Do we have any agenda for extensions? I'm using FireGestures and it's
broken since this has landed, just shouting out a lot of "unsafe CPOW
usage" (missing the "forbidden" tho).
Is the action here limited to just file a bug on the add-on side to fix
this or can we do anything on our side? (I presume and also support
that add-ons should be fixed here.)
Thanks.
-hb-
On 1/27/2016 17:42, Mike Conley wrote:
The spaghetti was put in the machine last night - this work has now
landed on mozilla-central.
If you start seeing "unsafe CPOW usage forbidden" in the Browser Console
for various things, please mark them blocking bug 1233497.
Thanks all,
-Mike
On 20/01/2016 3:54 PM, Mike Conley wrote:
(cross-posted to both dev-platform and firefox-dev)
*
*
TL;DR: Shortly, I’ll be flipping a pref to outlaw unsafe CPOWs in almost
all browser code. Unsafe CPOWs inside add-on scopes should continue to
work properly. If you start seeing "unsafe CPOW usage forbidden” errors
being throw for a feature you’re working on in the Browser Console, it’s
because unsafe CPOWs have been outlawed and you should stop using them.
Talk to me if you run into problems.
Details:
“unsafe” CPOWs[1][2] are CPOWs that are accessed when the other process
is not currently blocked waiting for information from you. For example,
if you access gBrowser.selectedBrowser.contentDocumentAsCPOW.body when
the content process is garbage collecting, the parent will be blocked
until the child decides that it has a moment to service the synchronous
message and return the information that the parent needs. Unsafe CPOWS
are generally pretty horrible for performance, especially because we
cannot know what state the other process is in.
“safe” CPOWs are when the other process is in a known blocked state -
for example, the content process sends a synchronous message to the
parent asking for some information, and is blocked waiting for a
response. The parent then accesses CPOWs in the content process safely,
because the content process is in a known state. The only overhead here
is the IPC traffic.
“unsafe” CPOWs are often used by add-ons to synchronously manipulate
content. A year or so back, a bunch of browser code also used unsafe
CPOWs in this way, but we’ve been slowly but surely weeding them out.
We’re at the state now where we believe we’ve eliminated most of the
in-browser unsafe CPOW uses[3].
Within the next day or so, I’m going to be landing bug 1233497[4] which
will cause unsafe CPOW usage in non-addon browser code to throw. In the
event that this breaks things horribly, there is a pref[5] that we can
flip to turn unsafe CPOWs back on while we fix things.
Again, this work is occurring in bug 1233497[4]. If there are any major
concerns, please bring them up here before I throw the spaghetti into
the machine.
For more details on unsafe CPOWs, please read [1] and/or [2].
[1]:
https://mikeconley.ca/blog/2015/02/17/on-unsafe-cpow-usage-in-firefox-desktop-and-why-is-my-nightly-so-sluggish-with-e10s-enabled/
[2]: http://blog.lassey.us/2015/01/10/unsafe-cpow-usage/
[3]: Outside of tests, and a few other little things that there are
follow-ups for.
[4]: https://bugzilla.mozilla.org/show_bug.cgi?id=1233497
[5]: dom.ipc.cpows.forbid-unsafe-from-browser
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