Fix Worker was terminated error when loading is cancelled
#20503
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Fixes mozilla#11595, where cancelling loading with `loadingTask.destroy()` before it finishes throws a `Worker was terminated` error that CANNOT be caught. When worker is terminated, an error is thrown here: https://github.com/mozilla/pdf.js/blob/6c746260a98766b8ece27018d2c48436cfcafa24/src/core/worker.js#L374 Then `onFailure` runs, in which we throw again via `ensureNotTerminated()`. However, this second error is never caught (and cannot be), resulting in console spam. There is no need to throw any additional errors since the termination is already reported [here](https://github.com/mozilla/pdf.js/blob/6c746260a98766b8ece27018d2c48436cfcafa24/src/core/worker.js#L371-L373), and `onFailure` is supposed to handle errors, not throw them.
Open
16 tasks
Contributor
|
Is it possible to write a test ? |
Contributor
Author
@calixteman I think the closest way would be something like the following: Codefunction makeAsyncCallback() {
let resolve;
const promise = new Promise(r => {
resolve = r;
});
const func = function () {
resolve();
};
return { func, promise };
}
function sleep(ms) {
return new Promise(resolve => setTimeout(resolve, ms));
}
function onUnhandledRejection(event) {
fail(event.reason || event);
}
it("no unhandled error is thrown when loading is cancelled", async function () {
if (isNodeJS) {
pending("Worker is not supported in Node.js.");
}
const { func: onProgress, promise: waitForProgress } = makeAsyncCallback();
window.addEventListener("unhandledrejection", onUnhandledRejection);
try {
const loadingTask = getDocument(basicApiGetDocumentParams);
loadingTask.onProgress = onProgress;
await waitForProgress;
await loadingTask.destroy();
// There's probably a better way to wait a bit.
await sleep(1000);
} finally {
window.removeEventListener("unhandledrejection", onUnhandledRejection);
}
});However, it still doesn’t work because triggering this error requires very specific timing. For example, I created a simple reproduction by modifying this file, and I can only get this error when throttling is enabled (probably because the PDF is too small). So i think it won't be possible to write a reliable test. Code<!doctype html>
<html>
<head>
<meta charset="UTF-8" />
<title>'Hello, world!' example</title>
</head>
<body>
<h1>'Hello, world!' example</h1>
<button id="reload">Reload</button>
<br /><br />
<canvas id="the-canvas" style="border: 1px solid black; direction: ltr"></canvas>
<script src="../../build/generic/build/pdf.mjs" type="module"></script>
<script id="script" type="module">
pdfjsLib.GlobalWorkerOptions.workerSrc = "../../build/generic/build/pdf.worker.mjs";
const url = "./helloworld.pdf";
const canvas = document.getElementById("the-canvas");
const ctx = canvas.getContext("2d");
let loadingTask = null;
async function loadDocument() {
if (loadingTask) {
await loadingTask.destroy();
loadingTask = null;
}
loadingTask = pdfjsLib.getDocument({url});
try {
const pdf = await loadingTask.promise;
const page = await pdf.getPage(1);
const scale = 1.5;
const viewport = page.getViewport({ scale });
const dpr = window.devicePixelRatio || 1;
canvas.width = viewport.width * dpr;
canvas.height = viewport.height * dpr;
canvas.style.width = viewport.width + "px";
canvas.style.height = viewport.height + "px";
const transform = dpr !== 1 ? [dpr, 0, 0, dpr, 0, 0] : null;
page.render({
canvasContext: ctx,
viewport,
transform,
}).promise;
} catch (err) {
if (loadingTask?.destroyed) return;
console.error(err);
}
}
// initial load
loadDocument();
document.getElementById("reload").onclick = loadDocument;
</script>
<hr />
<h2>JavaScript code:</h2>
<pre id="code"></pre>
<script>
document.getElementById("code").textContent =
document.getElementById("script").text;
</script>
</body>
</html>Screen.Recording.2026-01-09.at.21.35.16.mov |
Contributor
|
I think it should be good. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Fixes #11595, where cancelling loading with
loadingTask.destroy()before it finishes throws aWorker was terminatederror that CANNOT be caught.When worker is terminated, an error is thrown here:
pdf.js/src/core/worker.js
Line 374 in 6c74626
Then
onFailureruns, in which we throw again viaensureNotTerminated(). However, this second error is never caught (and cannot be), resulting in console spam.There is no need to throw any additional errors since the termination is already reported here, and
onFailureis supposed to handle errors, not throw them.