LUCENE-9067: Polygon2D#contains is now thread safe (#1040)

Use a byte to handle the logic if a point lies on the boundary.

lucene/CHANGES.txt

@@ -145,6 +145,8 @@ Other
 
 * LUCENE-8983: Add sandbox PhraseWildcardQuery to control multi-terms expansions in a phrase. (Bruno Roustant)
 
+* LUCENE-9067: Polygon2D#contains() is now thread safe. (Ignacio Vera)
+
 Build
 
 * Upgrade forbiddenapis to version 2.7; upgrade Groovy to 2.4.17.  (Uwe Schindler)

lucene/core/src/java/org/apache/lucene/geo/EdgeTree.java

@@ -17,7 +17,6 @@
 package org.apache.lucene.geo;
 
 import java.util.Arrays;
-import java.util.concurrent.atomic.AtomicBoolean;
 
 import static org.apache.lucene.geo.GeoUtils.lineCrossesLine;
 import static org.apache.lucene.geo.GeoUtils.lineCrossesLineWithBoundary;
@@ -38,7 +37,7 @@ import static org.apache.lucene.geo.GeoUtils.orient;
  *
  * @lucene.internal
  */
-public  class EdgeTree {
+public class EdgeTree {
     // lat-lon pair (in original order) of the two vertices
     final double y1, y2;
     final double x1, x2;
@@ -50,6 +49,10 @@ public  class EdgeTree {
     EdgeTree left;
     /** right child edge, or null */
     EdgeTree right;
+    /** helper bytes to signal if a point is on an edge, it is within the edge tree or disjoint */
+    final private static byte FALSE = 0x00;
+    final private static byte TRUE = 0x01;
+    final private static byte ON_EDGE = 0x02;
 
   EdgeTree(double x1, double y1, double x2, double y2, double low, double max) {
       this.y1 = y1;
@@ -61,7 +64,17 @@ public  class EdgeTree {
     }
 
   /**
-   * Returns true if the point crosses this edge subtree an odd number of times
+   * Returns true if the point is on an edge or crosses the edge subtree an odd number
+   * of times.
+   */
+  protected boolean contains(double x, double y) {
+    return containsPnPoly(x, y) > FALSE;
+  }
+
+  /**
+   * Returns byte 0x00 if the point crosses this edge subtree an even number of times.
+   * Returns byte 0x01 if the point crosses this edge subtree an odd number of times.
+   * Returns byte 0x02 if the point is on one of the edges.
    * <p>
    * See <a href="https://www.ecse.rpi.edu/~wrf/Research/Short_Notes/pnpoly.html">
    * https://www.ecse.rpi.edu/~wrf/Research/Short_Notes/pnpoly.html</a> for more information.
@@ -90,30 +103,35 @@ public  class EdgeTree {
   // THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
   // CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
   // IN THE SOFTWARE.
-  protected boolean contains(double x, double y, AtomicBoolean isOnEdge) {
-    boolean res = false;
-    if (isOnEdge.get() == false && y <= this.max) {
+  private byte containsPnPoly(double x, double y) {
+    byte res = FALSE;
+    if (y <= this.max) {
       if (y == this.y1 && y == this.y2 ||
           (y <= this.y1 && y >= this.y2) != (y >= this.y1 && y <= this.y2)) {
         if ((x == this.x1 && x == this.x2) ||
             ((x <= this.x1 && x >= this.x2) != (x >= this.x1 && x <= this.x2) &&
                 GeoUtils.orient(this.x1, this.y1, this.x2, this.y2, x, y) == 0)) {
-          // if its on the boundary return true
-          isOnEdge.set(true);
-          return true;
+          return ON_EDGE;
         } else if (this.y1 > y != this.y2 > y) {
-          res = x < (this.x2 - this.x1) * (y - this.y1) / (this.y2 - this.y1) + this.x1;
+          res = x < (this.x2 - this.x1) * (y - this.y1) / (this.y2 - this.y1) + this.x1 ? TRUE : FALSE;
         }
       }
       if (this.left != null) {
-        res ^= left.contains(x, y, isOnEdge);
+        res ^= left.containsPnPoly(x, y);
+        if ((res & 0x02) == 0x02) {
+          return ON_EDGE;
+        }
       }
 
       if (this.right != null && y >= this.low) {
-        res ^= right.contains(x, y, isOnEdge);
+        res ^= right.containsPnPoly(x, y);
+        if ((res & 0x02) == 0x02) {
+          return ON_EDGE;
+        }
       }
     }
-    return isOnEdge.get() || res;
+    assert res >= FALSE && res <= ON_EDGE;
+    return res;
   }
 
   /** returns true if the provided x, y point lies on the line */

lucene/core/src/java/org/apache/lucene/geo/Polygon2D.java

@@ -16,8 +16,6 @@
  */
 package org.apache.lucene.geo;
 
-import java.util.concurrent.atomic.AtomicBoolean;
-
 import org.apache.lucene.index.PointValues.Relation;
 
 /**
@@ -41,8 +39,6 @@ public class Polygon2D implements Component2D {
   final protected Component2D holes;
   /** Edges of the polygon represented as a 2-d interval tree.*/
   final EdgeTree tree;
-  /** helper boolean for points on boundary */
-  final private AtomicBoolean containsBoundary = new AtomicBoolean(false);
 
   protected Polygon2D(final double minX, final double maxX, final double minY, final double maxY, double[] x, double[] y, Component2D holes) {
     this.minY = minY;
@@ -92,8 +88,7 @@ public class Polygon2D implements Component2D {
   }
 
   private boolean internalContains(double x, double y) {
-    containsBoundary.set(false);
-    if (tree.contains(x, y, containsBoundary)) {
+    if (tree.contains(x, y)) {
       if (holes != null && holes.contains(x, y)) {
         return false;
       }