Convert PDFPageViewBuffer to a standard class, and use a Set internally

test/unit/base_viewer_spec.js

@@ -136,12 +136,12 @@ describe("BaseViewer", function () {
 
       // Ensure that decreasing the size will evict the correct views,
       // while re-ordering the remaining ones correctly.
-      buffer.resize(3, new Set([1, 2, 3]));
+      buffer.resize(3, new Set([1, 2, 5]));
 
       expect(buffer._buffer).toEqual([
         viewsMap.get(1),
         viewsMap.get(2),
-        viewsMap.get(3),
+        viewsMap.get(5),
       ]);
     });
 

test/unit/ui_utils_spec.js

@@ -21,7 +21,6 @@ import {
   getVisibleElements,
   isPortraitOrientation,
   isValidRotation,
-  moveToEndOfArray,
   parseQueryString,
   waitOnEventOrTimeout,
   WaitOnType,
@@ -864,44 +863,4 @@ describe("ui_utils", function () {
       });
     });
   });
-
-  describe("moveToEndOfArray", function () {
-    it("works on empty arrays", function () {
-      const data = [];
-      moveToEndOfArray(data, function () {});
-      expect(data).toEqual([]);
-    });
-
-    it("works when moving everything", function () {
-      const data = [1, 2, 3, 4, 5];
-      moveToEndOfArray(data, function () {
-        return true;
-      });
-      expect(data).toEqual([1, 2, 3, 4, 5]);
-    });
-
-    it("works when moving some things", function () {
-      const data = [1, 2, 3, 4, 5];
-      moveToEndOfArray(data, function (x) {
-        return x % 2 === 0;
-      });
-      expect(data).toEqual([1, 3, 5, 2, 4]);
-    });
-
-    it("works when moving one thing", function () {
-      const data = [1, 2, 3, 4, 5];
-      moveToEndOfArray(data, function (x) {
-        return x === 1;
-      });
-      expect(data).toEqual([2, 3, 4, 5, 1]);
-    });
-
-    it("works when moving nothing", function () {
-      const data = [1, 2, 3, 4, 5];
-      moveToEndOfArray(data, function (x) {
-        return x === 0;
-      });
-      expect(data).toEqual([1, 2, 3, 4, 5]);
-    });
-  });
 });

web/base_viewer.js

@@ -31,7 +31,6 @@ import {
   MAX_AUTO_SCALE,
   MAX_SCALE,
   MIN_SCALE,
-  moveToEndOfArray,
   PresentationModeState,
   RendererType,
   SCROLLBAR_PADDING,
@@ -92,18 +91,38 @@ const DEFAULT_CACHE_SIZE = 10;
  * @property {IL10n} l10n - Localization service.
  */
 
-function PDFPageViewBuffer(size) {
-  const data = [];
-  this.push = function (view) {
-    const i = data.indexOf(view);
-    if (i >= 0) {
-      data.splice(i, 1);
+class PDFPageViewBuffer {
+  // Here we rely on the fact that `Set`s preserve the insertion order.
+  #buf = new Set();
+
+  #size = 0;
+
+  constructor(size) {
+    this.#size = size;
+
+    if (
+      typeof PDFJSDev === "undefined" ||
+      PDFJSDev.test("!PRODUCTION || TESTING")
+    ) {
+      Object.defineProperty(this, "_buffer", {
+        get() {
+          return [...this.#buf];
+        },
+      });
     }
-    data.push(view);
-    if (data.length > size) {
-      data.shift().destroy();
+  }
+
+  push(view) {
+    const buf = this.#buf;
+    if (buf.has(view)) {
+      buf.delete(view); // Move the view to the "end" of the buffer.
+    }
+    buf.add(view);
+
+    if (buf.size > this.#size) {
+      this.#destroyFirstView();
     }
-  };
+  }
 
   /**
    * After calling resize, the size of the buffer will be `newSize`.
@@ -112,31 +131,38 @@ function PDFPageViewBuffer(size) {
    * `idsToKeep` has no impact on the final size of the buffer; if `idsToKeep`
    * is larger than `newSize`, some of those pages will be destroyed anyway.
    */
-  this.resize = function (newSize, idsToKeep = null) {
-    size = newSize;
+  resize(newSize, idsToKeep = null) {
+    this.#size = newSize;
+
+    const buf = this.#buf;
     if (idsToKeep) {
-      moveToEndOfArray(data, function (page) {
-        return idsToKeep.has(page.id);
-      });
+      const ii = buf.size;
+      let i = 1;
+      for (const view of buf) {
+        if (idsToKeep.has(view.id)) {
+          buf.delete(view); // Move the view to the "end" of the buffer.
+          buf.add(view);
+        }
+        if (++i > ii) {
+          break;
+        }
+      }
     }
-    while (data.length > size) {
-      data.shift().destroy();
+
+    while (buf.size > this.#size) {
+      this.#destroyFirstView();
     }
-  };
+  }
 
-  this.has = function (view) {
-    return data.includes(view);
-  };
+  has(view) {
+    return this.#buf.has(view);
+  }
 
-  if (
-    typeof PDFJSDev === "undefined" ||
-    PDFJSDev.test("!PRODUCTION || TESTING")
-  ) {
-    Object.defineProperty(this, "_buffer", {
-      get() {
-        return data.slice();
-      },
-    });
+  #destroyFirstView() {
+    const firstView = this.#buf.keys().next().value;
+
+    firstView?.destroy();
+    this.#buf.delete(firstView);
   }
 }
 
@@ -156,6 +182,8 @@ function isSameScale(oldScale, newScale) {
  * Simple viewer control to display PDF content/pages.
  */
 class BaseViewer {
+  #buffer = null;
+
   #scrollModePageState = null;
 
   /**
@@ -518,7 +546,7 @@ class BaseViewer {
       }
       // Add the page to the buffer at the start of drawing. That way it can be
       // evicted from the buffer and destroyed even if we pause its rendering.
-      this._buffer.push(pageView);
+      this.#buffer.push(pageView);
     };
     this.eventBus._on("pagerender", this._onBeforeDraw);
 
@@ -684,7 +712,7 @@ class BaseViewer {
     this._currentScale = UNKNOWN_SCALE;
     this._currentScaleValue = null;
     this._pageLabels = null;
-    this._buffer = new PDFPageViewBuffer(DEFAULT_CACHE_SIZE);
+    this.#buffer = new PDFPageViewBuffer(DEFAULT_CACHE_SIZE);
     this._location = null;
     this._pagesRotation = 0;
     this._optionalContentConfigPromise = null;
@@ -1153,7 +1181,7 @@ class BaseViewer {
       return;
     }
     const newCacheSize = Math.max(DEFAULT_CACHE_SIZE, 2 * numVisiblePages + 1);
-    this._buffer.resize(newCacheSize, visible.ids);
+    this.#buffer.resize(newCacheSize, visible.ids);
 
     this.renderingQueue.renderHighestPriority(visible);
 
@@ -1304,7 +1332,7 @@ class BaseViewer {
       return false;
     }
     const pageView = this._pages[pageNumber - 1];
-    return this._buffer.has(pageView);
+    return this.#buffer.has(pageView);
   }
 
   cleanup() {

web/ui_utils.js

@@ -906,27 +906,6 @@ class ProgressBar {
   }
 }
 
-/**
- * Moves all elements of an array that satisfy condition to the end of the
- * array, preserving the order of the rest.
- */
-function moveToEndOfArray(arr, condition) {
-  const moved = [],
-    len = arr.length;
-  let write = 0;
-  for (let read = 0; read < len; ++read) {
-    if (condition(arr[read])) {
-      moved.push(arr[read]);
-    } else {
-      arr[write] = arr[read];
-      ++write;
-    }
-  }
-  for (let read = 0; write < len; ++read, ++write) {
-    arr[write] = moved[read];
-  }
-}
-
 /**
  * Get the active or focused element in current DOM.
  *
@@ -1031,7 +1010,6 @@ export {
   MAX_AUTO_SCALE,
   MAX_SCALE,
   MIN_SCALE,
-  moveToEndOfArray,
   noContextMenuHandler,
   normalizeWheelEventDelta,
   normalizeWheelEventDirection,