Add SharedArrayBuffer support (#48)

This PR adds support for SharedArrayBuffer which is a fully compatible alternative to ArrayBuffer. The implementation follows the style used for the PR that added SharedArrayBuffer support in flatbush.

Author: trevorgerhardt

README.md

@@ -68,12 +68,14 @@ Alternatively, there's a browser bundle with a `KDBush` global variable:
 
 ## API
 
-#### new KDBush(numItems[, nodeSize, ArrayType])
+#### new KDBush(numItems[, nodeSize, ArrayType, ArrayBufferType])
 
 Creates an index that will hold a given number of points (`numItems`). Additionally accepts:
 
 - `nodeSize`: Size of the KD-tree node, `64` by default. Higher means faster indexing but slower search, and vise versa.
 - `ArrayType`: Array type to use for storing coordinate values. `Float64Array` by default, but if your coordinates are integer values, `Int32Array` makes the index faster and smaller.
+- `ArrayBufferType`: the array buffer type used to store data (`ArrayBuffer` by default);
+you may prefer `SharedArrayBuffer` if you want to share the index between threads (multiple `Worker`, `SharedWorker` or `ServiceWorker`).
 
 #### index.add(x, y)
 
@@ -89,7 +91,7 @@ Finds all items within a given radius from the query point and returns an array
 
 #### `KDBush.from(data)`
 
-Recreates a KDBush index from raw `ArrayBuffer` data
+Recreates a KDBush index from raw `ArrayBuffer` or `SharedArrayBuffer` data
 (that's exposed as `index.data` on a previously indexed KDBush instance).
 Very useful for transferring or sharing indices between threads or storing them in a file.
 

index.js

@@ -13,11 +13,11 @@ export default class KDBush {
 
     /**
      * Creates an index from raw `ArrayBuffer` data.
-     * @param {ArrayBuffer} data
+     * @param {ArrayBufferLike} data
      */
     static from(data) {
-        if (!(data instanceof ArrayBuffer)) {
-            throw new Error('Data must be an instance of ArrayBuffer.');
+        if (!(data instanceof ArrayBuffer) && !(data instanceof SharedArrayBuffer)) {
+            throw new Error('Data must be an instance of ArrayBuffer or SharedArrayBuffer.');
         }
         const [magic, versionAndType] = new Uint8Array(data, 0, 2);
         if (magic !== 0xdb) {
@@ -34,17 +34,18 @@ export default class KDBush {
         const [nodeSize] = new Uint16Array(data, 2, 1);
         const [numItems] = new Uint32Array(data, 4, 1);
 
-        return new KDBush(numItems, nodeSize, ArrayType, data);
+        return new KDBush(numItems, nodeSize, ArrayType, undefined, data);
     }
 
     /**
      * Creates an index that will hold a given number of items.
      * @param {number} numItems
      * @param {number} [nodeSize=64] Size of the KD-tree node (64 by default).
      * @param {TypedArrayConstructor} [ArrayType=Float64Array] The array type used for coordinates storage (`Float64Array` by default).
-     * @param {ArrayBuffer} [data] (For internal use only)
+     * @param {ArrayBufferConstructor} [ArrayBufferType=ArrayBuffer] The array buffer type used for storage (`ArrayBuffer` by default).
+     * @param {ArrayBufferLike} [data] (For internal use only)
      */
-    constructor(numItems, nodeSize = 64, ArrayType = Float64Array, data) {
+    constructor(numItems, nodeSize = 64, ArrayType = Float64Array, ArrayBufferType = ArrayBuffer, data) {
         if (isNaN(numItems) || numItems < 0) throw new Error(`Unexpected numItems value: ${numItems}.`);
 
         this.numItems = +numItems;
@@ -61,14 +62,14 @@ export default class KDBush {
             throw new Error(`Unexpected typed array class: ${ArrayType}.`);
         }
 
-        if (data && (data instanceof ArrayBuffer)) { // reconstruct an index from a buffer
+        if ((data instanceof ArrayBuffer) || (data instanceof SharedArrayBuffer)) { // reconstruct an index from a buffer
             this.data = data;
             this.ids = new this.IndexArrayType(this.data, HEADER_SIZE, numItems);
             this.coords = new this.ArrayType(this.data, HEADER_SIZE + idsByteSize + padCoords, numItems * 2);
             this._pos = numItems * 2;
             this._finished = true;
         } else { // initialize a new index
-            this.data = new ArrayBuffer(HEADER_SIZE + coordsByteSize + idsByteSize + padCoords);
+            this.data = new ArrayBufferType(HEADER_SIZE + coordsByteSize + idsByteSize + padCoords);
             this.ids = new this.IndexArrayType(this.data, HEADER_SIZE, numItems);
             this.coords = new this.ArrayType(this.data, HEADER_SIZE + idsByteSize + padCoords, numItems * 2);
             this._pos = 0;

test.js

@@ -27,8 +27,8 @@ const coords = [
     53,49,60,50,68,57,70,56,77,63,86,71,90,52,83,71,82,72,81,94,51,75,53,95,39,78,53,88,62,84,72,77,73,99,76,73,81,88,
     87,96,98,96,82];
 
-function makeIndex() {
-    const index = new KDBush(points.length, 10);
+function makeIndex(ArrayBufferType = ArrayBuffer) {
+    const index = new KDBush(points.length, 10, undefined, ArrayBufferType);
     for (const [x, y] of points) index.add(x, y);
     return index.finish();
 }
@@ -120,6 +120,17 @@ test('does not complain about zero items', () => {
     });
 });
 
+test('creates an index using SharedArrayBuffer', () => {
+    const index = makeIndex(SharedArrayBuffer);
+    assert(index.data instanceof SharedArrayBuffer);
+});
+
+test('reconstructs an index from a SharedArrayBuffer', () => {
+    const index = makeIndex(SharedArrayBuffer);
+    const index2 = KDBush.from(index.data);
+    assert.deepEqual(index, index2);
+});
+
 function sqDist(a, b) {
     const dx = a[0] - b[0];
     const dy = a[1] - b[1];