Add quadtree nearestToPoint, and Readwrite locking (#217)

orx-quadtree/src/jvmMain/kotlin/ReadwriteQuadtree.kt

@@ -0,0 +1,44 @@
+package org.openrndr.extra.quadtree
+
+import org.openrndr.math.Vector2
+import java.util.concurrent.locks.ReentrantReadWriteLock
+import kotlin.concurrent.read
+import kotlin.concurrent.write
+
+/**
+ * Wraps a quadtree with a ReentrantReadWriteLock, which allows multiple concurrent
+ * readers or one writer at a time.
+ */
+class ReadwriteQuadtree<T>(val qt: Quadtree<T>) : IQuadtree<T> {
+    val lock = ReentrantReadWriteLock()
+
+    override fun clear() {
+        lock.write {
+            qt.clear()
+        }
+    }
+
+    override fun nearestToPoint(point: Vector2, radius: Double): QuadtreeQuery<T>? {
+        lock.read {
+            return qt.nearestToPoint(point, radius)
+        }
+    }
+
+    override fun nearest(element: T, radius: Double): QuadtreeQuery<T>? {
+        lock.read {
+            return qt.nearest(element, radius)
+        }
+    }
+
+    override fun insert(element: T): Boolean {
+        lock.write {
+            return qt.insert(element)
+        }
+    }
+
+    override fun findNode(element: T): Quadtree<T>? {
+        lock.read {
+            return qt.findNode(element)
+        }
+    }
+}