MSDN Magazine - August 2008 - (Page 20)

tion is obfuscated and access is exist on the Mac and thus had to be implemented entirely in limited to the application that owns the store. the PAL (see Figure 2). Quotas for isolated storA lot of the Silverlight PAL age are defined by application benefits from lessons learned groups, which are based on the when we developed the Shared domain name of the Silverlight Source Common Language application. For example, two Infrastructure (SSCLI), also Microsoft applications, located Figure 2 Platform Adaptation Layer known as Rotor. The SSCLI ran in directories under microsoft.com, would share an application on a number of UNIX-style platforms as well as Windows. The group, meaning that both applications share the same quota. By base OS functionality varies widely on UNIX-style platforms. The default, an application group is given 1MB of storage. SSCLI PAL had to work on both microkernels (such as the Mach However, if an application needs additional storage space it can kernel in Mac OS X) and monolithic kernels and had to cope with request a larger quota by prompting the user with a dialog box that different OS services such as threading, exception handling, and would specify, for example, that microsoft.com wants to increase its networking stacks. Because Silverlight only targets Windows and quota to 8MB. Users can enable or disable isolated storage as well Intel Mac machines we were able to write Mac-specific implemenas delete current uses of it in the Silverlight configuration dialog tations for many of the functions in the PAL, which helps with the (it is called Application Storage in the dialog). Application groups size and performance of the PAL. also can have shared stores, which enables related applications to The PAL only supports the subset of Win32 necessary to enable share data among them. Silverlight to run. There is no need to support the registry, GDI+, or COM. We didn’t implement Windows on top of the OS X, nor did we implement enough of Windows to support the full capabilities of the desktop CLR. Limiting the PAL to support only Silverlight allows it to be small and fast. Hiding the differences between operating systems is a tricky problem when you consider just how different OS X is from Windows. Much of OS X is written in Objective C and exposes an exception handling system which is incompatible with C++. The CLR creates I/O threads, which are separate from worker threads. These While isolated storage has been around for some time, its uses are based on I/O Completion Ports that were introduced in Winhave never been as compelling as they are with Silverlight. A con- dows NT® 3.5 and don’t exist on OS X. Even something as simple figurable, secure file system for interactive Web applications al- as locating a file is different on Mac because of the backslash dilows development of traditional office applications, such as word rectory delimiter in Windows. processors, or applications that maintain large quantities of data, Throughout the design and development of the CoreCLR we’ve such as stock-tracking systems. focused on providing an environment that allows developers to reuse existing skills and tools to develop rich content for a small, Working Cross Platform secure runtime. Most of our decisions were driven by the reduced Silverlight will run on non-Windows platforms. We have a part- scenarios of rich Internet applications, but some designs also bennership with Novell to support Linux through the Mono project’s efited from looking at some of the work we have done in the past. Moonlight runtime. Microsoft also is working on a version of Silver- Some of the decisions we made with CoreCLR will eventually light for the industry-leading Symbian OS and Windows Mobile®. make their way back into the desktop. For example, you can look Moonlight runs on Mono, and the mobile version of Silverlight will forward to the next version of the desktop CLR running side-byrun on the .NET Compact Framework (which has a much lower side in process with other versions of the CLR. Also, most of the memory footprint than CoreCLR). But the Mac OS X version of changes made for the improved Security Transparency model will Silverlight runs on the exact same CoreCLR as on Windows. appear in our next CLR. We accomplished this with the help of a Platform Adaptation We carefully considered what made sense for Web-based scenarLayer (PAL). The PAL is an API written to work against different ios and what didn’t need to be in the runtime. We hope we’ve made platforms. It provides abstractions for error handling, file handling, the right choices and trust that you’ll tell us how we can continue networking services, threading semantics, and so forth. Functions to improve. Have fun coding against Silverlight 2, and keep your in the PAL share the names of Win32® APIs but differ in imple- eye on this space for deeper dives into CoreCLR in the future.  mentation. Some of the APIs just pass through the PAL function’s parameters to an OS X function, whereas others need to use cus- Andrew PArdoe is a program manager for CLR at Microsoft. He works on all tom logic to match up OS X functionality with Windows API sig- aspects of the execution engine for both Silverlight and the desktop runtime. He natures. Some Windows functionality used by CoreCLR doesn’t can be reached at Andrew.Pardoe@microsoft.com. The PAL supports only the subset of win32 necessary to enable Silverlight to run. 20 msdn magazine CLR Inside out http://microsoft.com

Table of Contents Feed for the Digital Edition of MSDN Magazine - August 2008

MSDN Magazine - August 2008 Toolbox CLR Inside Out Basic Instincts Cutting Edge Patterns in Practice Data 2.0 - Expose And Consume Data In A Web Services World Biztalk EDI - Build A Robust EDI Solution With BizTalk Server Silverlight - Create Animations With XAML And Expression Blend Write On! - Create Web Apps You Can Draw On With Silverlight 2 Wicked Code - Craft Custom Controls For Silverlight 2 Team System Foundations Windows With C++ Concurrent Affairs Going Places { End Bracket }

MSDN Magazine - August 2008

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