We Believe in Sharing

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.

Silverlight on Nokia S60 platform

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

Silverlight: Where are my colors

 

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.