[BUGFIX] Grow the Uint16Array if the page size overflows 1MB

packages/@glimmer/program/lib/program.ts

@@ -37,6 +37,8 @@ export interface SerializedHeap {
 
 export type Placeholder = [number, () => number];
 
+const PAGE_SIZE = 0x100000;
+
 /**
  * The Heap is responsible for dynamically allocating
  * memory in which we read/write the VM's instructions
@@ -58,11 +60,12 @@ export type Placeholder = [number, () => number];
  * over them as you will have a bad memory access exception.
  */
 export class Heap implements CompileTimeHeap {
-  private heap: Uint16Array | Array<number>;
+  private heap: Uint16Array;
   private placeholders: Placeholder[] = [];
   private table: number[];
   private offset = 0;
   private handle = 0;
+  private capacity = PAGE_SIZE;
 
   constructor(serializedHeap?: SerializedHeap) {
     if (serializedHeap) {
@@ -71,16 +74,28 @@ export class Heap implements CompileTimeHeap {
       this.table = table;
       this.offset = this.heap.length;
       this.handle = handle;
+      this.capacity = 0;
     } else {
-      this.heap = new Uint16Array(0x100000);
+      this.heap = new Uint16Array(PAGE_SIZE);
       this.table = [];
     }
   }
 
   push(item: number): void {
+    this.sizeCheck();
     this.heap[this.offset++] = item;
   }
 
+  private sizeCheck() {
+    if (this.capacity === 0) {
+      let heap = slice(this.heap, 0, this.offset);
+      this.heap = new Uint16Array(heap.length + PAGE_SIZE);
+      this.heap.set(heap, 0);
+      this.capacity = PAGE_SIZE;
+    }
+    this.capacity--;
+  }
+
   getbyaddr(address: number): number {
     return this.heap[address];
   }
@@ -180,6 +195,7 @@ export class Heap implements CompileTimeHeap {
   }
 
   pushPlaceholder(valueFunc: () => number): void {
+    this.sizeCheck();
     let address = this.offset++;
     this.heap[address] = Size.MAX_SIZE;
     this.placeholders.push([address, valueFunc]);
@@ -196,11 +212,11 @@ export class Heap implements CompileTimeHeap {
     }
   }
 
-  capture(): SerializedHeap {
+  capture(offset = this.offset): SerializedHeap {
     this.patchPlaceholders();
 
     // Only called in eager mode
-    let buffer = slice(this.heap, 0, this.offset);
+    let buffer = slice(this.heap, 0, offset).buffer;
     return {
       handle: this.handle,
       table: this.table,
@@ -250,20 +266,16 @@ export class Program<Locator> extends WriteOnlyProgram {
   public constants: Constants<Locator>;
 }
 
-function slice(arr: Uint16Array | number[], start: number, end: number) {
-  if (arr instanceof Uint16Array) {
-    if (arr.slice !== undefined) {
-      return arr.slice(start, end).buffer;
-    }
-
-    let ret = new Uint16Array(end);
+function slice(arr: Uint16Array, start: number, end: number): Uint16Array {
+  if (arr.slice !== undefined) {
+    return arr.slice(start, end);
+  }
 
-    for (; start < end; start++) {
-      ret[start]  = arr[start];
-    }
+  let ret = new Uint16Array(end);
 
-    return ret.buffer;
+  for (; start < end; start++) {
+    ret[start]  = arr[start];
   }
 
-  return null;
+  return ret;
 }

packages/@glimmer/program/test/heap-test.ts

@@ -0,0 +1,38 @@
+import { Heap } from '@glimmer/program';
+
+QUnit.module('Heap');
+
+QUnit.test('Can grow', (assert) => {
+  let size = 0x100000;
+  let heap = new Heap();
+
+  let i = 0;
+
+  while (i !== (size - 1)) {
+    heap.push(1);
+    i++;
+  }
+
+  // Should grow here
+  heap.push(10);
+
+  // Slices the buffer. Passing MAX_SAFE_INTEGER ensures
+  // we get the whole thing out
+  let serialized = heap.capture(Number.MAX_SAFE_INTEGER);
+  let serializedHeap = new Uint16Array(serialized.buffer);
+  assert.equal(serializedHeap.length, size);
+  assert.equal(serializedHeap[size - 1], 10);
+
+  heap.push(11);
+
+  serialized = heap.capture(Number.MAX_SAFE_INTEGER);
+  serializedHeap = new Uint16Array(serialized.buffer);
+
+  if (serializedHeap.slice) {
+    assert.equal(serializedHeap.length, size * 2);
+  } else {
+    // IE11 only gives you a buffer with residents in the slots
+    assert.equal(serializedHeap.length, size + 1);
+  }
+  assert.equal(serializedHeap[size], 11);
+});