Simplify tree traversal algorithms

georust · Nov 5, 2024 · 537b664 · 537b664
1 parent 608244c
commit 537b664
Showing 1 changed file with 37 additions and 63 deletions.
diff --git a/geo/src/algorithm/bool_ops/mod.rs b/geo/src/algorithm/bool_ops/mod.rs
@@ -137,6 +137,16 @@ pub enum OpType {
     Xor,
 }
 
+// Recursive algorithms can benefit from grouping those parameters which are constant over
+// the whole algorithm to reduce the overhead of the recursive calls, in this case the single-
+// and multi-threaded unary union tree traversals
+#[derive(Debug)]
+struct Ops<I, F, R> {
+    init: I,
+    fold: F,
+    reduce: R,
+}
+
 /// Efficient [BooleanOps::union] of adjacent / overlapping geometries
 ///
 /// For geometries with a high degree of overlap or adjacency
@@ -180,44 +190,26 @@ pub trait UnaryUnion {
 // Though the operation is carried out via fold() over the tree iterator, there are two actual nested operations:
 // "fold" operations on leaf nodes build up output MultiPolygons by adding Polygons to them via union and
 // "reduce" operations on parent nodes combine these output MultiPolygons from leaf operations by recursion
-fn bottom_up_fold_reduce<T, S, I, F, R>(tree: &RTree<T>, init: I, fold: F, reduce: R) -> S
+fn bottom_up_fold_reduce<T, S, I, F, R>(ops: &mut Ops<I, F, R>, parent: &ParentNode<T>) -> S
 where
     T: RTreeObject,
     I: FnMut() -> S,
     F: FnMut(S, &T) -> S,
     R: FnMut(S, S) -> S,
 {
-    // recursive algorithms can benefit from grouping those parameters which are constant over
-    // the whole algorithm to reduce the overhead of the recursive calls
-    struct Ops<I, F, R> {
-        init: I,
-        fold: F,
-        reduce: R,
-    }
-
-    fn inner<T, S, I, F, R>(ops: &mut Ops<I, F, R>, parent: &ParentNode<T>) -> S
-    where
-        T: RTreeObject,
-        I: FnMut() -> S,
-        F: FnMut(S, &T) -> S,
-        R: FnMut(S, S) -> S,
-    {
-        parent
-            .children()
-            .iter()
-            .fold((ops.init)(), |accum, child| match child {
-                RTreeNode::Leaf(value) => (ops.fold)(accum, value),
-                RTreeNode::Parent(parent) => {
-                    let value = inner(ops, parent);
-                    (ops.reduce)(accum, value)
-                }
-            })
-    }
-    let mut ops = Ops { init, fold, reduce };
-    inner(&mut ops, tree.root())
+    parent
+        .children()
+        .iter()
+        .fold((ops.init)(), |accum, child| match child {
+            RTreeNode::Leaf(value) => (ops.fold)(accum, value),
+            RTreeNode::Parent(parent) => {
+                let value = bottom_up_fold_reduce(ops, parent);
+                (ops.reduce)(accum, value)
+            }
+        })
 }
 
-fn par_bottom_up_fold_reduce<T, S, I, F, R>(tree: &RTree<T>, init: I, fold: F, reduce: R) -> S
+fn par_bottom_up_fold_reduce<T, S, I, F, R>(ops: &Ops<I, F, R>, parent: &ParentNode<T>) -> S
 where
     T: RTreeObject,
     RTreeNode<T>: Send + Sync,
@@ -226,37 +218,17 @@ where
     F: Fn(S, &T) -> S + Send + Sync,
     R: Fn(S, S) -> S + Send + Sync,
 {
-    // recursive algorithms can benefit from grouping those parameters which are constant over
-    // the whole algorithm to reduce the overhead of the recursive calls
-    struct Ops<I, F, R> {
-        init: I,
-        fold: F,
-        reduce: R,
-    }
-
-    fn inner<T, S, I, F, R>(ops: &Ops<I, F, R>, parent: &ParentNode<T>) -> S
-    where
-        T: RTreeObject,
-        RTreeNode<T>: Send + Sync,
-        S: Send,
-        I: Fn() -> S + Send + Sync,
-        F: Fn(S, &T) -> S + Send + Sync,
-        R: Fn(S, S) -> S + Send + Sync,
-    {
-        parent
-            .children()
-            .into_par_iter()
-            .fold(&ops.init, |accum, child| match child {
-                RTreeNode::Leaf(value) => (ops.fold)(accum, value),
-                RTreeNode::Parent(parent) => {
-                    let value = inner(ops, parent);
-                    (ops.reduce)(accum, value)
-                }
-            })
-            .reduce(&ops.init, &ops.reduce)
-    }
-    let ops = Ops { init, fold, reduce };
-    inner(&ops, tree.root())
+    parent
+        .children()
+        .into_par_iter()
+        .fold(&ops.init, |accum, child| match child {
+            RTreeNode::Leaf(value) => (ops.fold)(accum, value),
+            RTreeNode::Parent(parent) => {
+                let value = par_bottom_up_fold_reduce(ops, parent);
+                (ops.reduce)(accum, value)
+            }
+        })
+        .reduce(&ops.init, &ops.reduce)
 }
 
 impl<T: BoolOpsNum> BooleanOps for Polygon<T> {
@@ -300,7 +272,8 @@ where
                 .map(|p| CachedEnvelope::new(ObjectRef::new(p)))
                 .collect(),
         );
-        bottom_up_fold_reduce(&rtree, init, fold, reduce)
+        let mut ops = Ops { init, fold, reduce };
+        bottom_up_fold_reduce(&mut ops, rtree.root())
     }
 }
 
@@ -337,6 +310,7 @@ where
                 .collect(),
         );
 
-        par_bottom_up_fold_reduce(&rtree, init, fold, reduce)
+        let ops = Ops { init, fold, reduce };
+        par_bottom_up_fold_reduce(&ops, rtree.root())
     }
 }