I know the answer (it's 42)

A blog on coding, .NET, .NET Compact Framework and life in general....

  • I know the answer (it's 42)

    Emulator updates for the new Windows Phone Mango tools




    One of the most requested feature for the emulator was support for sensor. Developers were apparently asking their managers for travel budget to go to Hawaii/Europe so that they could test out their location based apps :). Today at MIX11 we announced that GPS sensor support for the emulator will be shipped in the next version of the tools. Some of the features that will be present are

    1. Developers would be able to launch a new tool window from the emulator and in that click on locations on maps to feed that location to apps running in the emulator. This covers building apps like Yelp, Weather app on the device that needs static location information
    2. Have pre-recorded location and able to play that out so that new locations are sent to the phone at a preset rate. This covers building apps like sports tracker, navigation apps.
    3. The app running in the emulator will not need to change in anyway or even know that the data is simulated. It will come over the usual sensor channels and even apps like the built in bing maps app will pick up the fed in data.

    Here’s a short video which I quickly took from the laptop of our PM. Being away from family in Las Vegas was getting me down so he took me to Seattle in a second (or rather simulated it).

    Direct link http://www.youtube.com/watch?v=wt0DdiYqdkk 



    Another new sensor support is the accelerometer. So no more picking up the PC monitor running the emulator and rotating it to see if the emulator gets the movements. There’s going to be a new tool window using which the developer can feed in motion to the apps running in the emulator. Also some pre-canned motions like shake will be present. Here’s another video of that

    Direct link http://www.youtube.com/watch?v=Gc1kuXj7eCE 

  • I know the answer (it's 42)

    Generational GC in Windows Phone Mango



    This is an announcement only post, do subscribe to this blog feed or on to http://twitter.com/abhinaba as I’d be making more detailed posts on how we are building the Generational GC and what developers need to know.

    Today in the MIX11 keynote ScottGu just announced something that I’ve been working on for some time. The next version of the Windows Phone will have a Generational Garbage Collector (GenGC for short). A bunch of folks has worked real hard to get this piece into WP7 in a short time.

    Today on Windows Phone 7 we have a stop the world, mark-sweep-compact, non-generational GC. When it runs it pauses the entire execution, looks through each object in the application to find and eliminate all unused data. This manifests as longer app startup time and stutters during time critical execution.

    In Mango we are adding Generational GC to reduce collection latency to address both of these problems . Existing apps and games even without any changes can expect faster startup, faster level loads and reduction in gameplay stutters due to collection. Developers can specifically optimize for the new generational GC to completely remove stutters during animations and game play that came due to these GC pauses.

    As an example see how one of the existing games butterfly benefits from the GenGC. One of the phone below is running the GenGC and the other is not and it should be obvious which one is based on which starts up first (do note that both in Keynote and here we are showing startup gains because it’s easier to show that. In gameplay stutters is hard to show on lower resolution videos). Also note that not just at the core startup at every level it gets a bit faster.

    Direct link http://www.youtube.com/watch?v=FtusaSuFIpc

    Please refer to my previous blog http://blogs.msdn.com/b/abhinaba/archive/2009/03/02/back-to-basics-generational-garbage-collection.aspx on what is a generational GC and how it helps.

    The new GenGC uses 2 generations and write barriers to track Gen1 to Gen0 references. This post is just to announce the feature. I will be making a series of posts to get into the gory details as we get closer to handing over the bits to our developers. I am sure the developers would want to know the sizes of the various generations, when full vs generational collections happen and so much more. Do register to my blog feed or my twitter account http://twitter.com/abhinaba  for the announcements as I publish these posts.

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    SIMD/ARM-NEON support in Windows Phone Mango


    This is an announcement only post, do subscribe to this blog feed or on to http://twitter.com/abhinaba as I’d be making more detailed posts on these topics as we get close to handing over these bits to our developer customers.

    ARM processors support SIMD (Single Instructions Multiple Data) instructions through the ARM® NEON™technology that is available on ARMV7 ISA. SIMD allows parallelization/HW-acceleration of some operations and hence performance gains. Since the Windows Phone 7 chassis specification requires ARMV7-A; NEON is available by default on all WP7 devices. However, the CLR on Windows Phone 7 (NETCF) did not utilize this hardware functionality and hence it was not available to the managed application developers. We just announced in MIX11 that in the next version of Windows Phone release the NETCF runtime JIT will utilize SIMD capabilities on the phones.

    What it means to the developers

    Certain operations on some XNA types will be accelerated using the NEON/SIMD extensions available on the phone. Examples include operations on Vector2, Vector3, Vector4, Matrix from the Microsoft.Xna.Framework namespace will get this acceleration. NOTE: At the point the exact types and the exact operations on them are not closed yet and subject to change. Do note that user types will not get this acceleration. E.g. if you have rolled out your own vector type and use say dot operations on it, the CLR will not accelerate them. This is a targeted acceleration for some XNA types and not a vectorizing JIT compiler feature.

    Apps and types heavily using these XNA types (our research shows a lot of games do) will see good performance gain. For example we took this Fluid simulation sample from a team (note this was not written specifically for us to demo) and saw huge gains because it heavily uses Matrix and Vector operations to simulate fluid particles and the forces that work in between them. Frame rates shot up from 18fps to 29fps on the very same device.

    Based on the usage of these types and operations in your app you’d see varying amounts of gains. However, this feature should be a good motivation to move to these XNA types.

    How does SIMD work

    SIMD as the name suggests can process the same operation on multiple data in parallel.

    Consider the following Vector addition

    public static Vector2 Add(Vector2 value1, Vector2 value2)
        Vector2 vector;
        vector.X = value1.X + value2.X;
        vector.Y = value1.Y + value2.Y;
        return vector;

    If you see the two lines in blue it’s essentially doing the same addition operation on two data sets and putting the result in two other locations. This today will be performed sequentially. Where the JITer will emit processor instructions to load the X values in registers, add them, store them, and then do the same thing again for the Y values. However, this is inherently parallelizable and the ARM NEON provides an easy way to load such values (vpop, vldr) in single instructions and use a single VADD NEON instruction to add the values in parallel.

    A way to visualize that is as follows


    A single instruction both X1 and Y1 is loaded, another instruction loads both X2, Y2 and the 3rd in parallel adds them together.

    For an easy sample on how that works head onto http://www.arm.com/files/pdf/NEON_Support_in_the_ARM_Compiler.pdf

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    WP7: When does GC Consider a Local Variable as Garbage


    Consider the following code that I received:

    static void Foo()
        TestClass t = new TestClass();
        List<object>l = new List<object>();
        l.Add(t); // Last use of l and t
        WeakReference w = new WeakReference(t);
        Console.WriteLine("Is Alive {0}", w.IsAlive);

    If this code is is run on the desktop it prints Is Alive False. Very similar to the observation made by a developer in http://stackoverflow.com/questions/3161119/does-the-net-garbage-collector-perform-predictive-analysis-of-code. This happens because beyond the last usage of l and t, the desktop GC considers l and t to be garbage and collects it.

    Even though this seems trivial, it isn’t. During JITing of this method the JITer performs code analysis and ensures that runtime tables are updated to reflect whether at a particular time a given local variable is alive or not (it is not used beyond that point). This needs a bunch of data structures to be maintained (lifetime tables) and also dynamic analysis of code.

    In case of Windows Phone 7 (or other platforms using NETCF) for the same code you’d get Is Alive True. Which means the NETCF GC considers the object to be alive even beyond it’s last usage in the function.

    Due to the limited resources available on devices, NETCF does not do these dynamic analysis. So we trade off some runtime performance to ensure faster JITing (and hence application faster startup). All local variables of all functions in the call stacks of the all managed threads in execution during garbage collection is considered live (hence also object roots) and not collect. In NETCF the moment the function Foo returns and the stack is unwound the local objects on it including t and l becomes garbage.

    Do note that both of these implementations follow the ECMA specification (ECMA 334 Section 10.9) which states

    For instance, if a local variable that is in scope is the only existing reference to an object, but that local variable is never referred to in any possible continuation of execution from the current execution point in the procedure, an implementation might (but is not required to) treat the object as no longer in use.”

    Hence even though on the desktop CLR it is not important to set variables to null, it is sometimes required to do so on WP7. In case t and l was set to null GC would’ve collected them. So the guidance for WP7 is

    1. In most cases setting local variables to null is not required. Especially if the function returns fairly soon
    2. If you have locals that hold onto very large data structures and that function will remain executing for a long time then set those variables to null when you are done using them (e.g. in between the last usage of a variable in a large function and calls to a bunch of web-services in the same function which will take a long time to return).
    3. Use dispose patterns where required. It’s important on devices to free up limited resources as soon as possible.
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    Windows Phone 7, my story

    Olympic Peninsula - Hurricane Ridge

    Now that Windows Phone 7 is released all the gadget/tech blogs like TechCrunch, Engadget , Gixmodo are humming with reviews. Given that it’s a Version 1 product (ignore that 7 in the phone name) the reviews are great.

    Seeing all the buzz around gets me thinking about how I got involved in the project and my experiences. As the Windows Phone 7 head said “These are the good old days”

    Not so long ago, sometime after I joined the .NET Compact Framework team (and drew this cartoon) we started hearing about Windows Mobile reset and the awesome new phone being built and how our .NET Compact framework will be it’s runtime. Then we started getting access to CEPC images (these are phone OS that works on desktop virtual machines) to start developing and debugging our code. It felt strange at the beginning to see the ugly blue tiles and the truncated or cut-off text. These CEPC didn’t have hardware acceleration and hence there was no animation. The standard PC displays clipped off most of the phone display area and made the UI look really weird. I thought it was getting the wrong font as well as the text on top seemed to be cut off. All in all I wasn’t that impressed and just didn’t get the Metro UI.

    Working on the runtime is not all that glamorous and my view of Windows Phone 7 remained pretty much confined into the debugger. I’d interact with it over command shell and see bits and bytes flying by. So this is the view at 10 feel elevation (you can ignore the source file open in the IDE Smile, I wasn’t going to give a faux pas and reveal our source code, would I?).


    As time went by and I had a chance to see the first prototype device, I suddenly “got” the Metro UI. It felt wonderful, a no pretense UI which doesn’t try to fake 3D buttons and kind of gets out of they way. The at a glance UI totally made sense (just look on the locked screen or the start window and know your email count, schedule and other bunch of things).  I started playing with the initial apps (Jelly Splat Smile) and then the realization dawned, each time someone picks up the device and launches any app, our code would start executing. Exactly the reason I joined Microsoft.

    As more and more applications started getting developed by 3rd parties the power of our developer tools really shows up. IMO with the Windows Phone Developer tools (Visual Studio 2010 based), Expression, XNA Game Studio, Emulator, Silverlight and host of other 1st and 3rd party tools, WP7 easily has the best development story out there and it’s just V1.

    Now when I see my daughter play Flowerz or I watch a Netflix movie and get a 10,000 feet view, it feels strangely wonderful and at the same time disconcerting (did you see http://abstrusegoose.com/307 ?). I strongly believe that Windows Phone 7 is one of the best Phones I have ever used and it passes the significant other test with flying colors. 



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    Windows Phone 7 App Development: When does the GC run



    If you are looking for information on the new Generational GC on Windows Phone Mango please visit http://blogs.msdn.com/b/abhinaba/archive/2011/06/14/wp7-mango-the-new-generational-gc.aspx

    Many moons ago I made a post on When does the .NET Compact Framework Garbage Collector run. Given that a lot of things have changed since then, it’s time to make another post about the same thing.

    For the developers coming to Windows Phone 7 (WP7) from the Windows desktop let me first clarify that the runtime (CLR) that is running on the WP7 is not the same as the one running on the desktop. The WP7 runtime is known as .NET Compact Framework (NETCF) and it works differently than the “desktop CLR”. For 90% of cases this is irrelevant as the WP7 developer targets the XNA or Silverlight programming model and hence what is running underneath is really not important. E.g when you drive you really do not care about the engine. This post is for the other 5% where folks do run into issues (smoke coming out of the car).

    Moreover do note that when the GC is run is really an implementation detail that is subject to change.

    Now that we have all the disclaimers behind us lets get down to the list.

    The Garbage Collector is run in the following situations

    1. After some significant allocation:
      When an application tries to allocate managed memory the allocator first checks a counter that indicates the number of bytes of managed data allocated since the last GC. If this counter crosses a threshold (which is changeable and set to 1MB currently) then GC is fired (and the counter is obviously reset).
      The basic idea is that there has been significant allocation since the last GC and hence do it again.
    2. Resource allocation failure
      If some internal native allocation fails, like loadlibrary fails or JIT buffer allocation fails due to out-of-memory condition then GC is started to free up some memory and the allocation is re-attempted (only 1 re-attempt)
    3. User code can trigger GC
      Using the managed API System.GC.Collect(), user code can force a GC
    4. Sharing server initiated
      One of the new features in the WP7 CLR is the sharing server (see my post http://blogs.msdn.com/b/abhinaba/archive/2010/04/28/we-believe-in-sharing.aspx for details). In WP7 there is a central server coordinating all the managed processes. If this sharing server is notified of low memory condition, it starts GC in all the managed processes in the system.

    The GC is NOT run in the following cases (I am explicitly calling these out because in various conferences and interactions I’ve heard folks thinking it might be)

    1. GC is not run on some timer. So if a process is not allocating any memory and there is no low-memory situation then GC will never be fired irrespective of how long the application is running
    2. The phone is never woken up by the CLR to run GC. GC is always in response to an active request OR allocation failure OR low memory notification.
    3. In the same lines there is no GC thread or background GC on WP7


    For folks migrating from NETCF 3.5 the list below gives you the changes

    1. WinForm Application going to background used to fire GC. On WP7 this is no longer true
    2. Sharing server based changes are obviously new
    3. The GC quantum cannot be changed by user
  • I know the answer (it's 42)

    Date format


    Let me start by saying that using mm-dd-yyyy is just plain wrong. No really it just doesn’t make any sense to me. Neither does it make any sense to most people world-over if you go my the date-format map up at http://en.wikipedia.org/wiki/File:Date_upd1.PNG

    If one uses dd-mm-yyyy it makes sense because it’s in decreasing order of granularity (kind of LSB first). yyyy-mm-dd makes ever more sense because

    1. It’s in decreasing order of granularity
    2. Natural ordering in many ways like telephone numbers (country-code, area-code, local-code, number) or IP address
    3. String sorting automatically sorts by that date. E.g. I can easily have folders/files named in this order and DIR lists them nicely sorted out (yea I know I can sort by date/time as well).

    d:\MyStuff\Personal\Pictures>dir 2010*
    Volume in drive D is Data
    Volume Serial Number is 3657-F386

    Directory of d:\MyStuff\Personal\Pictures

    06/17/2010  01:06 PM    <DIR>          2010_0501
    06/17/2010  01:07 PM    <DIR>          2010_0504
    06/17/2010  01:16 PM    <DIR>          2010_0508
    06/17/2010  01:20 PM    <DIR>          2010_0509
    06/17/2010  01:24 PM    <DIR>          2010_0515
    06/17/2010  01:29 PM    <DIR>          2010_0517
    06/17/2010  01:30 PM    <DIR>          2010_0523
    06/17/2010  01:33 PM    <DIR>          2010_0528
    06/17/2010  01:37 PM    <DIR>          2010_0529
    06/17/2010  01:43 PM    <DIR>          2010_0605
    06/17/2010  01:47 PM    <DIR>          2010_0606
    06/21/2010  08:40 PM    <DIR>          2010_0616
    06/28/2010  10:33 PM    <DIR>          2010_0619
                   0 File(s)              0 bytes
                  13 Dir(s)  55,925,829,632 bytes free

    But I just cannot fathom why would anyone use mm/dd/yyyy. In what way is that intuitive?

  • I know the answer (it's 42)

    Inside the Windows Phone Emulator


    Learn from the dev lead and PM of Windows Phone 7 Emulator on how it works and delivers the awesome performance.

    Some key points

    1. The emulator is essentially a x86 based Virtual Machine running full image of Windows Phone 7 OS
    2. It emulates various peripherals (e.g. audio, networking), the list hopefully will grow in the future
    3. Supports multi-touch if your host PC has a touch screen
    4. It uses the GPU on the host PC to accelerate the graphics
    5. Shameless plug: One of the reason it’s possible to emulate x86 and still have managed apps running as-is, is because the runtime (.NET Compact Framework) supports both x86 and ARM seamlessly (provides JITer for both architectures and runs the same managed code on both seamlessly)

    Get Microsoft Silverlight

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    Working in the United States

    Eucalyptus trees-  Trek in the hills

    I am sure everyone has read about the “you cannot possibly pronounce or spell” volcano in Iceland throwing up in the air and screwing up the entire flight system of this planet. While most people were reading about it from the comfort of their home I was doing the same while waiting in airports with a 5 year old tagged along. Anyways, 48 hours and a switch in the direction of flights got me to some countries I didn’t really plan to visit and over the Pacific to land in Seattle.

    Going forward I will be working out of the Microsoft Redmond offices, doing pretty much the same stuff I was doing before (working on the .NET Compact Framework runtime).

    Right now I am settling down with my family and my daughter is excited to see snow for the first time (she got lucky as there was a small snowfall on Saturday in Snoqualmie pass). The changes we need to adjust to is humongous, we left Hyderabad when it was 43° Celsius and now it’s 6° Celsius in Redmond. Oh sorry I should’ve said it was 110°F and now it’s  43°F in Redmond.

    Wish me luck and hopefully finally I will be able to attend some nerddinners.

  • I know the answer (it's 42)

    We Believe in Sharing

    Good Morning

    In Building NETCF for Windows Phone 7 series we put in couple of features to enhance startup performance and ensure that the working set remains small. One of these features added is code/data sharing.

    Native applications have inherent sharing where multiple processes can share the same executable code. However, in case of managed code running on NETCF 3.5 even when multiple applications use the same assembly, the managed code in them are JITed in context of each process separately. This results in suboptimal resource utilization because of the following

    1. Repeated JITing of the same code
    2. Memory overhead of having identical copies of the same JITed code for every process running them. The execution engine also maintains records of the various types loaded and even though two (or more) processes may be loading the same types from the same assemblies; per process copies are maintained for them.

    Together the overhead can be significant.

    In the latest version of the runtime shipping with Windows Phone 7 (.NET Compact Framework 3.7) we added a feature to share both the JITed code and these type information across multiple managed processes.


    The runtime essentially uses a client server architecture. We added a new kernel mode server which is responsible of maintaining a system wide shared heap. The server on receiving requests from the various client processes (each managed app is a client) JITs code and type information into this shared heap. The shared heap is accessed Read-only from all the client apps and Read/write from the server.

    When a process requests for the same type to be loaded or code to be JITed it just re-uses the already loaded type info or JITed code from the shared heap.
    What is shared

    1. Various Execution engine data-structures like loader type-information
    2. JITed code from a predefined list of platform assemblies (user code is not shared).

    Do note that user code is not shared and neither is all platform code. Sharing arbitrarily would actually increase cost if they ultimately didn’t get reused in a lot of applications. The list of assemblies/data shared was carefully chosen and tuned to ensure only those are shared that provided the maximum performance benefit.

    Sharing provides the following advantages

    1. Warm startup time is significantly reduced. When a new application is coming up a large
      percentage of the initial code and type-info is already found on the shared heap and hence
      there is significant perf boost. The exact number depends on the applications but it’s common
      to get around 30% gains
    2. Significant reduction in net working set as a lot of commonly used platform assembly JITed code is re-used
    3. Obviously there are other goodness like less JITing means less processing on the device

    Like user code the system is also capable of pitching the shared code when there is a low memory situation on the device.

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    What’s this .NET Compact Framework thingy?

    Bidar - On the way back to hyderabad

    If you are following the latest Windows Phone stories than you have surely heard about the .NET Compact Framework (NETCF) which is the core managed runtime used by the Windows Phone 7 programming model. This is an implementation of the .NET specification that works on devices and a disparate combination of HW and SW.


    In case you are hearing about NETCF for the first time, then hopefully this post will help you to understand it’s architecture and how it is different from the desktop .NET.

    The Architecture

    At the heart of NETCF is the execution engine. This contains the usual suspects including the JIT, GC, Loader and other service providers (e.g. Marshalling that marshals native objects to managed and vice versa, type system).

    The entire Virtual machine is coded against a platform agnostics Platform Abstraction Layer or the PAL. In order to target a platform like say Nokia S60 we implemented the PAL for that platform. Stringent policy of not taking any platform dependency outside PAL and ensuring in PAL we only use features that are commonly available on most modern embedded OS allows NETCF to be highly portable. Currently the PAL supports a variety of OS and processor architecture. The ones in Red are those that are used for Silverlight, the others are available for the legacy .NETCF 3.5.

    The other system dependent part is the JITter which compiles the MSIL into the platform dependent instructions. For every supported processor architecture there’s a separate implementation of JIT.

    This entire runtime is driven by a host. E.g. for Silverlight on S60 it’s the Silverlight host running as a plugin inside the Nokia browser, on Windows Phone it’s the Windows Phone task host. These hosts uses the runtime services to run managed code. The host interacts with the runtime over the hosting interfaces.

    Managed code can either be the framework managed code like BCL and other Silverlight/XNA framework managed code or the user code that is downloaded from the web/application-store. Even though the framework managed code can interact with the underlying system including the execution-engine and the OS (via Platform-Invoke) the user managed code is carefully sandboxed. If you see the arrows moving out of the user managed code it is evident that user managed code can call only into the framework managed code (which in turn can call into the system post security verification). User code is not allowed to access any native resources (including P/Invoke).

    The host knows about the UI and it’s rendering and uses reverse Invoke to call into the managed code. E.g. if a user clicks on a XAML button the Silverlight host using the XAML object tree and rendering logic (hit-testing) figures out which object got clicked on and it uses reverse-pinvoke to call into the corresponding managed objects (which provides the event handler). That managed code is then verified, security checked, jitted and run by NETCF.


    NETCF is highly portable. As far as I know it’s one of the very few (or is it the only one :)) runtime shipping out of Microsoft that supports Big-Endian processor architecture (Xbox360 uses Big-Endian processor). It is designed for resource constrained devices and is battery friendly. For many time-space trade-offs it tilts towards conserving space (e.g. Code-pitching which I’ll cover later) and at the same time works well on Xbox360 running high-end games. The list of processor/OS I have given above is just illustrative and it actually works or there are POC (proof-of-concept) of it working on really esoteric SW+HW combinations.

    Some CF Facts

    1. Design Goals
      1. Keep the runtime highly portable, that is the main NETCF USP
      2. Designed for resource constrained devices
      3. Battery friendly (use less power)
    2. Nothing comes for free. The above design results in some unique NETCF features (more about that later) and some limitations as a consequence.
    3. Some of the well known platforms powered by NETCF runtime is Windows Mobile 6.5 and below, Windows Phone 7, XNA (on Xbox 360), Zune, Media Room (pdf), Silverlight on Nokia S60.
    4. Currently shipping versions are 3.7 on Windows Phone and 3.5 elsewhere.
    5. Windows Phone runs on both ARM (the real phone devices) and x86 when running on the emulator (which is a x86 VM). NETCF becomes a natural choice because it runs on both these processors.
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    Comparing Windows Phone with .NET Compact Framework 3.5

    Bidar - Fort

    In the comments of my previous post Windows Phone 7 Series Programming Model and elsewhere (e.g. twitter, WP7 forum) there seems to be a lot of confusion around how NETCF 3.5 compares against the new WP7 programming model powered by NETCF 3.7. People are asking why some API got removed from 3.5, or is 3.7 a subset of NETCF 3.5 as they are not seeing some familiar 3.5 APIs.

    First I’d urge you to go visit the Windows Phone 7 Series Programming Model to see what it offers.

    Essentially NETCF 3.5 can be broken down to

    1. NETCF 3.5 runtime (the Execution Engine)
    2. NETCF 3.5 BCL
    3. NETCF 3.5 UI programming model (WinForm based)

    Now each of this has been updated (in order) as follows

    1. NETCF 3.7 runtime (hugely updated Execution Engine)
    2. NETCF 3.7 BCL (essentially offering the Silverlight 3 BCL Apis with a small delta)
    3. The UI model has been replaced and offers two options
      1. Silverlight 3 UI + Windows Phone device specific features (e.g. accelerometer , location service)
      2. XNA features with Windows Phone device specific features (e.g. accelerometer , location service)

    So the runtime is hugely updated (and hopefully you’d feel the improvements, especially in performance).

    For #2 and #3 the level of difference is same in magnitude as you compare WinForm with Silverlight on desktop. They are simply two different programming models.

    In case you hit a 3.5 API  that’s missing then it’s either because it’s (a) WinForm based API that got totally replaced, or (b) a BCL API that the Silverlight profile doesn’t support. The workaround is to search for how to do the same thing in Silverlight (e.g. use XDocument instead of XmlDocument). In some cases you’d get into situations where there is no direct alternative. E.g. there is no P/Invoke and if your code say P/Invoked to get data from a bar-code scanner you cannot do so now.

    Also keep in mind that the bits available right now is just early preview bits and subject to a lot of change. The whole purpose of having CTPs is to hear our customers and ensure we use the remaining time before release in fixing issues that helps our customers the most. Hopefully some of the gaps will get closed before the final release.

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    Silverlight on Nokia S60 platform

    Bidar - Fort

    Today at MIX 2010 we announced Silverlight beta for Nokia S60 phones. Go download the beta from http://silverlight.net/getstarted/devices/symbian/

    Currently the supported platform is S60 5th Edition phones and in particular the 5800 XpressMusic, N97 and N97 mini. It works in-browser and only in the Nokia default web-kit based browser.

    Silverlight on S60 uses .NET Compact Framework (NETCF) underneath it. I work in the dev team for the Execution Engine of NETCF and I was involved at the very beginning with getting NETCF to work on the S60 platform.

    NETCF is extremely portable (more about that in later posts) and hence we didn’t have a lot of trouble getting it onto S60. We abstract away the platform by coding against a generic platform abstraction layer (PAL), but even then we had some challenges. Getting .NET platform on a non-Windows OS is challenging because so much of our code relies on Windows like functionality (semantics) which might not be available directly on other platforms.

    As I was digging through emails I found the following screenshot that I had sent out to the team when I just got NETCF to work on the S60 Emulator…


    As you can see the first code to run was a console application and it was not Hello World :). We have come a long way since then as evident from the touch based casual game running on the N97 shown below


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    Windows Phone 7 Series Programming Model


    Bidar - Barid Shahi tombs

    Just sometime back I posted on the MIX 2010 announcements. One of the major aspects of the announcement was

    “The application model supported on Windows Phone 7 series will be managed only and will leverage Silverlight, XNA and the .NET Framework”

    That’s a mouthful and includes 3 framework names in once sentence :). This was already disclosed and has resulted in some flutter over the web and twitter. Let me try to explain how these 3 interplays in the application model with the following diagram


    Managed only

    First of all the application model allows users to write only managed code (to repeat native code is not allowed). That means they do not have direct access to any native APIs and cannot use platform-invoke to call into native user or system code. So all resources including phone capabilities have to be accessed using the various managed APIs provided.

    Two Flavors of applications (XNA and Silverlight)

    There are 2 variants or flavors of applications users can write, XNA Games and Silverlight applications. Obviously the former is for writing games and the later is for your typical phone applications (nothing stops you from writing a Silverlight animation based game though). So you cannot mix-match SL and XNA UI in the same application.

    However, do note that the traditional NETCF development using WinForm based UI is not supported.

    Common Services available to both

    That said, beyond the UI rendering and controls there is the common services which both SL and XNA applications can use. This includes all the phone capabilities like microphone, location, accelerometer, sound, media, networking, etc... Some of these features come from SL and others from XNA but land up in the common pool usable by either types of applications.

    Core Runtime is .NET Compact Framework 3.7

    The core runtime for both SL and XNA applications is .NET Compact Framework (henceforth called NETCF). This is the team I work for.  .NETCF is a highly portable and compact (as in smaller size and footprint) implementation of the .NET specification. It is designed to run on resource constrained devices and on disparate HW and SW configurations.I will have a post later on the detailed architecture or .NETCF.

    Over the last two years a lot of work has gone into .NETCF to scale it in terms of features, performance and stress to meet the requirements of Windows Phone and other newer platforms on which it is being targeted. We also added a lot of features which I hope you will enjoy. Some of the features is just to reach parity with the desktop CLR and others are device specific and not available on the desktop.

    Over this blog in the course of the coming months I’ll try to share with you what all we did to reach here.

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    MIX 2010 Announcements

    Bidar Trip - Mohamad Gawan Madrasa

    Today is a very big day for me and my team. The stuff we have been working on is finally went live on stage MIX 2010.

    Windows Phone 7 is easily the most dramatic re-entry/reset Microsoft has undertaken in any field it’s in. We announced the phone in MWC and the reception it got was phenomenal. However, in the new connected devices world, the application platform+market story is as or more important than the device itself. Today at MIX we just disclosed details of that.

    1. The application model supported on Windows Phone 7 series will be managed only and will leverage Silverlight, XNA and the .NET Compact Framework. So basically you can reuse your C#/.NET and Silverlight skills to build amazing experience on the phone. I will get into details of this in the coming posts
    2. Microsoft just announced free Windows Phone Developer Tools (preview bits available for download head over to http://developer.windowsphone.com/ )
      1. This builds on the amazing development experience brought in by the Visual Studio 2010 shell.
      2. You can either get a standalone Visual Studio 2010 Express for Windows Phone Or an addin for your previously installed VS 2010
      3. Windows Phone 7 series emulator (yes you do not even need a device to develop for Windows Phone)
    3. A version of Expression Blend is also demonstrated for the Windows Phone (a free version will be available for download in the coming months)
    4. A new Windows Phone Marketplace is being put into place
      1. Developers can earn 70% revenue from the applications they sell of the marketplace
      2. The registration to the market place is not free but it’ll be free for the DreamSpark program for students

    Our team was involved with building the IDE, the emulator and the core .NET runtime that powers the applications. So watch out and in the coming posts I’ll deep dive into these areas.

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    Back to Basics: Memory leaks in managed systems

    Kolkata Trip 2009

    Someone contacted me over my blog about his managed application where the working set goes on increasing and ultimately leads to out of memory. In the email at one point he states that he is using .NET and hence there should surely be no leaks. I have also talked with other folks in the past where they think likewise.

    However, this is not really true. To get to the bottom of this first we need to understand what the the GC does. Do read up http://blogs.msdn.com/abhinaba/archive/2009/01/20/back-to-basics-why-use-garbage-collection.aspx.

    In summary GC keeps track of object usage and collects/removes those that are no longer referenced/used by any other objects. It ensures that it doesn’t leave dangling pointers. You can find how it does this at http://blogs.msdn.com/abhinaba/archive/2009/01/25/back-to-basic-series-on-dynamic-memory-management.aspx

    However, there is some catch to the statement above. The GC can only remove objects that are not in use. Unfortunately it’s easy to get into a situation where your code can result in objects never being completely de-referenced.

    Example 1: Event Handling (discussed in more detail here).

    Consider the following code

    EventSink sink = new EventSink();
    EventSource src = new EventSource();
    src.SomeEvent += sink.EventHandler;
    sink = null;
    // Force collection

    In this example at the point where we are forcing a GC there is no reference to sink (explicitly via sink = null ), however, even then sink will not be collected. The reason is that sink is being used as an event handler and hence src is holding an reference to sink (so that it can callback into sink.EventHandler once the src.SomeEvent is fired) and stopping it from getting collected

    Example 2: Mutating objects in collection (discussed here)

    There can be even more involved cases. Around 2 years back I saw an issue where objects were being placed inside a Dictionary and later retrieved, used and discarded. Now retrieval was done using the object key. The flow was something like

    1. Create Object and put it in a Dictionary
    2. Later get object using object key
    3. Call some functions on the object
    4. Again get the object by key and remove it

    Now the object was not immutable and in using the object in step 3 some fields of that object got modified and the same field was used for calculating the objects hash code (used in overloaded GetHashCode). This meant the Remove call in step 4 didn’t find the object and it remained inside the dictionary. Can you guess why changing a field of an object that is used in GetHashCode fails it from being retrieved from the dictionary? Check out http://blogs.msdn.com/abhinaba/archive/2007/10/18/mutable-objects-and-hashcode.aspx to know why this happens.

    There are many more examples where this can happen.

    So we can conclude that memory leaks is common in managed memory as well but it typically happens a bit differently where some references are not cleared as they should’ve been and the GC finds these objects referenced by others and does not collect them.

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    .NETCF: The mini Y2K

    Kolkata Trip 2009

    I am sure most people haven’t yet forgotten the Y2K problem. This year our team faced a mini Y2K, but don’t worry we anticipated it and all is well.

    If you head over to NETCF Wikipedia page you’d notice the NETCF versions look as follows


    A sample version number is


    This represents .NETCF version 3.5 build on the 283rd day of 2007. I guess by now you can guess the problem. We use a single digit to represent the year. By that nomenclature, the version of the build churned out today would be 3.5.0001.0 which is lower than the one generated the year before and would fail to install.

    These numbers are automatically generated by scripts on the server that churns out daily builds. The numbering system was invented a long time ago in early 2000 and no one bothered to fix it. We anticipated that it’s going to fail as we move into the new decade and have updated it to now have 2 digits for the year (and yes we know it will break again in the future, but hopefully that’s too far out to care right now).

    Happy new Year.

  • I know the answer (it's 42)

    Some things I have learnt about SW development

    Kolkata Trip 2009

    Working in the developer division is very exciting because I can relate so well with the customers. However, that is also an issue. You relate so well that you tend to evolve some strong opinions that can cloud your view. While working in the Visual Studio Team System team and now in the .NET Compact Framework team I have learnt some lessons. I thought I’d share some of them

    I am not *the* customer (or rather the only customer)
    Even though I represent the customer in different avatars (sometimes as a developer, sometimes as an office worker, sometimes just as a geek) I am not THE only customer that the product targets. When your product is going to be used by 100,000 developers/testers the average or even the predominant usage is going to be very different from what you think it will be. Sitting though an usability study is a very humbling experience. Like I believed that everyone should just be using incremental search.

    Consistency is important
    Geeks and bloggers tend to over-tout coolness. While cool user experience (UX) seems awesome, it is frequently overdone and what seems cool on casual usage tends to tire soon. Consistency on the other hand lets your users get on-board faster and lets them spend time doing stuff they care about and not learning things that should work automatically.

    Consistency doesn’t mean that every application needs to look exactly like notepad. Expression Blend is a great example which looks refreshingly cool (appeals to the designers) and at the same time provides an experience that is consistent to other windows apps.

    Learn to let go
    ”If there’s not something you can actively do on a project, if it’s something you can only influence and observe, then you have to learn to provide your feedback, and then let go and allow other people to fail… People don’t learn if they never make any mistakes” ~ Raymond Chen on Microspotting

    Corporate software development is very different from Indie development. Large software development projects have a bunch of people/teams involved. It is not necessary that the collective opinion matches yours. At some point you need to learn to let go and do what is required. As an example I can debate on what a Debug Assert dialog should look like or do. However, there are other folks to design and think about the UX, as a developer I need to give inputs and once the call has been made it’s my job to provide the best engineering solution that implements that UX**.

    ** Do note the debug assert dialog is a fictitious example, I never worked on the IDE side.

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    Indic Language Input

    Diwali 2009

    If you have tried inputting Indian languages in Windows you know it’s a major pain. That is particularly sad because Windows comes with very good support of Indian languages. I had almost given up using my native language Bengali on a computer due to this. Even when I was creating the About Page for this blog and wanted to have a version in Bengali, I had to cut it short a lot because typing it out was so painful.

    There are web-based tools like the Google Transliteration tool that works well for entering text into web-pages where they are integrated (e.g. Orkut). However, I wanted a solution that pans the desktop, so that I can use it for say writing a post using Windows Live Writer.

    Enter the Microsoft Indic Language Input tool. Head over to the link and install the desktop version. You can install the various languages individually (currently Bengali, Hindi, Kannada, Malayalam, Tamil and Telugu is supported). I personally installed the Bengali and Hindi versions.

    Since I am on Windows 7 which comes pre-installed with Complex language support I needn’t do anything special. However, on older OS like XP you need to do some extra steps which are available through the Getting Started link on that page.

    Once you are setup you can keep the Windows Language Bar floating on the desktop. The tool extends the language bar to allow you to enter Indic languages using an English keyboard via transliteration.


    Go to the application where you want to enter Indic language and then switch to Bengali (or any of the other 6 supported Indic language) using this language bar. Start typing বেঙ্গলি using English keyboard and the tool will transliterates. The moment you’d hit a word terminator like space it inserts the Bengali word.


    I tried some difficult words like কিংকর্তববিমূঢ় and it worked amazingly well


    I had a very good experience with the tool. The only issue I faced was that the tool was extremely slow with some WPF apps like Seesmic twitter client. However, I got to know from the dev team that they are aware of the issue (it’s for some specific WPF apps and not WPF in general). I hope they fix it before they RTM (the tool is in Beta).

    Tip: You can hit alt+shift to cycle the various languages in the toolbar without having to use your mouse (which is handy if you typing using a mix of languages).

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    NETCF: Count your bytes correctly


    I got a stress related issue reported in which the code tried allocating a 5MB array and do some processing on it but that failed with OOM (Out of Memory). It also stated that there was way more than 5 MB available on the device and surely it’s some bug in the Execution Engine.

    Here’s the code.

        byte[] result;
        long GlobalFileSize = 5242660;  //5MB
        result = new byte[GlobalFileSize];
        string payload = Encoding.UTF8.GetString(result, 0, result.Length);
        System.Console.WriteLine("len " + payload.Length);
    catch (Exception e)
        System.Console.WriteLine("Exception " + e); 

    The problem is that the user didn’t count his bytes well. The array is 5MB and it actually gets allocated correctly. The problem is with the memory complexity of the UTF8.GetString which allocates further memory based on it’s input. In this particular case the allocation pattern goes something like

      5MB  -- Byte Array allocation (as expected and works)
      5MB  -- Used by GetString call
     10MB  -- Used by GetString call
      5MB  -- Used by GetString call
     10MB  -- Used by GetString call

    So GetString needed a whooping 30MB and the total allocation is around 35MB which was really not available.

    Morale of the story: Count your bytes well, preferably through a tool like Remote Performance Monitor

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    Silverlight: Where are my colors

    Barsha Mangal 

    The Silverlight System.Windows.Media.Colors class is a trimmer counterpart of the WPF Colors class. E.g. Colors.AliceBlue is available in WPF but not present in Silverlight. However, these standard colors are indeed available in Silverlight XAML.

    In effect in Silverlight XAML you can use

    <Border Background="AliceBlue" BorderBrush="Coral" BorderThickness="2" CornerRadius="10" >

    However, if you try that in code it fails to compile

    foo.Background = new SolidColorBrush(Colors.Coral);

    This means if you ever need to use standard colors in Silverlight code you have to use RGB values, which for Coral would be something like

    foo.Background = new SolidColorBrush(Color.FromArgb(255,255,127,80));

    This is kind of painful. Moreover, you need to frequently be able to convert between HTML color, RGB and XAML standard color names when you are developing an Silverlight application. To make the job easier I hacked up a small Silverlight 2 app at http://www.bonggeek.com/Ag/Colors/. You can do the following with this

    1. Change colors with sliders, RGB, HTML, XAML standard color names to see what the color really looks like
    2. All the format is kept in sync, this means if you change the sliders to get to the color Salmon then the RGB value and HTML will be updated and the drop down will switch to show the selected colors name
    3. You can easily create variants of standard color. E.g. select Salmon using the drop down and then push the sliders to get to a slightly lighter/darker shade of the color


    Enjoy and extend as you please. Sources are available here.

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    Global variables are bad

    Hyderabad Zoological Park

    <This post is about C++ (C# folks are saved from this pain)>

    One of our devs taking care of NETCF on Nokia S60 reported that after the latest code reached their branch things are working very slow. It was observed that Garbage Collector is getting kicked in way more than it should. Investigation showed something interesting.

    I added a global var gcConfig which had a fairly complex constructor and that among other things sets the various member variables like the GC trigger threshold to default value (1mb). All of these works fine on Windows variants.

    However, TCPL states “It is generally best to minimize the use of global variables and in particular to limit the use of global variables requiring complicated initialization.”. This is especially true for dlls. We tend to ignore good advice sometimes :)

    For Symbian OS (S60) on device complex ctors of global objects are not run (without any warning). The members are all set to 0 (default member initialization). So in the gcConfig GC-trigger was being set to 0 instead of 1mb. The allocation byte count is compared against this value to figure out when it’s time to start a GC. Since it was 0 the collection condition is being met for every allocation and hence for every allocation request GC was being fired!!!

    Actually considering that even after that the app was actually running shows that we have pretty good perf ;)

    A good alternative of using global vars is as follows

    MyClass& useMC()
        static MyClass mc; // static ensures objects are not created on each call
        return mc;
    MyClass& mc = useMC();

    Do note that this has some multi-threading issue. See http://blogs.msdn.com/oldnewthing/archive/2004/03/08/85901.aspx.

  • I know the answer (it's 42)

    .NET Compact Framework BCL < .NET BCL

    Hyderabad Zoological Park

    Over twitter some folks are regularly discussing about the fact that there are some chunks of desktop .NET Base class library (BCL) that are missing on the .NET Compact Framework (.NETCF). So I thought I’d post the rationale behind things that are missing and what criteria is used to figure out what makes it in.

    First of all, .NET and .NETCF use completely different runtimes. So the BCL code doesn’t work as is. They need to be ported over. Something being available on the desktop reduces the effort of our BCL team but still significant cost is involved in making it work over NETCF. This means that its not as if everything is available on .NETCF BCL and we cut things out (elimination process), but the other way round where we start from 0 and we need to figure out whether we can take something in. In that process we use some of the following rationale.

    1. ROI: Does the user scenario that it enables on a mobile device justify the cost
      System.CodeDom.Compiler. Yea right you expected to compile on the phone didn’t you :)
    2. Easy workaround available: If there is an acceptable workaround for a given API then it drops in priority. A trivial example could be that we ship some method overloads but not the other. E.g. Instead of shipping all overloads of Enum.Parse we drop Enum.Parse(Type, String) and keep only Enum.Parse(Type, String, Bool).
      This applies at the level of namespace or Types as well.
    3. Lower in priority list: It needs work to get it done and it’s lower in priority than other things that is keeping the engineering team busy.
      If there are a lot of request for these features and not good/performant workarounds available then it will go up the priority list and make it to future version of NETCF
    4. Too large to fit: Simply too large to fit into our memory limitations
      E.g. Reflection.Emit which leads to other things missing like Dynamic Language Runtime, Linq-to-SQL
    5. No native support: It uses some underlying OS feature which is either not present on devices or is not relevant to it
      WPF, Parallel computing support

    With every release developers ask for new features and we also negotiate to increase NETCF footprint budget so that we can include some (but not all) from those requests. To choose what makes it in we use some of the criteria mentioned above.

    Given the system constraints under which NETCF works a vast majority of the desktop APIs will continue to be missing from NETCF. Hopefully this gives you some context behind why those are missing. If you approach NETCF simply from trying to port a desktop application then you would face some frustration on the missing surface area.

    BTW: Do post your comments on this blog or on twitter (use the #netcf hashtag).

    <Update: I made some updates to this based on feedback />

  • I know the answer (it's 42)

    NETCF: GC and thread blocking

    Hyderabad Zoological Park

    One of our customers asked us a bunch of questions on the NETCF garbage collector that qualifies as FAQ and hence I thought I’d put them up here.

    Question: What is the priority of the GC thread
    Answer: Unlike some variants of the desktop GC and other virtual machines (e.g. JScript) we do not have any background or timer based GC. The CLR fires GC on the same thread that tried allocation and either the allocation failed or during pre-allocation checks the CLR feels that time to run GC has come. So the priority of the GC thread is same as that of the thread that resulted in GC.

    Question: Can the GC freeze managed threads that are of higher priority than the GC thread?
    Answer: Yes GC can freeze managed threads which has higher priority than itself. Before actually running GC the CLR tries to go into a “safe point”. Each thread has a suspend event associated with it and this event is checked by each thread regularly. Before starting GC the CLR enumerates all managed threads and in each of them sets this event. In the next point when the thread checks and finds this event set, it blocks waiting for the event to get reset (which happens when GC is complete). This mechanism is agnostic of the relative priority of the various threads.

    Question: Does it freeze all threads or only Managed threads?
    Answer: The NETCF GC belongs to the category “stop-the-world GC”. It needs to freeze threads so that when it is iterating and compacting managed heap nothing on it gets modified. This is unlike some background/incremental GC supported by other virtual machines.

    GC freezes only managed threads and not other native threads (e.g. COM or host-threads). However, there are two exclusions even on the managed threads

    1. It doesn’t freeze the managed thread that started GC because the GC will be run on that thread (see answer to first question)
    2. Managed threads that are currently executing in native p/invoke code is not frozen either. However, the moment they try to return to managed execution they get frozen. (I actually missed this subtle point in my response and Brian caught it :))

    Hope this answers some of your questions. Feel free to send me any .NET Compact Framework CLR questions. I will either answer them myself or get someone else to do it for you :)

  • I know the answer (it's 42)

    I am the Empire


    NH5 to Vizag

    5 years back exactly on this very day I walked into Cyber Towers office of Microsoft India for the first time. If someone asked me at that time how long I plan to work for Microsoft, my answer would’ve been couple of years max. I was still a bit suspicious of the evil empire and it took some time for me to realize that “I am the empire”. The 5 years has been a mind blowing journey.

    Even though in our industry working for any company for a 5 year stretch is a huge thing, it doesn’t seem so in Microsoft. Our team has 4 people over 20 years and at least 8 people over 10 years.

    Some random thoughts on the last 5 years

    1. Made my family relocate 3 cities before settling down in Hyderabad (my wife’s threat that the next relocation would be without her helped).
    2. Bought an apartment
    3. I have a daughter now who was born around 3 months after I joined MS.
    4. Started working in a shared office with Ankur and then worked in various cubicles. Finally I have an office.
    5. 3 job designations. SDE to SDEII to Senior SDE. I am fiercely protecting the SDE suffix.
    6. It’s fantastic to walk into a book store and see books on your work and see screenshots of UI you’ve designed or description of algorithms you’ve come up with.
    7. 327 blog posts on blogs.msdn.com
    8. I still do not use Visual Studio to edit code
    9. Finally gave up on Linux even at home. Bye bye Ubuntu, welcome Windows 7
    10. I have 3 Xboxes in my office and none at home
    11. I use Nokia phones
    12. Made fantastic friends at work and sadly few of them are left with Microsoft India (either moved to Redmond or have left MS). Hello Amit, Srivatsn, Ankur :)
    13. Always wanted to attend a BillG project review but he quit
    14. Got into some email wars
    15. I am no longer the fire-head I used to be. I actually think before I speak.
    16. Went top down from n-tier architectures (TFS), desktop applications (VSTT) and now embedded (NETCF)
    17. I prefer Starbucks coffee now instead of Darjeeling tea
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