[api-minor] Simplify clean-up of page resources after rendering

After PR 2317, which landed in 2012, we'd immediately clean-up after rendering for pages with large image resources. This had the effect that re-rendering, e.g. after zooming, would force us to re-parse the entire page which could easily lead to bad performance.
In PR 16108, which landed in 2023, we tried to lessen the impact of that by slightly delaying clean-up however that's obviously not a perfect solution (and it increased the complexity of the relevant code).

Furthermore, the condition for this "immediate" clean-up seems a bit arbitrary to me since a page could easily contain a large number of smaller images whose total size vastly exceeds the threshold.

Hence this patch, which suggests that we remove the conditional and delayed clean-up after rendering. Compared to the situation back in 2012, a number of things have improved since:
 - We have *multiple* caches for repeated image-resources on the worker-thread[1], which helps reduce overall memory usage and improves performance.
 - We downsize huge images on the worker-thread, which means that the images we're using on the main-thread cannot be arbitrarily large.
 - The amount of available RAM on devices should be a lot higher, since more than a decade has passed.

A future improvement here, for more resource constrained environments, could be to instead clean-up when actually needed using e.g. `WeakRef`s (see issue 18148).

---
[1] More specifically:
 - `LocalImageCache`, which caches image-data by /Name and /Ref on the `PartialEvaluator.prototype.getOperatorList` level.
 - `RegionalImageCache`, which caches image-data by /Ref on the `PartialEvaluator`-instance (i.e. at the page) level.
 - `GlobalImageCache`, which caches image-data by /Ref globally at the document level.

src/core/image_utils.js

@@ -13,12 +13,7 @@
  * limitations under the License.
  */
 
-import {
+import { assert, unreachable, warn } from "../shared/util.js";
-  assert,
-  MAX_IMAGE_SIZE_TO_CACHE,
-  unreachable,
-  warn,
-} from "../shared/util.js";
 import { RefSet, RefSetCache } from "./primitives.js";
 
 class BaseLocalCache {
@@ -179,7 +174,7 @@ class GlobalImageCache {
 
   static MIN_IMAGES_TO_CACHE = 10;
 
-  static MAX_BYTE_SIZE = 5 * MAX_IMAGE_SIZE_TO_CACHE;
+  static MAX_BYTE_SIZE = 5e7; // Fifty megabytes.
 
   #decodeFailedSet = new RefSet();
 

src/display/api.js

@@ -25,7 +25,6 @@ import {
   getVerbosityLevel,
   info,
   isNodeJS,
-  MAX_IMAGE_SIZE_TO_CACHE,
   RenderingIntentFlag,
   setVerbosityLevel,
   shadow,
@@ -72,7 +71,6 @@ import { XfaText } from "./xfa_text.js";
 
 const DEFAULT_RANGE_CHUNK_SIZE = 65536; // 2^16 = 65536
 const RENDERING_CANCELLED_TIMEOUT = 100; // ms
-const DELAYED_CLEANUP_TIMEOUT = 5000; // ms
 
 /**
  * @typedef { Int8Array | Uint8Array | Uint8ClampedArray |
@@ -1339,8 +1337,6 @@ class PDFDocumentProxy {
  * Proxy to a `PDFPage` in the worker thread.
  */
 class PDFPageProxy {
-  #delayedCleanupTimeout = null;
-
   #pendingCleanup = false;
 
   constructor(pageIndex, pageInfo, transport, pdfBug = false) {
@@ -1353,7 +1349,6 @@ class PDFPageProxy {
     this.commonObjs = transport.commonObjs;
     this.objs = new PDFObjects();
 
-    this._maybeCleanupAfterRender = false;
     this._intentStates = new Map();
     this.destroyed = false;
   }
@@ -1490,10 +1485,8 @@ class PDFPageProxy {
     );
     const { renderingIntent, cacheKey } = intentArgs;
     // If there was a pending destroy, cancel it so no cleanup happens during
-    // this call to render...
+    // this call to render.
     this.#pendingCleanup = false;
-    // ... and ensure that a delayed cleanup is always aborted.
-    this.#abortDelayedCleanup();
 
     optionalContentConfigPromise ||=
       this._transport.getOptionalContentConfig(renderingIntent);
@@ -1532,10 +1525,10 @@ class PDFPageProxy {
 
       // Attempt to reduce memory usage during *printing*, by always running
       // cleanup immediately once rendering has finished.
-      if (this._maybeCleanupAfterRender || intentPrint) {
+      if (intentPrint) {
         this.#pendingCleanup = true;
       }
-      this.#tryCleanup(/* delayed = */ !intentPrint);
+      this.#tryCleanup();
 
       if (error) {
         internalRenderTask.capability.reject(error);
@@ -1769,7 +1762,6 @@ class PDFPageProxy {
     }
     this.objs.clear();
     this.#pendingCleanup = false;
-    this.#abortDelayedCleanup();
 
     return Promise.all(waitOn);
   }
@@ -1783,7 +1775,7 @@ class PDFPageProxy {
    */
   cleanup(resetStats = false) {
     this.#pendingCleanup = true;
-    const success = this.#tryCleanup(/* delayed = */ false);
+    const success = this.#tryCleanup();
 
     if (resetStats && success) {
       this._stats &&= new StatTimer();
@@ -1793,25 +1785,12 @@ class PDFPageProxy {
 
   /**
    * Attempts to clean up if rendering is in a state where that's possible.
-   * @param {boolean} [delayed] - Delay the cleanup, to e.g. improve zooming
-   *   performance in documents with large images.
-   *   The default value is `false`.
    * @returns {boolean} Indicates if clean-up was successfully run.
    */
-  #tryCleanup(delayed = false) {
+  #tryCleanup() {
-    this.#abortDelayedCleanup();
-
     if (!this.#pendingCleanup || this.destroyed) {
       return false;
     }
-    if (delayed) {
-      this.#delayedCleanupTimeout = setTimeout(() => {
-        this.#delayedCleanupTimeout = null;
-        this.#tryCleanup(/* delayed = */ false);
-      }, DELAYED_CLEANUP_TIMEOUT);
-
-      return false;
-    }
     for (const { renderTasks, operatorList } of this._intentStates.values()) {
       if (renderTasks.size > 0 || !operatorList.lastChunk) {
         return false;
@@ -1823,13 +1802,6 @@ class PDFPageProxy {
     return true;
   }
 
-  #abortDelayedCleanup() {
-    if (this.#delayedCleanupTimeout) {
-      clearTimeout(this.#delayedCleanupTimeout);
-      this.#delayedCleanupTimeout = null;
-    }
-  }
-
   /**
    * @private
    */
@@ -1863,7 +1835,7 @@ class PDFPageProxy {
     }
 
     if (operatorListChunk.lastChunk) {
-      this.#tryCleanup(/* delayed = */ true);
+      this.#tryCleanup();
     }
   }
 
@@ -1926,7 +1898,7 @@ class PDFPageProxy {
             for (const internalRenderTask of intentState.renderTasks) {
               internalRenderTask.operatorListChanged();
             }
-            this.#tryCleanup(/* delayed = */ true);
+            this.#tryCleanup();
           }
 
           if (intentState.displayReadyCapability) {
@@ -2884,13 +2856,6 @@ class WorkerTransport {
 
       switch (type) {
         case "Image":
-          pageProxy.objs.resolve(id, imageData);
-
-          // Heuristic that will allow us not to store large data.
-          if (imageData?.dataLen > MAX_IMAGE_SIZE_TO_CACHE) {
-            pageProxy._maybeCleanupAfterRender = true;
-          }
-          break;
         case "Pattern":
           pageProxy.objs.resolve(id, imageData);
           break;

src/shared/util.js

@@ -28,8 +28,6 @@ const isNodeJS =
 const IDENTITY_MATRIX = [1, 0, 0, 1, 0, 0];
 const FONT_IDENTITY_MATRIX = [0.001, 0, 0, 0.001, 0, 0];
 
-const MAX_IMAGE_SIZE_TO_CACHE = 10e6; // Ten megabytes.
-
 // Represent the percentage of the height of a single-line field over
 // the font size. Acrobat seems to use this value.
 const LINE_FACTOR = 1.35;
@@ -1155,7 +1153,6 @@ export {
   isNodeJS,
   LINE_DESCENT_FACTOR,
   LINE_FACTOR,
-  MAX_IMAGE_SIZE_TO_CACHE,
   normalizeUnicode,
   objectFromMap,
   objectSize,