[groby_b]

Sure. If you're willing to log out of your smart phone context, and restart any needed tools in the new guest context whenever you hand over your phone.

Oh, I'm sorry, you wanted instantaneous user switching? That's a smidgen harder than the 40-year-old solutions :)

[masklinn]

> Oh, I'm sorry, you wanted instantaneous user switching? That's a smidgen harder than the 40-year-old solutions :)

These OS have been able to run multiple concurrent user sessions for 40 years, and fast user switching has been a feature of all desktop OS since Windows 9x went the way of the dodo.

There are specific issues (core services of these systems are probably — sadly — coded with the idea that a single user is running), but nothing which should be hard to fix.

[groby_b]

The biggest issue is resource limitations - multi-user systems require an abundance of resources that phones don't have.

What about the memory overhead of concurrent sessions?

Who gets to run background processes, and when are they terminated? Because neither CPU nor battery life exist in abundance.

What happens to incoming calls/e-mails/texts/notifications? (Especially for the guest account, where you don't have a second phone number for that account)

What happens to e.g. alarms set by user1 if user2 is logged in?

Which settings are shared, which aren't? And if your phone storage is encrypted, how do you handle shared settings? What about privacy? Can user1 e.g. record GPS signals even if user2 is logged in? If not, what about "Find my phone" features?

Sure, conceptually it's a solved issue. Practically, there are innumerable details to be figured out.

[pyre]

I thought that iOS and/or Android gave each App its own user account in order to sandbox permissions between apps, so that they can't overwrite each other's files. If all of the user data for an app is owned by that app's uid, then wouldn't this allow someone else running that app to somehow gain access to user data from another 'actual' user?

E.g.

App1 has uid 100 User1 has uid 101 User2 has uid 102

If all userdata for App1 is owned by uid 100, User1 or User2 could potentially used App1 to gain access to the other user's app-specific user data.

(I'll admit that I'm not an iOS or Android programmer, so I may be a bit out of my depth here.)

[pyre]

This is a good example of how HN has gone down the tubes. I've been downvoted to -1 based solely on a post where I raised a possible security concern. I admitted that I wasn't fully versed, but I expected someone to correct my if I was wrong. Instead, I'm downvoted, but no one has bothered to actually post useful information. Am I wrong? Did someone just 'not like the tone' of my post for some strange reason? Who knows? No one is talking.

[Dylan16807]

Ephemeral voting noise is not going down the tubes.

[rlpb]

You are right, and I upvoted you.

On Android, uids are used for apps, not for users. Supporting multiple users on Android is thus not as simple as one might think.

[pygorex]

You mean Fast user switching? http://en.wikipedia.org/wiki/Fast_user_switching

[groby_b]

I mean fast user switching on a resource-constrained portable device. There's a bit of a difference in terms of how to do it. (See also my above post listing some of the issues)

[zokier]

Current gen mobile phones are already more powerful than my first Windows XP desktop. I don't think computing resources are a limiting factor here.

[groby_b]

And your XP desktop actually worked well with fast user switching? On an XP minspec machine? Or even recommended specs? There was a reason it was Powertoys only.

Not to mention that your XP machine had a HDD as a backing store for virtual memory. You could safely page out an entire session. Not so for phone OS's, AFAIK. (I know iOS doesn't have a backing store. Haven't checked Android, but I seriously doubt it)

Not to mention we've only very recently reached specs that make this doable. The iPhone 3GS (not that old) did have a 600MHz processor and 256MB of RAM. That's pretty close to an XP recommended spec, IIRC.

Given that your XP machine wasn't running on a battery, and wasn't busy in the background doing phone-y things, you can see where resources are getting tight.

Phones are just getting there, spec-wise. I'm sure sooner or later we will see a guest mode. The 'when', IMHO, hinges more on solving the UX issues, since specs always march on.