(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 _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
