Remove useless message handlers

These handlers are used to initiate the communication between
the content thread and the worker and they aren't used once the
document is loaded, hence we can remove them.

src/core/worker.js

@@ -87,8 +87,11 @@ class WorkerMessageHandler {
       setVerbosityLevel(data.verbosity);
     });
 
-    handler.on("GetDocRequest", function (data) {
-      return WorkerMessageHandler.createDocumentHandler(data, port);
+    handler.on("GetDocRequest", function ({ source, singleUse }) {
+      if (singleUse) {
+        handler.destroy();
+      }
+      return WorkerMessageHandler.createDocumentHandler(source, port);
     });
   }
 

src/display/api.js

@@ -216,6 +216,8 @@ const DefaultStandardFontDataFactory =
  *   when creating canvases. The default value is {new DOMCanvasFactory()}.
  * @property {Object} [filterFactory] - A factory instance that will be used
  *   to create SVG filters when rendering some images on the main canvas.
+ * @property {boolean} [singleUse] - When true the worker will be able to load
+ *   only one PDF document, using the `getDocument` method.
  */
 
 /**
@@ -346,12 +348,13 @@ function getDocument(src) {
       baseUrl: standardFontDataUrl,
     });
   }
-
   if (!worker) {
     const workerParams = {
       verbosity,
       port: GlobalWorkerOptions.workerPort,
+      singleUse: src.singleUse === true,
     };
+
     // Worker was not provided -- creating and owning our own. If message port
     // is specified in global worker options, using it.
     worker = workerParams.port
@@ -456,6 +459,12 @@ function getDocument(src) {
             throw new Error("Loading aborted");
           }
 
+          if (worker._singleUse) {
+            // We don't the messageHandler anymore.
+            worker._messageHandler.destroy();
+            worker._messageHandler = null;
+          }
+
           const messageHandler = new MessageHandler(
             docId,
             workerId,
@@ -493,7 +502,7 @@ async function _fetchDocument(worker, source) {
   }
   const workerId = await worker.messageHandler.sendWithPromise(
     "GetDocRequest",
-    source,
+    { source, singleUse: worker._singleUse },
     source.data ? [source.data.buffer] : null
   );
 
@@ -2029,6 +2038,7 @@ class PDFWorker {
     name = null,
     port = null,
     verbosity = getVerbosityLevel(),
+    singleUse = false,
   } = {}) {
     this.name = name;
     this.destroyed = false;
@@ -2038,6 +2048,7 @@ class PDFWorker {
     this._port = null;
     this._webWorker = null;
     this._messageHandler = null;
+    this._singleUse = singleUse;
 
     if (
       (typeof PDFJSDev === "undefined" || !PDFJSDev.test("MOZCENTRAL")) &&

web/app.js

@@ -1000,6 +1000,7 @@ const PDFViewerApplication = {
     const loadingTask = getDocument({
       ...apiParams,
       ...args,
+      singleUse: true,
     });
     this.pdfLoadingTask = loadingTask;