951805 - Alert does not block UI thread execution

Status: UNCONFIRMED

(Core :: DOM: Core & HTML, defect, P5)

Description

[droberge]

Attachment: multi-alert.html

User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.63 Safari/537.36

Steps to reproduce:

1. Create global variable, e.g. var tmp = 1
2. Create, open and send an XHR with a onreadystatechange handler that modifies the global variable when the readyState equals 4. Assume the XHR takes some time to complete (e.g. 3 seconds)
3. While the XHR is in progress, display an alert dialog
4. Leave dialog open until XHR completes
5. Close dialog, and open another alert dialog with the global variable value


Actual results:

The global variable is modified between the first alert showing and the second alert showing. It's as if the onreadystatechange handler is executed concurrently on the UI thread while the alert is showing


Expected results:

I feel the onreadystatechange handler should not be executed until the current javascript execution completes, e.g. both alerts are displayed and closed.

Comment 1

[droberge]

Attachment: slow-server.py

Comment 2

[droberge]

Attachment: multi-alert.html

Comment 3

[Olli Pettay [:smaug][[e-mail]]]

Dup of some old bug. Alert runs in the same thread as the page. 
Multiprocess FF will help here.

Comment 4

[Firefox Bug Husbandry Bot]

https://bugzilla.mozilla.org/show_bug.cgi?id=1472046

Move all DOM bugs that haven't been updated in more than 3 years and has no one currently assigned to P5.

If you have questions, please contact :mdaly.