MSDN Magazine - January 2009 - (Page 76)

The CoreCLR has a very simple code access security (CAS) model—simpler than in the desktop CLR because Silverlight only needs to enforce security policies at the application level. This is because, as a platform-independent Web client, it can’t rely on any particular enterprise or machine policies being in effect, and it should not allow a user to change existing policies. There are a few exceptions, such as OpenFileDialog and IsolatedStorage (storage quota change), where Silverlight needs the user’s explicit consent for breaking the sandbox default rule set. OpenFileDialog is used for accessing the file system, while IsolatedStorage is used to access the namesakeisolated storage and increase the storage quota. For desktop applications, each executable loads exactly one copy of the CLR, and the OS process will only contain one application. Each application has a system domain, a shared domain, a default domain, and a multitude of explicitly created AppDomains (see “JIT and Run: Drill into .NET Framework Internals to See How the CLR Creates Runtime Objects” at msdn.microsoft.com/magazine/cc163791 for more on this subject). A similar domain model is found in the CoreCLR. In the case of Silverlight, several applications, possibly from different domains, will be running in the same OS process. In Internet Explorer 8.0, each tab runs in its own isolated process; thus all the Silverlight applications hosted inside the same tab will be running in the context of the same CoreCLR instance, as illustrated in Figure 2. As each application can be from a different domain of origin, for security reasons, each application will be loaded into its own AppDomain. There will be as many instances of CoreCLR as there are tabs currently hosting Silverlight applications. Similar to the desktop CLR, each AppDomain will get its own pool of static variables. Each domain-specific pool will be initialized during the AppDomain bootstrapping process. Silverlight applications can’t create their own custom application domains; that ability is reserved for internal use. For a more detailed discussion of the CoreCLR, refer to the following CLR Inside Out columns from the CLR team: “Program Silverlight with CoreCLR” (msdn.microsoft.com/magazine/cc721609) and “Security in Silverlight 2” (msdn.microsoft.com/magazine/cc765416). Silverlight Runtime Silverlight is designed for a broad range of applications that require varying degrees of framework and library support. A simple application may, for example, just play audio files of a few bytes to help with the pronunciation of words on a dictionary Web site or display a banner ad. On the other hand, enterprise class LOB applications require security, privacy of data, state management, integration with other applications and services, and instrumentation support, to name a few. At the same time, Silverlight needs to have a smaller runtime so that deployment over the Internet will not be a problem on slower connections. Not Implemented in the Demo Cross-Domain Policy Server (TCP Server) os s lic -Dom yM a sg in s d an op gs n P Ms ree Sc ssion Se AdvCallClient (Silverlight) Po Call Manager (TCP Server) Telephony Events (For example, incoming call) Third-Party Call Control Simulator (Silverlight) Cr Call WCF Services Business Services (AdvBusinessServices) (WCF HTTP Server) Business Entity CRUD Msgs Silv erli ght and P Oth er W ackage s eb C onte nt Se c Ev urit en y t M and sg s SL Application Web Site (Advcallclientweb) (ASP.NET Web Site) Business Entity CRUD Msgs ty Enti ess gs n Busi D Ms CRU ty Enti urity sgs Sec D M CRU Customers, Orders, and Reps Users, Security Policies Utility Services (advutilityservices) (WCF HTTP Server) Instrumentation Events Event Logs Figure 1 Silverlight Call Center Logical Architecture 76 msdn magazine Silverlight Enterprise Apps http://msdn.microsoft.com/magazine/cc721609 http://msdn.microsoft.com/magazine/cc765416 http://msdn.microsoft.com/magazine/cc163791

Table of Contents Feed for the Digital Edition of MSDN Magazine - January 2009

Toolbox CLR Inside Out Basic Instincts Cutting Edge Test Run First Look� Geneva Framework Silverlight Windows Mobile Service Station Security Briefs Extreme ASP.NET Foundations .NET Matters { End Bracket }

MSDN Magazine - January 2009

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