283374 - nsMsgWindow and nsMsgProgress leak due to cycle

Status: VERIFIED FIXED

(Thunderbird :: Message Compose Window, defect)

Description

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

nsMsgWindow and nsMsgProgress leak since each one owns the other and nothing
breaks the cycle.

Steps to reproduce (using trace-refcnt or your favorite leak instrumentation):
 * start thunderbird
 * press Ctrl-M
 * type an email address, TAB, a subject ("test"), TAB, a message ("test")
 * click the X in the corner of the window
 * choose "Save" (to Drafts)
 * quit thunderbird

This is responsible for an increase of 1 in the ++DOMWINDOW / --DOMWINDOW count
since nsMsgProgress owns a JS object (which keeps the window object for the
compose window alive), due to the code here:
http://bonsai.mozilla.org/cvsblame.cgi?file=mozilla/mail/components/compose/content/MsgComposeCommands.js&rev=1.61&mark=1848#1835

Comment 1

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Attachment: stack showing nsMsgWindow held by nsMsgProgress

Comment 2

[David Baron :dbaron: (⌚️UTC-4, no longer working on Mozilla)]

Attachment: stack showing nsMsgProgress held by nsMsgWindow

Comment 3

[(not reading, please use [e-mail] instead)]

re-assign to mscott

Comment 4

[(not reading, please use [e-mail] instead)]

oops, this might be seamonkey bug, and not tbird.  (but tbird may have this
problem, too.)

Comment 5

[Scott MacGregor]

Attachment: the fix

good find dbaron.

I could have easily broken the cycle by calling
m_msgWindow->SetStatusFeedback(nsnull) after we issue the on stop notification 


However, I don't believe the progress class should have a strong reference to
the msg window anyway, so instead I re-wrote it to use a weak reference.

Now the progress object gets destroyed after the msg window is released
(usually on shut down). 

In addition to the weak reference change, we could also clear out the status
feedback reference by hand after the progress class issues an on stop
notification. That would cause the progress object to get deleted right away
instead of waiting until the msg window goes away or someone else sets a status
feedback object on the msg window.