PDFPageProxy.prototype.render().promise resolves even after being canceled.

Attach (recommended) or Link to PDF file here: N/A

Configuration:

• Web browser and its version: Brave 1.14.81
• Operating system and its version: Ubuntu 18.04.5
• PDF.js version: 2.6.347
• Is a browser extension: nope

Steps to reproduce the problem:

1. call PDFPageProxy.prototype.render()
2. call renderTask.cancel() before the task

What is the expected behavior? renderTask.promise should not resolve. I’d expect that the promise resolving to indicate that rendering is complete. It instead means that rendering is either complete or canceled.

What went wrong? renderTask.promise does resolve after calling renderTask.cancel(). It’s really nice that there is a cancel method though. Thanks for that and this project generally. It will greatly increase the value proposition of my own products.

[Snuffleupagus]

That’s exactly my use-case. My abstraction over the viewport scaling (i.e. zoom) called the render method and called cancel at the wrong time.

You may perhaps find the viewer components examples helpful, see https://github.com/mozilla/pdf.js/tree/master/examples/components, since they provide a higher-level abstraction compared to using the API directly; see e.g. the simpleviewer example there or perhaps also the mobile-viewer example.

Note that those examples are using the same components that are also used to build the full demo viewer: https://github.com/mozilla/pdf.js#online-demo

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Finally, as already mentioned, it’s unfortunately going to be difficult for anyone to provide further assistance without a runnable example here.

[Snuffleupagus]

renderTask.promise should not resolve.

Note that as mentioned in the JSDocs, it’s actually rejected when rendering is cancelled; see https://github.com/mozilla/pdf.js/blob/d49b2f6cc2b7ed86da22d55ddb1af0b8a5fe5a1e/src/display/api.js#L2753-L2758 Furthermore, there’s also unit-tests that enforce this behaviour; see https://github.com/mozilla/pdf.js/blob/d49b2f6cc2b7ed86da22d55ddb1af0b8a5fe5a1e/test/unit/api_spec.js#L1766-L1789

Hence it’s quite possible that you’re simply running into the following situation: If the task is currently rendering it will not be cancelled until graphics pauses with a timeout., given that rendering may actually finish before it has a chance to get cancelled.

If the above isn’t sufficient to address this issue, please see https://github.com/mozilla/pdf.js/blob/master/.github/CONTRIBUTING.md (emphasis mine):

If you are developing a custom solution, first check the examples at https://github.com/mozilla/pdf.js#learning and search existing issues. If this does not help, please prepare a short well-documented example that demonstrates the problem and make it accessible online on your website, JS Bin, GitHub, etc. before opening a new issue or contacting us in the Matrix room – keep in mind that just code snippets won’t help us troubleshoot the problem.