1050327 - worker pageshow event fires before the worker's port can send messages

Status: RESOLVED INCOMPLETE

(Add-on SDK Graveyard :: General, defect)

Description

[Alex Prokop]

Attachment: firefox.zip

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_9_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/36.0.1985.125 Safari/537.36

Steps to reproduce:

- add a listener to the 'pageshow' event of the worker passed into the 'onAttach' callback of a PageMod, store each worker in an array to keep track of multiple pages
- in the pageshow listener try to send a message to the worker's content script via port.emit
- when testing the add-on load a page, navigate to another page and then click back
- the first page loads from the cache, the pageshow event fires and the port.emit is called on the worker

A zip containing full source code for an add on is attached. Remove the setTimeout on line 71 of main.js to see the error.


Actual results:

Triggers the error: 'The page is currently hidden and can no longer be used until it is visible again.'


Expected results:

The page show event should not have fired until the worker is able to send a message to the content script. If a setTimeout of 0 is used before an attempt to send this message, it fires correctly.

Comment 1

[Tomislav Jovanovic :zombie]

Irakli: i misunderstood this part during our triage meeting, i thought he was using `pageshow` events on the tab object..

(In reply to Alex Prokop from comment #0)
> - add a listener to the 'pageshow' event of the worker passed into the
> 'onAttach' callback of a PageMod, store each worker in an array to keep
> track of multiple pages

you are using an internal event of our implementation, which i don't even think is documented anywhere. the problem here is that that same event is used by the SDK code to "unfreeze" the page worker after the tab navigates back to a page from BFCache. 

we can't really guarantee SDK code will run before your code, so that's why this happens. the solution for you is to listen for the `pageshow` event in your content script, and send a message back to your addon code from that event listener. that will guarantee your code will be able to interact with a content worker at that point.

Comment 2

[Irakli Gozalishvili [:irakli] [:gozala] [@gozala]]

Documented or not  pageshow / pagehide events have being added as they were necessary to handle certain use cases by add-on authors. That is in fact why events are emitted on worker instances:

https://github.com/mozilla/addon-sdk/blob/master/lib/sdk/content/worker.js#L216-L228

SDK does not really depends on events dispatched on `worker` instances. I also suspect that this bug is caused by the fact that `model.frozen` is mutated after event is emitted. I believe in the past `emit` was async which is why it was mutation of `model.frozen` after worked.

zombie would you be willing to take this bug ?

Comment 3

[Tomislav Jovanovic :zombie]

subtle event timings/orderings like this are going out the window with e10s and my fix in bug 1058698, so i can take this after that lands..

(though i don't necessarily agree this is P1)

Comment 4

[Firefox Bug Husbandry Bot]

https://bugzilla.mozilla.org/show_bug.cgi?id=1399562