On Mon, Mar 11, 2019 at 11:35 AM Dave Townsend <dtowns...@mozilla.com> wrote:
> Woah this email got long. How Firefox considers whether to pass off to an > existing instance of Firefox or continue launching a new one turns out to > be more complex than you might expect. I'm mostly interested in making > folks aware of and giving feedback on how this works after I've changed > some things so feel free to jump down there. But I figured some folks might > find some context in how things work currently. For that, read on! > > One of the goals of pushing to a profile-per-install model for Firefox is > allowing users to run different versions of Firefox side-by-side without > the additional hassle of editing shortcut files or running from the command > line. This has meant changing the "remoting" code, which searches for > existing instances of Firefox and passes command line arguments to them > instead of starting up normally. I landed the changes to this a couple of > days ago and I thought it was worthwhile explaining what has changed since > it might not be exactly what you expect. And if that is the case figure out > whether it makes sense to make any changes. > > *So first, a quick recap of what remoting has done in the past, because it > varies from platform to platform...* > > OSX is the easy case. Firefox doesn't handle remoting at all. OSX does it > all, assuming you are running Firefox by running an app bundle or a dock > icon. OSX sees that an existing Firefox is running and just sends it a > message, a new Firefox instance doesn't even start. I've made no changes > here. > > Windows is the slightly more complex case. When run Firefox attempts to > find an already running Firefox. If one exists it passes its command line > off to it and quits. The -no-remote command line argument is a way to > bypass this behaviour, running with it will stop the new Firefox from > attempting to find an existing instance or becoming and instance that can > be found by other instances. Basically there can only be one Firefox open > that can be found by future invocations. The -new-instance command line > argument is parsed on Windows ... and then ignored. > > Finally there is Linux. The more exciting case. Unless -no-remote or > -new-instance are passed on startup linux will search for an existing > version of Firefox based on a few criteria .. which varies a little > depending on whether we're using dbus remoting or X remoting. We use X > remoting if we are using X11 windows, and dbus if not (and dbus is > supported). In both cases on startup Firefox attempts to find an existing > instance of Firefox with the same remoting name (or you can provide a > different remoting name with -a on the command line). dev-edition has one > remoting name, all other versions of firefox have a different one. If there > is more than one .. which one wins seems undefined. You can additionally > pass "-P <profile name>" in which case Firefox will only select an existing > instance running the named profile. On X remoting there are a few extras. > Passing "-a any" on the command line will find any running Firefox > regardless of remoting name. Passing "-u <username>" will consider > Firefoxen run by the given user (otherwise it only looks at those run by > the current user). -no-remote means FIrefox doesn't register itself to be > found by future instances. -no-remote or -new-instance means we don't look > for existing instances on startup. > > So that's all rather complicated. To make matters more fun the linux and > windows implementations are handled by totally separate code running at > different times during startup. The two key problems here were that windows > completely didn't support more than one instance running, unless all but > one were -no-remote, and linux was horribly complex and again unless you > ran with command line arguments didn't support more than one Firefox at a > time. We wanted something that allowed running Firefox release and Firefox > beta and Firefox nightly with no special arguments at the same time. > > So I have done three things. Removed support for some of the things Linux > supported. Made the code a lot more shared between windows and linux so > things happen at the same time regardless of platform and both platform > have what should be identical behaviours. Changed the order of when some > things happen. > > What did I remove? Support for remoting to a different remoting name and a > different user. Both seem unlikely to be useful for normal use cases, the > latter frankly feels like a security risk. > > *How does it all work now?* > > OSX hasn't changed, maybe we'll want to do some changes here, but for now > it already allows running different versions of Firefox so long as they are > using different profiles, which is the default. So for the rest of this > assume I'm talking about Linux (dbus or x11) and Windows. They all should > behave the same. > > The new remoting does everything based on profile. When starting Firefox we > do normal profile selection, which includes considering any -P and > --profile command line arguments. Once we've selected a profile we attempt > to find an existing Firefox instance using that profile. If one is found we > send it our command line arguments and quit. If not continue start up. > Since different installs of Firefox use different profiles by default this > generally means that running Beta would pass off to an existing Beta. Same > for other installs. It also means if you do "firefox -P foo -url > www.google.com" we'll open that url in profile Foo, either by using an > existing Firefox using profile Foo or by starting with profile Foo. > > -no-remote and -new-instance still exist. Right now they do the same thing, > they make Firefox not look for existing instances and not listen for > remoting from future instances. They are pretty pointless now though, the > only case where they would have an effect is when a second instance is > trying to use a profile that is already used by an existing instance ... at > which point we'll show the profile locked dialog on startup and refuse to > startup anyway. > > The most visible side-effect that folks have started seeing from this > change is caused by waiting for profile selection to occur before > attempting to remote. If Firefox is configured to always show the profile > manager on startup then attempts to open links from outside apps will cause > the profile manager to show, because that is what selects the profile. > Selecting the profile of an already running Firefox from the UI will then > remote to that Firefox (barring a bug that should be fixed in the next > nightly), but this is a change in behaviour and honestly not one I'd > spotted before landing. In some ways the new behaviour kinda makes sense > (if there wasn't already a Firefox running you'd get the profile UI > previously too) but I can see how it is confusing too so it might be worth > considering changing something here, we'd just have to figure out what > profile we should use in this case. > > The other thing that might be confusing is that the version or install of > Firefox you try to launch doesn't affect which version or install of > Firefox you might end up remoting to. This has always been the case on > Windows and normally the case on Linux, unless you pass an extra command > line argument though so I'm not too concerned here. > > Hopefully this all makes sense. I'd like to hear if folks think that this > is the wrong way to support this and if you spot any issues with it that I > haven't. > _______________________________________________ > dev-platform mailing list > dev-platform@lists.mozilla.org > https://lists.mozilla.org/listinfo/dev-platform > _______________________________________________ dev-platform mailing list dev-platform@lists.mozilla.org https://lists.mozilla.org/listinfo/dev-platform
