Dev Connection

Ed Burnette

How MonoTouch gets around Apple's VM restrictions

By Ed Burnette | February 18, 2010, 11:16am PST

Summary: You’ve probably heard that Apple does not allow any interpreted or run-time compiled programs on the iPhone. That’s why you don’t see Flash, C#, or Java programs there. Now, companies like Adobe and Novell are trying to do something about that. In a ZDNet Q&A, Joseph Hill, product manager for Mono at Novell explains their approach with MonoTouch.

You’ve probably heard that Apple does not allow any interpreted or run-time compiled programs on the iPhone. That’s why you don’t see Flash, C#, or Java used on the iPhone. Now, companies like Adobe and Novell are trying to do something about that. In a ZDNet Q&A, Joseph Hill, product manager for Mono at Novell explains their approach with MonoTouch.

The MonoTouch project lets you run Mono programs on the iPhone. Mono is an open source implementation of Microsoft’s .NET platform sponsored by Novell. Normally, .NET code written, for example, in C# runs inside of a virtual machine. The VM takes an intermediate form of the code called bytecode (or in the case of .NET, MSIL) and either interprets it or does a Just-In-Time compilation to native code as needed. Apple doesn’t allow that, so as Joseph Hill explains, Novell had to take a different tack.

Ed: Why does Apple allow .NET development with MonoTouch when they don’t allow Java development on the iPhone/iPad?
Joseph: Java (and other runtimes) are restricted from being deployed to the iPhone because an application cannot execute writable memory. Virtual machines like Java and .NET generate native code from bytecode at runtime, and then execute this code; however, for various reasons, the iPhone kernel will not allow this code to be executed. Mono’s Ahead-Of-Time (AOT) feature avoids this issue by generating all native code that the application could generate at runtime ahead-of-time, so the application deployed to the iPhone is a 100% native application.

Ed: Does Ahead-Of-Time compilation make some features of .NET unavailable?
Joseph: The primary feature that is lost to AOT compilation is Reflection.Emit. (Since this would generate code that could not be executed.) Normal reflection is okay.

Next: Do I still need a Mac? >

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Topics

Apple iPhone, Mono, Developer, Apple Inc., Tool, MonoTouch, VM, Ed, Joseph, MonoDevelop, Objective-C, .Net, C#, Development Tools, Open Source, Software Development, Software/Web Development, Programming Languages, Ed Burnette

Ed Burnette is a software industry veteran with more than 25 years of experience as a programmer, author, and speaker. He has written numerous technical articles and books, most recently "Hello, Android: Introducing Google's Mobile Development Platform" from the Pragmatic Programmers.

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RE: How MonoTouch gets around Apple's VM restrictions

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mono iPhone = icrap

Linux Geek 18th Feb 2010

combine 2 proprietary technologies from monopolists like M$ & Apple and end up with a mess.

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Your parents must have been monopolists

markbn 18th Feb 2010

on something, cause they produced you: a mess

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You're wrong on Mono

nDuDut 18th Feb 2010

Mono is open source, and is sponsored by Novell.

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Yup - it HAS to be licensed that way

imric_z 19th Feb 2010

and written by those who truly believe that Microsoft's short-term limited covenant not to sue certain distributors means it is A-OK - IF you want to succeed at "poisoning the well" of free software, that is... J/K, Microsoft is all about giving competitors a leg up, and all about ameliorating any negative effect it's monopoly may have on the market...

Go, team Miguel.

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RE: How MonoTouch gets around Apple's VM restrictions

curtis.wensley 18th Feb 2010

I love what they're doing with mono, and this is the perfect
approach - bring .NET to platforms that MS wouldn't even
consider. This is a HUGE advantage to corporations that
can make use of existing resources and code.

With Win Phone 7 coming, which most likely will be
(mostly?) developed in .NET, this will give a way to share
development across many devices (considering mono is
now coming to android as well!).

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Mono supports multi-task

LBiege 18th Feb 2010

So how does it fit in a non-multitask iPhone?

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Maybe you get multiple Mono tasks inside a single iPhone task?

Robert Carnegie 2009 19th Feb 2010

Is one way.

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The iPhone multitasks quite well.

Ralfthedog 22nd Feb 2010

You can run as many threads on an iPhone application as the hardware can support. The multitasking restriction on the iPhone is related to outside events and applications.

Apple does not want a large number of applications running in the background. This eats up batteries fast. Thus, when the phone rings or another event interrupts the game you are playing, your applications is suspended. When your phone call is over, the application is restored.

Some Apple applications and processes are allowed to multitask. If you are playing a game or looking at a map, you phone can ring.

Application designers can create simulated multitasking applications with notifications. Lets say one of the users of your weather program is about to be run over by a tornado. You send a trigger to Apples notification server. The server tells your users phone to wake up the weather program and post a message. The weather program tells your user to duck and cover.

From the programmers perspective, the only limitation is that your program can't run when another program is running. From the users perspective, he does not lose the game because of an incoming phone call and his batteries last 10 times longer.

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Contributr

Multiple threads in the foreground are ok

Ed Burnette 1st Mar 2010

Apple allows as many tasks (threads) in the foreground application as you want. In fact it's a necessity if your program is doing any network I/O or other long-running code so that your user interface doesn't get locked up.

What they don't allow is programs running in the background. Unless you're a special blessed Apple-written app like the music player or phone, as another poster noted.

Android allows background processing, but programmers have to be really careful not to overuse it, or it will drain the battery. That's why when the battery runs down and you get that "please charge your phone" message, there's a button at the bottom that will open up a list of the top applications that used the battery. If you spot a battery hog on the list you can uninstall that program and get another one that works better. Or not. It's entirely up to you.

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RE: How MonoTouch gets around Apple's VM restrictions

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RE: How MonoTouch gets around Apple's VM restrictions

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