From cf13130cba22d8ad783e6dac89ed7b9bbe6418d6 Mon Sep 17 00:00:00 2001
From: jeetiss <jeetiss@yandex.ru>
Date: Fri, 9 Apr 2021 12:43:43 +0300
Subject: [PATCH] use one pdf worker for all documents and for all rerenders

---
 src/Document.jsx      | 16 ++++++++++++++++
 src/Singleton.js      | 29 +++++++++++++++++++++++++++++
 src/Singleton.spec.js | 35 +++++++++++++++++++++++++++++++++++
 3 files changed, 80 insertions(+)
 create mode 100644 src/Singleton.js
 create mode 100644 src/Singleton.spec.js

diff --git a/src/Document.jsx b/src/Document.jsx
index c4d72c833..7c7c84bee 100644
--- a/src/Document.jsx
+++ b/src/Document.jsx
@@ -35,9 +35,15 @@ import {
   isFile as isFileProp,
   isRef,
 } from './shared/propTypes';
+import Singleton from './Singleton';
 
 const { PDFDataRangeTransport } = pdfjs;
 
+const workerProvider = new Singleton(
+  () => new pdfjs.PDFWorker({ name: 'react-pdf-worker' }),
+  (pdfjsWorker) => pdfjsWorker.destroy(),
+);
+
 export default class Document extends PureComponent {
   state = {
     pdf: null,
@@ -70,6 +76,11 @@ export default class Document extends PureComponent {
   linkService = new LinkService();
 
   componentDidMount() {
+    const { options } = this.props;
+    if (options && !options.worker) {
+      this.worker = workerProvider.acquire();
+    }
+
     this.loadDocument();
     this.setupLinkService();
   }
@@ -87,6 +98,7 @@ export default class Document extends PureComponent {
 
     // If loading is in progress, let's destroy it
     if (this.loadingTask) this.loadingTask.destroy();
+    if (this.worker) workerProvider.release();
   }
 
   loadDocument = async () => {
@@ -112,6 +124,10 @@ export default class Document extends PureComponent {
 
     const { options, onLoadProgress, onPassword } = this.props;
 
+    if (this.worker) {
+      options.worker = this.worker;
+    }
+
     try {
       // If another rendering is in progress, let's cancel it
       cancelRunningTask(this.runningTask);
diff --git a/src/Singleton.js b/src/Singleton.js
new file mode 100644
index 000000000..8d30b3df1
--- /dev/null
+++ b/src/Singleton.js
@@ -0,0 +1,29 @@
+class Singleton {
+  constructor(create, destroy) {
+    this.create = create;
+    this.destroy = destroy;
+
+    this.usageCount = 0;
+  }
+
+  acquire() {
+    if (!this.usageCount) {
+      this.instance = this.create();
+    }
+
+    this.usageCount += 1;
+
+    return this.instance;
+  }
+
+  release() {
+    this.usageCount -= 1;
+
+    if (this.usageCount <= 0) {
+      this.destroy(this.instance);
+      this.usageCount = 0;
+    }
+  }
+}
+
+export default Singleton;
diff --git a/src/Singleton.spec.js b/src/Singleton.spec.js
new file mode 100644
index 000000000..e54c103cb
--- /dev/null
+++ b/src/Singleton.spec.js
@@ -0,0 +1,35 @@
+import Singleton from './Singleton';
+
+describe('Singleton', () => {
+  it('should create instance only on first acquire call', () => {
+    const create = jest.fn();
+    const singleton = new Singleton(create, () => {});
+
+    singleton.acquire();
+    singleton.acquire();
+
+    expect(create).toHaveBeenCalledTimes(1);
+  });
+
+  it('should destroy instance when nobody uses it', () => {
+    const destroy = jest.fn();
+    const singleton = new Singleton(() => {}, destroy);
+
+    singleton.acquire();
+    singleton.acquire();
+    singleton.release();
+    singleton.release();
+
+    expect(destroy).toHaveBeenCalledTimes(1);
+  });
+
+  it('returns one instance for all acquire calls', () => {
+    const instance = {};
+    const singleton = new Singleton(() => instance, () => {});
+
+    const first = singleton.acquire();
+    const second = singleton.acquire();
+
+    expect(first).toEqual(second);
+  });
+});