8 ms·

Mobile Multitasking

75 points by anderzole 17y ago

wvenable 17y ago
The close button on Windows Mobile never closed the apps either, it just minimized them. If you ran out of memory, Windows Mobile would close the oldest used application automatically. A great blog post, the Emperor has No Close about this: http://blogs.msdn.com/windowsmobile/archive/2006/10/05/The-Emperor-Has-No-Close.aspx http://blogs.msdn.com/windowsmobile/archive/2006/10/05/The-E...
- qeorge 17y ago
  The default is to minimize apps when you tap the close button, but kill them if you hold it down. You can change this in the preferences.
- izendejas 17y ago
  If anyone still uses Windows Mobile, I recommend WkTask (not sure it works on 6.5): http://soft.photoracer.net/docs/wktask_en.html http://soft.photoracer.net/docs/wktask_en.html Map a key to launch it. Hit down, then hit close and voila. Can also switch quickly between open apps. I'm planning to get an android device, but was very disappointed when I played with a droid and learned you can't always kill apps. The culprit in this case was the fandango app. Even after an update, I had to uninstall it because it wasn't responding. Maybe I don't know how to use the app manager?
mrshoe 17y ago
I'm glad that iPhone OS is providing us an excuse to take personal computing a least a few steps down the path to where it should have gone years ago. Users shouldn't have to launch and quit applications. They shouldn't have to save and open documents. State should just persist. Always. If you pull the plug on your box you should be able to plug it back in and all state should be restored within seconds. All applications should always be "running" and in the same state you last left them. You only need to switch focus between them as you perform your tasks. Can modern OSes really not be made smart enough to manage our systems in this way? Why do users decide which applications get memory and CPU resources? Why do I need to manually start a bunch of applications and open documents after restarting my computer? None of this makes sense. Hopefully iPhone OS can push us further down this path.
- alanthonyc 17y ago
  I agree. I was showing my iPad to a friend the other day and she asked me how to save a Pages document. It took me a few seconds to figure out how to explain that there was no need to save documents. Documents are just always there.
- vsync 17y ago
  You mean, following down the path that Palm OS devices used since first released in 1996?
  - Maktab 17y ago
    Or Newton OS devices from 1993. This isn't the first time that Apple has tried to build a computer with seamless state persistence and without a traditional exposed file system. That said, neither Palm OS or Newton OS could multitask. Android and the iPhone OS seem to have found a very elegant approach to that particular problem without compromising the user experience.
    - sanj 17y ago
      Actually, both of them could, but just in very limited ways. The Palm had 4 threads, only one of which was available to the developer. Another was used for comms and a third for graffiti processing. I don't think the last one was allocated. The Newton had at least two threads -- comms in the background were needed even in those dark ages.
- jared314 17y ago
  Task-oriented UI?
- wvenable 17y ago
  If you want to edit a document and then save it as a new document you have to make that choice before you start editing on the iPad. A lot of people are going to destroy a lot of documents that way. It could be a simple fix to still keep the same model but right now it's not very intuitive.
deleted 17y ago
[deleted]
ajg1977 17y ago
I'm curious why iPhone can't page application memory out to persistent storage (whatever of that 16GB etc you're not using for music) when they're in the background and RAM runs low. That would be the ideal - frozen background apps saved to persistent storage until needed without sitting in RAM. I'm assuming the OS is modern enough that all apps have their own address space so perhaps the hardware doesn't have an MMU capable of the necessary remapping of physical memory into a different address space. Oh and two nits with Grubers piece. 1) This system is well thought out but it's hardly "state of the art" and 2) on iPhone OS 4.0 backgrounded apps will receive a willTerminate notification before they're completely terminated.
- wvenable 17y ago
  When an app is swapped to disk, all it's code and data pages are stored. When it's resumed, the code and data pages are loaded back. This isn't so terribly different from relaunching the application (loading the code) and having the app restore it's state (loading the data). In fact, the app can even be more efficient in saving it's own state because it can discard anything it knows it doesn't need. Paging is really only necessary if you can interact with more than one application at time. On an iPhone, that doesn't happen. Paging is probably less efficient than this system.
  - ajg1977 17y ago
    Paging is a technique to free up RAM. Whether its used to enable interaction with multiple apps, to allow a single app access to more memory than physically exists, or to allow more apps to be frozen in the background is irrelevant. It is neither better nor worse than the system Apple has designed. Its just different. And yes, an app can manually attempt to restore it's state but a) doing so can be quite tricky (keyboard up, word half-typed) and b) it's puts a heavy onus on developers, many of whom just do not bother.
    - mattdw 17y ago
      Of course, then you have to deal with resources – like when you unfreeze your app partway through typing a word, but in the meantime the user has changed keyboard layouts, or you unfreeze the camera program but meanwhile something else has been using the camera and left it in a different state. Better to persist as little as you need, and deal with everything else through clearly defined lifecycles, IMO. Although, I also think programming languages should provide immutable datatypes by default ;).
deleted 17y ago
[deleted]
xal 17y ago
I love daringfireball's new tagline.
- mattparcher 17y ago
  "Insightful and Not Negative" (A reference to Steve Job's supposed appraisal of John Gruber's article about the iPhone TOS Section 3.3.1. See: http://news.ycombinator.com/item?id=1255858 http://news.ycombinator.com/item?id=1255858)
TimothyFitz 17y ago
What's the link between blocks/grand central and multitasking on the iPhone?
- allenbrunson 17y ago
  none. grand central is a scheme to make it easier to parallelize your code, generally so it can take advantage of two or more cpu cores. not much use on iphone devices, which aren't going to have more than one core for a long time. blocks add closure-like abilities to C. multitasking, in this context, is a way to run two or more third-party apps at once. so, basically, no overlap at all.
  - brisance 17y ago
    Apple may be laying the groundwork for specialized multicore processors on mobile handsets. Take the just-released Macbook Pros for example. nVidia's Optimus has controls at the application-level whereas Apple's technology is at the library/framework-level. There is no user interaction to switch between different graphics chipsets; depending on need for performance/battery life, the OS does "the right thing". Ars has an article on it http://arstechnica.com/apple/news/2010/04/inside-apples-automatic-gpu-switching.ars http://arstechnica.com/apple/news/2010/04/inside-apples-auto...
- mattdw 17y ago
  It sounds like Grand Central is the mechanism through which multitasking roles are described/created; i.e. programmers declare the background parts of their app as closures (GCD blocks) which are handed off to a task manager. I might be wrong on this.
pkulak 17y ago
I'm glad he made this point, but he's still not giving Android enough credit. With Android, apps can create a service that can run and do whatever it likes. It's not limited to a couple APIs. People are pretty jazzed about Skype running in the background, but they are going to be dissapointed when they realize that only means that you can keep the current call running while you leave the app. Skype still won't be able to stay open and listen for incoming calls. Same with chat or IRC apps.
- cpr 17y ago
  Your last paragraph isn't true about VOIP apps, but I can't say more due to the NDA.
  - Zak 17y ago
    I really don't understand why Apple has an NDA on its essentially public developer program. There are so many iPhone developers that all the standard rules and agreements will be made public almost instantly no matter what.
    - wallflower 17y ago
      No, part of the privilege of being a registered iPhone developer is you get access to beta SDKs and information that the public does not. The idea is to give iPhone developers who are in their program a head start. The fear of getting booted from Apple's program is usually sufficient to bite your tongue before you saying something in public that should not be discussed. As an example: now that the iPad SDK is no longer under NDA: one of the most interesting APIs in iPhone OS 3.2 (iPad) is MPMoviePlayerController gaining the backgroundView and view properties. Basically, it opened up a whole arena of interactive video applications that overlay graphics on top of live or recorded video (think watching baseball game on iPad and pulling up player's on-base stats by clicking on magic button hovering near base, true interactive TV, interactive remote control with show previews...) http://developer.apple.com/iphone/library/documentation/MediaPlayer/Reference/MPMoviePlayerController_Class/MPMoviePlayerController/MPMoviePlayerController.html http://developer.apple.com/iphone/library/documentation/Medi...
jsz0 17y ago
You certainly do need a task manager on Android for the simple reason that certain types of applications can be battery hogs. They may not tax the performance of the device enough to be killed automatically. I know Android 2.x is supposed to monitor battery usage but it simply doesn't work very well -- or at all in some cases. Subsonic (streaming audio client) kills my phone's battery if I don't kill it manually with a task manager. The app does not include a quit option. It can kill my battery in about 3 hours even if I pause playback because it keeps its connection to the server open. Another app I use, Jabiru (jabber client), does the same thing but it does have a disconnect and quit option so I wouldn't need a third party task manager to deal with it. So it seems to me Android's multi-tasking is largely dependent on the applications you use.
- Tichy 17y ago
  I admit that in the beginning it is a bit unnerving not to be sure what the apps are doing under the hood. My response to suspicious activity is usually to uninstall the app, though. Some better monitoring device would be useful, but already you can see which services are running, and what has been using the battery. So culprits should be easy to identify and remove, without a task manager.
  - iron_ball 17y ago
    Android gives you a readout of which apps have been using the battery.
    - Tichy 17y ago
      Yes that is what I meant, should have formulated it better.
- notauser 17y ago
  There are two kinds of background processes in Android (unless it's changed since I last wrote an app, which is possible - that was for OS 1.5). This article is describing how the main app (the bit you see) functions. When it is swapped out you get an event, then again if they are killed. The OS manages that. However you can also write services/daemons which are persistent and (as far as I know) not suspended by the operating system. I don't believe they can present a UI but they can communicate with your main app. These are intended for things like occasional server polling and pushing notifications to the bar. But I don't believe there is any technical restriction on using them for other things.
jiri 17y ago
These Android/iPhone apps architecture is very close to web page approach. In web environment, you can load the page, interact with page, you can close it anytime a do something else. Traditional application were different but these modern mobile apps do the same - you open app like page, you navigate somewhere else and OS close app automatically. Some apps are using cloud data but some can use local storage. Its so close to web architecture, that we can see Chrome browser on the other side - it's architecture is making step towards applications by using processes for loaded web pages. Both architectures are closing - apps are more like web pages and web pages are more like apps ...
johnrob 17y ago
Moore's law seems to be in full effect for handsets. I think a lot of the innovation here is a stop gap measure before these handsets have virtual memory, making the complication behind multi tasking obsolete. On a side note, I seem to take heat every time I imply that phones will end up on par with PCs. The common theme I've been pushing is that most of the developments we've seen in PCs over the past decade will reoccur for phones. Is this really so far fetched?
- sunchild 17y ago
  It gets a little silly to talk about "phones" in this context. Making and receiving one-to-one voice communications is already just one of many features, and arguably already not the main feature.
  - comex 17y ago
    And, on the iPad, not a feature at all. :)
- comex 17y ago
  I hope not. My iPad with 256MB of RAM and a relatively slow ARM processor feels snappier than my laptop with 2GB and a dual-core 64-bit Intel processor, partly due to the consistency: I never know, on the latter, whether an application will respond quickly (because it is active in memory), or slowly (because it isn't). If I could use iPhone OS's model on my laptop-- with more freedom due to the increased memory, but still omitting swap in favor of automatic saving/memory management-- I would. though, who knows, maybe the declining cost of RAM will solve this problem for PCs, and eventually phones.
mattparcher 17y ago
His closing thought on the matter: "You know what iPhone OS is missing that Mac OS X has? The SPOD." ("Spinning pinwheel of death", "rainbow beachball of death", etc.: http://en.wikipedia.org/wiki/Spinning_wait_cursor http://en.wikipedia.org/wiki/Spinning_wait_cursor) I'm nearly ashamed to admit I have never noticed it's absence until now.
- bruceboughton 17y ago
  It doesn't have the SPOD, but it does occasionally freeze with an app in an unusable state. The SPOD is only not there because they didn't add it, not because an unresponsive system is impossible with the iPhone OS.
  - ZeroGravitas 17y ago
    SPOD doesn't mean an unresponsive system, just an unresponsive app so this a functional regression in iPhone if you can't switch to other apps while the frozen one recovers.
    - comex 17y ago
      But sometimes it does mean an unresponsive system. All an application has to do is allocate a bunch of RAM (or spin the CPU on a number of threads >= cores) and the system slows to a crawl. It can't really kill those apps unless I ask it to, because work might be lost. On iPhone, if apps save as they go, excessive usage can be solved with a kill -9 when I press the home button. Relaunching the app will take a few seconds and is transparent; I don't have to fight with the malfunctioning instance.
      - tomica 17y ago
        on osX (or any other OS), if apps save as they go, excessive usage can be solved with a kill -9 whenever the OS likes..
jonhendry 17y ago
It'll be interesting to see if Snow Leopard's NSPurgeableData and related stuff moves to iPhone OS. (I gather Google's phone OS have something similar). That'd let developers have cached data that the OS knows it can blow away safely if memory gets low. The app then just regenerates the cache when necessary. If iPhone OS could look around running processes for purgeable data, it could avoid or postpone killing apps outright. That would only be necessary if purging wasn't sufficient. In fact, this seems a lot more useful on a swap-free phone than on OS X itself.
- antrix 17y ago
  > I gather Google's phone OS have something similar Android apps are written in Java. So the standard approach for doing this is to use Java's weak & soft references which basically tell the GC that, "hey, I've used this memory but if you really need it back, you can have it!". http://developer.android.com/reference/java/lang/ref/SoftReference.html http://developer.android.com/reference/java/lang/ref/SoftRef...
  - jon_hendry 17y ago
    Android also has the MemoryFile class, which can be set "purgeable". "MemoryFile is a wrapper for the Linux ashmem driver. MemoryFiles are backed by shared memory, which can be optionally set to be purgeable. Purgeable files may have their contents reclaimed by the kernel in low memory conditions (only if allowPurging is set to true). After a file is purged, attempts to read or write the file will cause an IOException to be thrown."

75 points by anderzole 17y ago

The close button on Windows Mobile never closed the apps either, it just minimized them. If you ran out of memory, Windows Mobile would close the oldest used application automatically. A great blog post, the Emperor has No Close about this: http://blogs.msdn.com/windowsmobile/archive/2006/10/05/The-Emperor-Has-No-Close.aspx http://blogs.msdn.com/windowsmobile/archive/2006/10/05/The-E...

qeorge 17y ago
The default is to minimize apps when you tap the close button, but kill them if you hold it down. You can change this in the preferences.
izendejas 17y ago
If anyone still uses Windows Mobile, I recommend WkTask (not sure it works on 6.5): http://soft.photoracer.net/docs/wktask_en.html http://soft.photoracer.net/docs/wktask_en.html Map a key to launch it. Hit down, then hit close and voila. Can also switch quickly between open apps. I'm planning to get an android device, but was very disappointed when I played with a droid and learned you can't always kill apps. The culprit in this case was the fandango app. Even after an update, I had to uninstall it because it wasn't responding. Maybe I don't know how to use the app manager?

mrshoe 17y ago

I'm glad that iPhone OS is providing us an excuse to take personal computing a least a few steps down the path to where it should have gone years ago. Users shouldn't have to launch and quit applications. They shouldn't have to save and open documents. State should just persist. Always. If you pull the plug on your box you should be able to plug it back in and all state should be restored within seconds. All applications should always be "running" and in the same state you last left them. You only need to switch focus between them as you perform your tasks. Can modern OSes really not be made smart enough to manage our systems in this way? Why do users decide which applications get memory and CPU resources? Why do I need to manually start a bunch of applications and open documents after restarting my computer? None of this makes sense. Hopefully iPhone OS can push us further down this path.

alanthonyc 17y ago
I agree. I was showing my iPad to a friend the other day and she asked me how to save a Pages document. It took me a few seconds to figure out how to explain that there was no need to save documents. Documents are just always there.
vsync 17y ago
You mean, following down the path that Palm OS devices used since first released in 1996?
- Maktab 17y ago
  Or Newton OS devices from 1993. This isn't the first time that Apple has tried to build a computer with seamless state persistence and without a traditional exposed file system. That said, neither Palm OS or Newton OS could multitask. Android and the iPhone OS seem to have found a very elegant approach to that particular problem without compromising the user experience.
  - sanj 17y ago
    Actually, both of them could, but just in very limited ways. The Palm had 4 threads, only one of which was available to the developer. Another was used for comms and a third for graffiti processing. I don't think the last one was allocated. The Newton had at least two threads -- comms in the background were needed even in those dark ages.
jared314 17y ago
Task-oriented UI?
wvenable 17y ago
If you want to edit a document and then save it as a new document you have to make that choice before you start editing on the iPad. A lot of people are going to destroy a lot of documents that way. It could be a simple fix to still keep the same model but right now it's not very intuitive.

deleted 17y ago

[deleted]

ajg1977 17y ago

I'm curious why iPhone can't page application memory out to persistent storage (whatever of that 16GB etc you're not using for music) when they're in the background and RAM runs low. That would be the ideal - frozen background apps saved to persistent storage until needed without sitting in RAM. I'm assuming the OS is modern enough that all apps have their own address space so perhaps the hardware doesn't have an MMU capable of the necessary remapping of physical memory into a different address space. Oh and two nits with Grubers piece. 1) This system is well thought out but it's hardly "state of the art" and 2) on iPhone OS 4.0 backgrounded apps will receive a willTerminate notification before they're completely terminated.

wvenable 17y ago
When an app is swapped to disk, all it's code and data pages are stored. When it's resumed, the code and data pages are loaded back. This isn't so terribly different from relaunching the application (loading the code) and having the app restore it's state (loading the data). In fact, the app can even be more efficient in saving it's own state because it can discard anything it knows it doesn't need. Paging is really only necessary if you can interact with more than one application at time. On an iPhone, that doesn't happen. Paging is probably less efficient than this system.
- ajg1977 17y ago
  Paging is a technique to free up RAM. Whether its used to enable interaction with multiple apps, to allow a single app access to more memory than physically exists, or to allow more apps to be frozen in the background is irrelevant. It is neither better nor worse than the system Apple has designed. Its just different. And yes, an app can manually attempt to restore it's state but a) doing so can be quite tricky (keyboard up, word half-typed) and b) it's puts a heavy onus on developers, many of whom just do not bother.
  - mattdw 17y ago
    Of course, then you have to deal with resources – like when you unfreeze your app partway through typing a word, but in the meantime the user has changed keyboard layouts, or you unfreeze the camera program but meanwhile something else has been using the camera and left it in a different state. Better to persist as little as you need, and deal with everything else through clearly defined lifecycles, IMO. Although, I also think programming languages should provide immutable datatypes by default ;).

deleted 17y ago

[deleted]

xal 17y ago

I love daringfireball's new tagline.

mattparcher 17y ago
"Insightful and Not Negative" (A reference to Steve Job's supposed appraisal of John Gruber's article about the iPhone TOS Section 3.3.1. See: http://news.ycombinator.com/item?id=1255858 http://news.ycombinator.com/item?id=1255858)

TimothyFitz 17y ago

What's the link between blocks/grand central and multitasking on the iPhone?

allenbrunson 17y ago
none. grand central is a scheme to make it easier to parallelize your code, generally so it can take advantage of two or more cpu cores. not much use on iphone devices, which aren't going to have more than one core for a long time. blocks add closure-like abilities to C. multitasking, in this context, is a way to run two or more third-party apps at once. so, basically, no overlap at all.
- brisance 17y ago
  Apple may be laying the groundwork for specialized multicore processors on mobile handsets. Take the just-released Macbook Pros for example. nVidia's Optimus has controls at the application-level whereas Apple's technology is at the library/framework-level. There is no user interaction to switch between different graphics chipsets; depending on need for performance/battery life, the OS does "the right thing". Ars has an article on it http://arstechnica.com/apple/news/2010/04/inside-apples-automatic-gpu-switching.ars http://arstechnica.com/apple/news/2010/04/inside-apples-auto...
mattdw 17y ago
It sounds like Grand Central is the mechanism through which multitasking roles are described/created; i.e. programmers declare the background parts of their app as closures (GCD blocks) which are handed off to a task manager. I might be wrong on this.

pkulak 17y ago

I'm glad he made this point, but he's still not giving Android enough credit. With Android, apps can create a service that can run and do whatever it likes. It's not limited to a couple APIs. People are pretty jazzed about Skype running in the background, but they are going to be dissapointed when they realize that only means that you can keep the current call running while you leave the app. Skype still won't be able to stay open and listen for incoming calls. Same with chat or IRC apps.

cpr 17y ago
Your last paragraph isn't true about VOIP apps, but I can't say more due to the NDA.
- Zak 17y ago
  I really don't understand why Apple has an NDA on its essentially public developer program. There are so many iPhone developers that all the standard rules and agreements will be made public almost instantly no matter what.
  - wallflower 17y ago
    No, part of the privilege of being a registered iPhone developer is you get access to beta SDKs and information that the public does not. The idea is to give iPhone developers who are in their program a head start. The fear of getting booted from Apple's program is usually sufficient to bite your tongue before you saying something in public that should not be discussed. As an example: now that the iPad SDK is no longer under NDA: one of the most interesting APIs in iPhone OS 3.2 (iPad) is MPMoviePlayerController gaining the backgroundView and view properties. Basically, it opened up a whole arena of interactive video applications that overlay graphics on top of live or recorded video (think watching baseball game on iPad and pulling up player's on-base stats by clicking on magic button hovering near base, true interactive TV, interactive remote control with show previews...) http://developer.apple.com/iphone/library/documentation/MediaPlayer/Reference/MPMoviePlayerController_Class/MPMoviePlayerController/MPMoviePlayerController.html http://developer.apple.com/iphone/library/documentation/Medi...

jsz0 17y ago

You certainly do need a task manager on Android for the simple reason that certain types of applications can be battery hogs. They may not tax the performance of the device enough to be killed automatically. I know Android 2.x is supposed to monitor battery usage but it simply doesn't work very well -- or at all in some cases. Subsonic (streaming audio client) kills my phone's battery if I don't kill it manually with a task manager. The app does not include a quit option. It can kill my battery in about 3 hours even if I pause playback because it keeps its connection to the server open. Another app I use, Jabiru (jabber client), does the same thing but it does have a disconnect and quit option so I wouldn't need a third party task manager to deal with it. So it seems to me Android's multi-tasking is largely dependent on the applications you use.

Tichy 17y ago
I admit that in the beginning it is a bit unnerving not to be sure what the apps are doing under the hood. My response to suspicious activity is usually to uninstall the app, though. Some better monitoring device would be useful, but already you can see which services are running, and what has been using the battery. So culprits should be easy to identify and remove, without a task manager.
- iron_ball 17y ago
  Android gives you a readout of which apps have been using the battery.
  - Tichy 17y ago
    Yes that is what I meant, should have formulated it better.
notauser 17y ago
There are two kinds of background processes in Android (unless it's changed since I last wrote an app, which is possible - that was for OS 1.5). This article is describing how the main app (the bit you see) functions. When it is swapped out you get an event, then again if they are killed. The OS manages that. However you can also write services/daemons which are persistent and (as far as I know) not suspended by the operating system. I don't believe they can present a UI but they can communicate with your main app. These are intended for things like occasional server polling and pushing notifications to the bar. But I don't believe there is any technical restriction on using them for other things.

jiri 17y ago

These Android/iPhone apps architecture is very close to web page approach. In web environment, you can load the page, interact with page, you can close it anytime a do something else. Traditional application were different but these modern mobile apps do the same - you open app like page, you navigate somewhere else and OS close app automatically. Some apps are using cloud data but some can use local storage. Its so close to web architecture, that we can see Chrome browser on the other side - it's architecture is making step towards applications by using processes for loaded web pages. Both architectures are closing - apps are more like web pages and web pages are more like apps ...

johnrob 17y ago

Moore's law seems to be in full effect for handsets. I think a lot of the innovation here is a stop gap measure before these handsets have virtual memory, making the complication behind multi tasking obsolete. On a side note, I seem to take heat every time I imply that phones will end up on par with PCs. The common theme I've been pushing is that most of the developments we've seen in PCs over the past decade will reoccur for phones. Is this really so far fetched?

sunchild 17y ago
It gets a little silly to talk about "phones" in this context. Making and receiving one-to-one voice communications is already just one of many features, and arguably already not the main feature.
- comex 17y ago
  And, on the iPad, not a feature at all. :)
comex 17y ago
I hope not. My iPad with 256MB of RAM and a relatively slow ARM processor feels snappier than my laptop with 2GB and a dual-core 64-bit Intel processor, partly due to the consistency: I never know, on the latter, whether an application will respond quickly (because it is active in memory), or slowly (because it isn't). If I could use iPhone OS's model on my laptop-- with more freedom due to the increased memory, but still omitting swap in favor of automatic saving/memory management-- I would. though, who knows, maybe the declining cost of RAM will solve this problem for PCs, and eventually phones.

mattparcher 17y ago

His closing thought on the matter: "You know what iPhone OS is missing that Mac OS X has? The SPOD." ("Spinning pinwheel of death", "rainbow beachball of death", etc.: http://en.wikipedia.org/wiki/Spinning_wait_cursor http://en.wikipedia.org/wiki/Spinning_wait_cursor) I'm nearly ashamed to admit I have never noticed it's absence until now.

bruceboughton 17y ago
It doesn't have the SPOD, but it does occasionally freeze with an app in an unusable state. The SPOD is only not there because they didn't add it, not because an unresponsive system is impossible with the iPhone OS.
- ZeroGravitas 17y ago
  SPOD doesn't mean an unresponsive system, just an unresponsive app so this a functional regression in iPhone if you can't switch to other apps while the frozen one recovers.
  - comex 17y ago
    But sometimes it does mean an unresponsive system. All an application has to do is allocate a bunch of RAM (or spin the CPU on a number of threads >= cores) and the system slows to a crawl. It can't really kill those apps unless I ask it to, because work might be lost. On iPhone, if apps save as they go, excessive usage can be solved with a kill -9 when I press the home button. Relaunching the app will take a few seconds and is transparent; I don't have to fight with the malfunctioning instance.
    - tomica 17y ago
      on osX (or any other OS), if apps save as they go, excessive usage can be solved with a kill -9 whenever the OS likes..

jonhendry 17y ago

It'll be interesting to see if Snow Leopard's NSPurgeableData and related stuff moves to iPhone OS. (I gather Google's phone OS have something similar). That'd let developers have cached data that the OS knows it can blow away safely if memory gets low. The app then just regenerates the cache when necessary. If iPhone OS could look around running processes for purgeable data, it could avoid or postpone killing apps outright. That would only be necessary if purging wasn't sufficient. In fact, this seems a lot more useful on a swap-free phone than on OS X itself.

antrix 17y ago
> I gather Google's phone OS have something similar Android apps are written in Java. So the standard approach for doing this is to use Java's weak & soft references which basically tell the GC that, "hey, I've used this memory but if you really need it back, you can have it!". http://developer.android.com/reference/java/lang/ref/SoftReference.html http://developer.android.com/reference/java/lang/ref/SoftRef...
- jon_hendry 17y ago
  Android also has the MemoryFile class, which can be set "purgeable". "MemoryFile is a wrapper for the Linux ashmem driver. MemoryFiles are backed by shared memory, which can be optionally set to be purgeable. Purgeable files may have their contents reclaimed by the kernel in low memory conditions (only if allowPurging is set to true). After a file is purged, attempts to read or write the file will cause an IOException to be thrown."