mut insertion,
-                        &mut search,
-                        &mut zero,
-                        &points,
-                        &builder.heuristic,
-                    );
-                    done.push(pid);
-                    pool.push(search);
                 }
 
+                insertion.ef = ef_construction;
+                insert(
+                    *pid,
+                    &mut insertion,
+                    &mut search,
+                    &zero,
+                    &points,
+                    &heuristic,
+                );
+
                 #[cfg(feature = "indicatif")]
                 if let Some(bar) = &progress {
-                    bar.inc(done.len() as u64);
+                    let value = done.fetch_add(1, atomic::Ordering::Relaxed);
+                    if value % 1000 == 0 {
+                        bar.set_position(value as u64);
+                    }
                 }
 
-                range.start += len;
-            }
+                pool.push((search, insertion));
+            });
 
             // For layers above the zero layer, make a copy of the current state of the zero layer
             // with `nearest` truncated to `M` elements.
             if layer.0 > 0 {
                 let mut upper = Vec::with_capacity(zero.len());
-                upper.extend(zero.iter().map(UpperNode::from_zero));
+                upper.extend(zero.iter().map(|zero| UpperNode::from_zero(&zero.read())));
                 layers[layer.0 - 1] = upper;
             }
         }
@@ -314,7 +298,7 @@ where
         (
             Self {
                 ef_search,
-                zero,
+                zero: zero.into_iter().map(|node| node.into_inner()).collect(),
                 points,
                 layers,
             },
@@ -382,14 +366,14 @@ fn insert<P: Point>(
     new: PointId,
     insertion: &mut Search,
     search: &mut Search,
-    layer: &mut Vec<ZeroNode>,
+    layer: &[RwLock<ZeroNode>],
     points: &[P],
     heuristic: &Option<Heuristic>,
 ) {
-    layer.push(ZeroNode::default());
+    let mut node = layer[new].write();
     let found = match heuristic {
         None => search.select_simple(M * 2),
-        Some(heuristic) => search.select_heuristic(&points[new], &layer, points, *heuristic),
+        Some(heuristic) => search.select_heuristic(&points[new], layer, points, *heuristic),
     };
 
     // Just make sure the candidates are all unique
@@ -404,19 +388,22 @@ fn insert<P: Point>(
         if let Some(heuristic) = heuristic {
             let found = insertion.add_neighbor_heuristic(
                 new,
-                layer.as_slice().nearest_iter(pid),
+                layer.nearest_iter(pid),
                 layer,
                 &points[pid],
                 points,
                 *heuristic,
             );
 
-            layer[pid].rewrite(found.iter().map(|candidate| candidate.pid));
-            layer[new].set(i, pid);
+            layer[pid]
+                .write()
+                .rewrite(found.iter().map(|candidate| candidate.pid));
+            node.set(i, pid);
         } else {
             // Find the correct index to insert at to keep the neighbor's neighbors sorted
             let old = &points[pid];
             let idx = layer[pid]
+                .read()
                 .binary_search_by(|third| {
                     // `third` here is one of the neighbors of the new node's neighbor.
                     let third = match third {
@@ -429,30 +416,34 @@ fn insert<P: Point>(
                 })
                 .unwrap_or_else(|e| e);
 
-            layer[pid].insert(idx, new);
-            layer[new].set(i, pid);
+            layer[pid].write().insert(idx, new);
+            node.set(i, pid);
         }
     }
 }
 
 struct SearchPool {
-    pool: Vec<Search>,
+    pool: Mutex<Vec<(Search, Search)>>,
     len: usize,
 }
 
 impl SearchPool {
-    fn pop(&mut self) -> Search {
-        match self.pool.pop() {
-            Some(mut search) => {
-                search.reset();
-                search
-            }
-            None => Search::new(self.len),
+    fn new(len: usize) -> Self {
+        Self {
+            pool: Mutex::new(Vec::new()),
+            len,
         }
     }
 
-    fn push(&mut self, search: Search) {
-        self.pool.push(search);
+    fn pop(&self) -> (Search, Search) {
+        match self.pool.lock().pop() {
+            Some(res) => res,
+            None => (Search::new(self.len), Search::new(self.len)),
+        }
+    }
+
+    fn push(&self, item: (Search, Search)) {
+        self.pool.lock().push(item);
     }
 }
 
@@ -516,11 +507,11 @@ impl Search {
         }
     }
 
-    fn add_neighbor_heuristic<P: Point>(
+    fn add_neighbor_heuristic<L: Layer, P: Point>(
         &mut self,
         new: PointId,
         current: impl Iterator<Item = PointId>,
-        layer: &[ZeroNode],
+        layer: L,
         point: &P,
         points: &[P],
         params: Heuristic,
@@ -530,16 +521,16 @@ impl Search {
         for pid in current {
             self.push(pid, point, points);
         }
-        self.select_heuristic(point, &layer, points, params)
+        self.select_heuristic(point, layer, points, params)
     }
 
     /// Heuristically sort and truncate neighbors in `self.nearest`
     ///
     /// Invariant: `self.nearest` must be in sorted (nearest first) order.
-    fn select_heuristic<P: Point>(
+    fn select_heuristic<L: Layer, P: Point>(
         &mut self,
         point: &P,
-        layer: &[ZeroNode],
+        layer: L,
         points: &[P],
         params: Heuristic,
     ) -> &[Candidate] {
diff --git a/src/types.rs b/src/types.rs
index 0c3af9f..4431342 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -1,7 +1,8 @@
 use std::hash::Hash;
-use std::ops::{Deref, Index, IndexMut};
+use std::ops::{Deref, Index};
 
 use ordered_float::OrderedFloat;
+use parking_lot::{MappedRwLockReadGuard, RwLock, RwLockReadGuard};
 use rand::rngs::SmallRng;
 use rand::Rng;
 #[cfg(feature = "serde")]
@@ -69,11 +70,11 @@ impl UpperNode {
     }
 }
 
-impl Layer for &[UpperNode] {
-    fn nearest_iter(&self, pid: PointId) -> NearestIter<'_> {
-        NearestIter {
-            nearest: &self[pid.0 as usize].0,
-        }
+impl<'a> Layer for &'a [UpperNode] {
+    type Slice = &'a [PointId];
+
+    fn nearest_iter(&self, pid: PointId) -> NearestIter<Self::Slice> {
+        NearestIter::new(&self[pid.0 as usize].0)
     }
 }
 
@@ -128,32 +129,63 @@ impl Deref for ZeroNode {
     }
 }
 
-impl Layer for &[ZeroNode] {
-    fn nearest_iter(&self, pid: PointId) -> NearestIter<'_> {
-        NearestIter {
-            nearest: &self[pid.0 as usize].0,
-        }
+impl<'a> Layer for &'a [ZeroNode] {
+    type Slice = &'a [PointId];
+
+    fn nearest_iter(&self, pid: PointId) -> NearestIter<Self::Slice> {
+        NearestIter::new(&self[pid.0 as usize])
+    }
+}
+
+impl<'a> Layer for &'a [RwLock<ZeroNode>] {
+    type Slice = MappedRwLockReadGuard<'a, [PointId]>;
+
+    fn nearest_iter(&self, pid: PointId) -> NearestIter<Self::Slice> {
+        NearestIter::new(RwLockReadGuard::map(
+            self[pid.0 as usize].read(),
+            Deref::deref,
+        ))
     }
 }
 
 pub(crate) trait Layer {
-    fn nearest_iter(&self, pid: PointId) -> NearestIter<'_>;
+    type Slice: Deref<Target = [PointId]>;
+    fn nearest_iter(&self, pid: PointId) -> NearestIter<Self::Slice>;
 }
 
-pub(crate) struct NearestIter<'a> {
-    nearest: &'a [PointId],
+pub(crate) struct NearestIter<T> {
+    node: T,
+    cur: usize,
 }
 
-impl<'a> Iterator for NearestIter<'a> {
+impl<T> NearestIter<T>
+where
+    T: Deref<Target = [PointId]>,
+{
+    fn new(node: T) -> Self {
+        Self { node, cur: 0 }
+    }
+}
+
+impl<T> Iterator for NearestIter<T>
+where
+    T: Deref<Target = [PointId]>,
+{
     type Item = PointId;
 
     fn next(&mut self) -> Option<Self::Item> {
-        let (&first, rest) = self.nearest.split_first()?;
-        if !first.is_valid() {
+        if self.cur >= self.node.len() {
             return None;
         }
-        self.nearest = rest;
-        Some(first)
+
+        let item = self.node[self.cur];
+        if !item.is_valid() {
+            self.cur = self.node.len();
+            return None;
+        }
+
+        self.cur += 1;
+        Some(item)
     }
 }
 
@@ -230,14 +262,6 @@ impl<P> Index<PointId> for Hnsw<P> {
     }
 }
 
-impl<P: Point> Index<PointId> for Vec<P> {
-    type Output = P;
-
-    fn index(&self, index: PointId) -> &Self::Output {
-        &self[index.0 as usize]
-    }
-}
-
 impl<P: Point> Index<PointId> for [P] {
     type Output = P;
 
@@ -246,18 +270,12 @@ impl<P: Point> Index<PointId> for [P] {
     }
 }
 
-impl Index<PointId> for Vec<ZeroNode> {
-    type Output = ZeroNode;
+impl Index<PointId> for [RwLock<ZeroNode>] {
+    type Output = RwLock<ZeroNode>;
 
     fn index(&self, index: PointId) -> &Self::Output {
         &self[index.0 as usize]
     }
 }
 
-impl IndexMut<PointId> for Vec<ZeroNode> {
-    fn index_mut(&mut self, index: PointId) -> &mut Self::Output {
-        &mut self[index.0 as usize]
-    }
-}
-
 pub(crate) const INVALID: PointId = PointId(u32::MAX);